KDMPower MIPC MI-X8775CD [PCB WF-C rev:E]

[Th3_uN1Qu3]

Re: KDMPower MIPC MI-X8775CD [PCB WF-C rev:E]

Who was the OEM on the Spire? I remember I have a Sun Pro AT-2005B based one

Sun Pro and it had the AT2005B also.

[Dan81]

Re: KDMPower MIPC MI-X8775CD [PCB WF-C rev:E]

Who was the OEM on the Spire? I remember I have a Sun Pro AT-2005B based one (which someone recased into a RPC shell, of all things, lol - I think it was a 380W unit, and *should* do its rated power I guess) and two YX-GP labeled ones that claim 420W - they're the shiny golden SP-ATX-420WTN-PFC models.

[Th3_uN1Qu3]

Re: KDMPower MIPC MI-X8775CD [PCB WF-C rev:E]

Heck, does a half-bridge design over 500 Watts even exist as far as ATX PSUs go? If yes, I don’t want to know how much one of those weights or what kind of BJTs it has on the primary.

Yes. There's a 450W Spire with Passive PFC. It does do rated power. It's HEAVY.

It uses TO-3P D209Ls on the primary, the PI filters are complete, input caps either a pair of 680uF 250v or 1000uF 250v, output toroid large. Transformer is a tad bigger than the one in yours iirc, and I made it into a 600W +/-30V and +/-12v supply for my amplifier. Just the PCB was left of it for that purpose though.

[goodpsusearch]

Re: KDMPower MIPC MI-X8775CD: load-tested and still running… for now (part 2)

(I guess goodpsusearch was right in suggesting to leave the extra rectifier on the 12V rail… though I still think the PSU would do better with one bigger rectifier on the 12V rail vs. two smaller ones.)

I agree! It will also highly depend on the Vf (forward voltage drop).

[sam_sam_sam]

Re: KDMPower MIPC MI-X8775CD [PCB WF-C rev:E]

Thanks for the information

[momaka]

Re: KDMPower MIPC MI-X8775CD: load-tested and still running… for now (part 2)

Do you need something to limit the current with this setup ( I do have a Variac unit I have a 5 amp and a 15 amp ) both of have been modified with a volt meter and current meter

If the PSU decides to blow up, you might want to implement something to limit the current, indeed. Otherwise if you don't care, then no.

This might answer the first question but how do you “calculations” are you talking about the limited function of the power supply because of current limiting device that is in place

I'll probably need to make an Excel spreadsheet for that, as it might be easier to understand.

In general, however, again you just have to know that for an "ideal" maximum power draw, the line AC voltage should be approximately split in half between the series heating element and the PSU... thus each consuming up to 1/4 of the rated power of the heating element. Of course, as I noted above, most PSU's simply won't work at half the AC line voltage, and typically the minimum is 90-100 V for 120V-rated devices and 190-200V for 220/230/240V -rated devices. Therefore, the load you put on the PSU should be much smaller so that the input voltage won't drop as much. IME, taking 1/2 to 1/3 of the 1/4-power rating of the heating element (i.e. 1/8 to 1/9 total) is probably *around* the maximum load you can put on the PSU. So with a 500 Watt heating element for example, the 1/4 rating is 500 / 4 = 125 Watts. Taking 1/2 of that is ~60-ish Watts... or ~42 Watts with 1/3. So with a 40-60 Watt load on the PSU output, most likely the voltage on the PSU input would be just high enough for the PSU to stay working. And then, to induce a low input AC line, just continue increasing the load (power draw) on the PSU output (i.e. connect more fans, light bulbs, HDDs, or whatever else.) The more you load the PSU output, the more power (and thus current) the PSU will draw on the input / AC side, which means more voltage dropped across the series heating element. As you continue increasing the load on the PSU, the line input should eventually reach an level where the PSU shuts off and stop working (or not, like the PSU in this thread.)

Would you recommend making a “ test jig ” that basically has a outlet that the heat element is in series with the main power coming and outlet to the device that is being tested

You can, if you're going to use it often.
On that note, I actually did make one many years ago... but for some reason just never got to using it before (probably because I never added a proper input plug on it) and completely forgot about it until now. So thanks for reminding me. Maybe I will put it to use. Here's what I have:
https://www.badcaps.net/forum/showpo...&postcount=183

Would you need a cooling fan or water to cooling the heating element

No, if the heating element is made to run at full power without active cooling.

In the case of my toaster oven... well, it's a toaster oven, and those heating elements inside are meant to get red-hot under max load (which you will never see in a series configuration in normal operation - unless your PSU short-circuits and you don't notice and leave the setup running like that for a while.)

In the case with the 500W dishwasher heating element... I'm not sure if it's made to run at max power without being in water, so I can't say. I think it is, as I think that's how dishwashers "dry" the dishes on the dry cycle. But because that heating element would run hot left air-coupled, I would need to put it on something that won't burn. A brick or two would do the job. But I chose the pot of water, as that's cleaner than bringing dirty bricks from outside (which I don't even have ATM.) Also, I originally started using that heater in that pot of water back in late December when we had some really cold temperatures and the air got really dry from the house heating. Thus closing my work area door (and air vents in the room), then running the heating element at half power (via. single diode half-wave rectification) kept the water in the pot right around 50-60C mark - perfect where it's releasing a lot of moisture in the air but not boiling. In short, it was my ghetto air humidifier.

But no, you don't need to cool your heating elements if they are designed to take full power without need for active cooling. Most cooking oven elements are of this type.

Of all of the heating elements that you were talking about earlier which would you use and why

Any toaster ovens and toasters come first, as the heating elements in those can run in "free air" without active cooling. Then curled stovetop/burner heating elements, as those *can* usually take full power while being in "free air"... though they are really designed to have a "load" (i.e. in contact with a pan or pot) on top of them. Other than these considerations and the power rating, there really is no difference which one you choose/use. I used the ones shown here because that's just what I have on hand. (Well, I have a couple more parts boxes in the garage that I haven't looked through what's in there... though I do recall I have a few more different heating elements around. )

[sam_sam_sam]

Re: KDMPower MIPC MI-X8775CD: load-tested and still running… for now (part 2)

Well, if you have a Variac, that would probably be easier than my setup above: you just power ON the PSU with a load and then slowly lower the input AC voltage with the Variac until the PSU shuts off (or in the case with this cheapo PSU, probably blow up, if current on the input is not limited - which in my case it was, due to the series heating element.)

Do you need something to limit the current with this setup ( I do have a Variac unit I have a 5 amp and a 15 amp ) both of have been modified with a volt meter and current meter

Since I don't have a Variac, the series heating element I used was just an "improvised" substitute... and it also helped limit current on the AC input, which is always helpful when testing something you've fixed and don't know how it will do. So essentially, the series heating element help me get "2 birds with 1 stone". The downside is you have to do a few calculations prior to rigging the setup to get a rough idea of what it can and can't

This might answer the first question but how do you “calculations” are you talking about the limited function of the power supply because of current limiting device that is in place

The 500W one, if I'm not mistaken, was the heating element you see on the bottom of dishwashers. I'm not 100% sure if that's where it came from, though, because I got it from a dumpster many years ago.

The 700/1400 Watt heating element is actually a mini toaster oven that I have in my kitchen. It's just an older type with mechanical switches (i.e. no "smart" electronics that I have to bypass to get it to turn on in the above experiments.) It has 2x 350 Watt heating elements on the top in parallel (i.e. 700W total) for the "broil" function. The bottom also has 2x 350 Watt heating elements in parallel (another 700 Watts), but these come ON with the top heating elements only when the "Bake" function is used (thus, getting all four 350 Watt heating elements in parallel for a total of 1400 Watts.) So depending on whether I have the knob on "bake" or "broil", I can switch between 1400 and 700 Watts on-the-fly.

Would you recommend making a “ test jig ” that basically has a outlet that the heat element is in series with the main power coming and outlet to the device that is being tested

That being said, you can use just about any appliance that has a heating element in it - toasters, sandwich presses, rice cookers, coffee makers... and many others. Just make sure the appliance uses an actual Nichrome -based heating element and not some kind of an induction coil, as I'm not sure how that will work out. Also, better to make sure the appliance is the "dumb" type - i.e. no "smart" electronics, LCD displays, or "soft" buttons, as those probably won't let you turn ON the device.

Better yet, just grab a bunch of oldschool "curled" stovetop/burner heating elements. They can be found for about $10-15 usually (though some years back, Amazon was selling a few at $4 a pop with free S&H.). Most are typically rated 1-3 kW @ 208/230/240V.

Just remember that when running an resistive Nichrome heating element at half of its rated voltage, its output power will drop to 1/4 of its rating. So for example, a 1.2 kW (1200 Watt) heating element rated for 240V AC will output only 300 Watts at 120V AC (i.e. 1200 / 4 = 300W ).

Would you need a cooling fan or water to cooling the heating element

Basically I want to make something that I could use with ease and not have to set something up each time I want to troubleshoot some switching power supply issue or issues

Of all of the heating elements that you were talking about earlier which would you use and why

[momaka]

Re: KDMPower MIPC MI-X8775CD: load-tested and still running… for now (part 2)

But I have a couple of question for you, you point out the fact that at low input voltage that it should have locked out and not restart but is this with a load or with out ( first of all )

It doesn't actually matter. The 5VSB may try to start, and that's OK, because it's designed to run all the time. But the main PS (3.3V, 5V, and 12V rails) should not try to keep running when the AC line voltage drops too far (typically 95-100V.) Thus, once the line drops too far, the main PS should shut down and stay off - and by this, I mean the PSU should at least stay off until the PS-ON signal is cycled again, if not until AC power cycled.

I also tested an Enermax ELT400AWT on that same setup (haven't posted the results in its thread yet, though) and that one would not try to run below 90-ish V AC, if I remember correctly. Once the AC input dropped below ~90V, the main PS shut off (5VSB kept running, though). I could get the PSU to try to start again by cycling the PS-ON signal, but the PSU would do the same thing (try to power on, see that it can't really run on that low of an AC line, and shut off and stay off), which is fine. The KDMPower PSU, on the other hand, just tries to keep running as long as the PS-ON signal was held low, and that's NOT OK.

Second what is the correct way to test the low voltage lock out

Well, if you have a Variac, that would probably be easier than my setup above: you just power ON the PSU with a load and then slowly lower the input AC voltage with the Variac until the PSU shuts off (or in the case with this cheapo PSU, probably blow up, if current on the input is not limited - which in my case it was, due to the series heating element.)

Since I don't have a Variac, the series heating element I used was just an "improvised" substitute... and it also helped limit current on the AC input, which is always helpful when testing something you've fixed and don't know how it will do. So essentially, the series heating element help me get "2 birds with 1 stone". The downside is you have to do a few calculations prior to rigging the setup to get a rough idea of what it can and can't handle.

What if it does not work correctly what should you do to make it safer to use if your ATX switching power supply has this issue

That, I haven't figured out yet.

But generally, if the PSU detects a fault (be it a short-circuit on the output, an abnormally-low AC input, or over-voltage on one of the outputs, and etc.), it should shut off and stay off until the PS-ON signal is released (allowed to go high again) at the very least. On most PSUs that use STF designs with current-mode PWM controllers (like UC384x or CM6800/CM6802), the PSU will usually even latch down in the OFF state until the AC power is cycled.

Where did you get a heater element that is only 500 to 700 watts

The 500W one, if I'm not mistaken, was the heating element you see on the bottom of dishwashers. I'm not 100% sure if that's where it came from, though, because I got it from a dumpster many years ago.

The 700/1400 Watt heating element is actually a mini toaster oven that I have in my kitchen. It's just an older type with mechanical switches (i.e. no "smart" electronics that I have to bypass to get it to turn on in the above experiments.) It has 2x 350 Watt heating elements on the top in parallel (i.e. 700W total) for the "broil" function. The bottom also has 2x 350 Watt heating elements in parallel (another 700 Watts), but these come ON with the top heating elements only when the "Bake" function is used (thus, getting all four 350 Watt heating elements in parallel for a total of 1400 Watts.) So depending on whether I have the knob on "bake" or "broil", I can switch between 1400 and 700 Watts on-the-fly.

That being said, you can use just about any appliance that has a heating element in it - toasters, sandwich presses, rice cookers, coffee makers... and many others. Just make sure the appliance uses an actual Nichrome -based heating element and not some kind of an induction coil, as I'm not sure how that will work out. Also, better to make sure the appliance is the "dumb" type - i.e. no "smart" electronics, LCD displays, or "soft" buttons, as those probably won't let you turn ON the device.

Better yet, just grab a bunch of oldschool "curled" stovetop/burner heating elements. They can be found for about $10-15 usually (though some years back, Amazon was selling a few at $4 a pop with free S&H.). Most are typically rated 1-3 kW @ 208/230/240V.

Just remember that when running an resistive Nichrome heating element at half of its rated voltage, its output power will drop to 1/4 of its rating. So for example, a 1.2 kW (1200 Watt) heating element rated for 240V AC will output only 300 Watts at 120V AC (i.e. 1200 / 4 = 300W ).

have you ever cut and stripped one of the centech probe leads??
i doubt it - or you wouldnt have put 111v through one!

Actually, I have - not on my own meters, though (I have 3 of these.) Just seen a few in the past with the wire breaking off from the probe handle (very common problem with cheap multimeters.) The wire inside is indeed really laughably thin. The insulation, however, isn't that bad - probably comparable to that of standard-rated 300V wire... though that's not so good, considering many of these cheap meters have dials indicating they can measure up to 1000V DC or AC, which is downright DANGEROUS given their construction. That said, my 3rd Cen-Tech meter is a newer, "revised" version - dial sticker was changed to indicate that the meter can measure only up to 250V (AC or DC) and the unfused current jack downgraded to 5 Amps. But most importantly, the wires on the test probes that came with this 3rd meter are considerably thicker than on the older two versions I have. I've tested the old wire and the new one. The old one will get very warm with just 2-3 Amps of continuous current. And at 5 Amps it's borderline not melting (soft / "flaccid" would be a good way to describe it - which is funny, considering the wire one these meters is normally quite stiff when cold. ) IIRC, I think it was someone on here who measured how much current these cheap wires can handle, and the result was (again, IIRC) that at 6-7 Amps, those old wires will melt. The wire on my 3rd (newer) meter, also gets warm at 5 Amps, but not nearly as much as the old one. HF also added a bunch of safety-related notes on the label and in the manual regarding max. voltage and current, among other things. My guess is they probably got bit by complains / small claims / lawsuits against them before, so the newer revision of the meter covers their asses just a tad better and comes with slightly safer leads... though they will still fall apart at the handle unless glued - which I did to all 3 of my meters as soon as I got them, and their probes are still 100% intact and in good condition after many years of use.

In any case, I'm still well aware of the shortcomings of these cheap meters. I actually posted a thread here on the first one I got a while back. I don't use them anywhere that involves unlimited/unchecked current and high voltage. In the test setups I've showed above, both voltage and current were within fairly safe margins of what these meters can handle, so it's not a big issue. And most importantly, I set everything up for "hands-free" operation, so I'm not touching the probes or changing the settings on anything that's live. That's actually the reason why I got so many of these cheap meters - so I can put one on each spot I want to measure and not have to diddle with moving probes around.

[sam_sam_sam]

Re: KDMPower MIPC MI-X8775CD: load-tested and still running… for now (part 2)

After the above tests, it was clearly time to step it up. Unfortunately, my current load test setup with all the jumper leads was not longer up to the task. ******************************
***********************************************************
I knew this PSU would be another “fun” repair project, but I didn’t know it’s going to kick off so many ideas for so many other projects / tests.

I was impressed with the way you went about torture testing your ATX switching power supply

But I have a couple of question for you, you point out the fact that at low input voltage that it should have locked out and not restart but is this with a load or with out ( first of all )

Second what is the correct way to test the low voltage lock out

What is the correct way to test this function

What if it does not work correctly what should you do to make it safer to use if your ATX switching power supply has this issue

Where did you get a heater element that is only 500 to 700 watts

[stj]

Re: KDMPower MIPC MI-X8775CD [PCB WF-C rev:E]

changing the subject slightly,
have you ever cut and stripped one of the centech probe leads??
i doubt it - or you wouldnt have put 111v through one!

i cut one to put clips on the end - after i saw the "conductor" i threw the cables in the bin!!

[momaka]

KDMPower MIPC MI-X8775CD: load-tested and still running… for now (part 2)

After the above tests, it was clearly time to step it up. Unfortunately, my current load test setup with all the jumper leads was not longer up to the task. Clearly, I needed to make something that would drop less voltage. A few days later, I cobbled something together with a 20-pin ATX connector from an old motherboard, a 4-pin 12V CPU connector, and a 6-pin 12V PCI-E power connector. Soldering good thick wires to these (16 AWG) and adding proper nut connectors at the end allowed me to draw the full 6 Amps of current from each heating element in my load bank.

As such, I tried the following load setup next: 2x 6 Amps (12 Amps total) from the 12V rail, 2.5 Amps from the 5V rail, 1.74 Amps from the 3.3V rail, and of course a 1.3 Watt load on the 5VSB + a 1.2 Watt load from a 12V mm fan running @ 5V to cool the load bank. I didn't take pictures for this one, but the total load (given the nearly same output voltages from the PSU) yielded about 172.6 Watts of draw from the DC side. Of course, this wasn't without one very important change: I swapped the 500-Watt heating element for a 1400-Watt heating element (a mini toaster oven with heating elements configurable for either 700W or 1400W, depending if broil or bake setting was chosen.) This change allowed me to draw the 172.6 Watts from the output with the AC input line staying at a steady 94.5V. Doing all of the calculations again, I came up with 219 Watts for the primary side and efficiency moving up a notch at 78.8%. Again, this is not bad at all. With the efficiency still increasing, this means the PSU is far from its limit.

Before moving to the next test, however, I ran the above config for about 5 minutes straight and then unplugged and opened the PSU to check temperature inside it. To my surprise, the primary heatsink wasn't hot at all like I expected it to be with the low AC line voltage, and neither was the output toroid. Both were just slightly warm. Granted I only ran the test for about 5 minutes and my room temperature around this time of the year is a steady 17.5-18°C (63-64°F.) So looks like the PSU still had headroom on those. The secondary heatsink, on the other hand, was quite warm… though still nowhere near burning hot. (I guess goodpsusearch was right in suggesting to leave the extra rectifier on the 12V rail… though I still think the PSU would do better with one bigger rectifier on the 12V rail vs. two smaller ones.) Of course if the PSU is ran all day with that load and at higher ambient temperatures, I wouldn't be surprised to see the secondary heatsink reach 65-80°C. The hottest component, by far, had to be… guess what? - The NTC inrush thermistor. I couldn't even keep my finger on it. I can see now why they add relays in parallel on high-power PSUs – over 2-3 Amps, and the power dissipated by the NTC becomes a lot greater than what the secondary coil of a relay would use (not to mention high power NTCs could get expensive.) Apart from the NTC, the small CM choke I added was also very hot. Not sure if this is due to the AC line passing through it or because of its proximity to the NTC thermistor. My guess for now, is the latter.

In terms of voltage regulation, the PSU did fairly OK now. 12V rail was still around 12.2V. Meanwhile, the 5V rail actually improved a little by dropping down to 5.17V. And the 3.3V rail was a bit high at 3.41V, but still in spec and IMO a good result, considering it was the least loaded of the main rails at 1.74 Amps. With that said, I think the designer(s) of this PSU probably “cheated” a little and intentionally wound the 12V rail to output slightly higher voltage all the time so that the PSU would do OK in any 12V-heavy PC. I didn't do a 5V-heavy cross-load to see how that will go, but I probably eventually will. My suspicion, of course, is that this PSU won't do well at all with that...

Last test consisted of me trying to pull 3x 6 Amps (18A total) on the 12V rail with still the same 2.5 Amps on the 5V rail, 1.3 Watts on the 5VSB, and 1.2 Watt fan (3.3V rail left unloaded this time.) All in all, that would have been about 230 Watts from the DC side. But considering the AC input was already at ~95V with the 172-Watt DC load above, I expected the AC line should drop below what the PSU can function at normally. And sure enough, that's exactly what happened… except the MI-X8775CD did not shut down and tried to continue to run… which is NOT a good thing at all! Because the input AC line was clearly too low (varying between 50 and 80V AC ), the PSU appeared to be pulsing on and off at very high frequency… to the point where the output on the 12V rail was reading around 8-10V and the 5V rail was reading 2.5 to 3V. Ugh! Imagine what this could do to your PC hardware! There was also a nasty loud 120 Hz hum noise emitted by the PSU. It looks like the primary was self-limiting after all, but the PSU just wouldn't latch and stay off. As long as I had the PS-ON signal jumped to ground, it would try to keep running.

Suffice to say I did not run the above test for more than a few seconds. After all, I didn't want to burn out the primary BJTs again, as I don't have any more replacements currently on hand. I'm pretty sure that if I didn't have the series heating element and if the PSU was left to run at such low AC line, it would likely have blown up pretty quickly. I opened it up briefly after this test, and just for the few seconds of abuse, the primary heatsink was starting to feel a tad bit warm, while everything else was still cool.

I'm pretty sure I could pull 18 Amps from the 12V rail if I connected the PSU directly to the wall. But given the abuse I just have to the PSU, I didn't want to risk it. Instead, I ran some numbers and calculated that I could pull additional 3 Amps on the 12V rail (from the test where I had it at 12A) if I could somehow boost the AC line after the series heating element. This is where a UPS transformer came to the rescue. Wired with its primary and secondary windings in series and primary powered from the AC line, this brought a nice 12V AC boost on the PSU input … which at no load was close to 134V AC (meaning each 200V cap inside the PSU was sitting at close to 190V )

So I configured the PSU for about 15.5 Amps on the 12V rail, with the other rails same as before (2.5A on 5V, 1.3 Watts on 5VSB, and 1.2 Watt fan on 5V)… thus, about 203 Watts DC load. Then I jumped PS-ON to ground. The PSU buzzed again with that 120 Hz hum, but only for a short moment, after which the output voltages came up normally and PSU started running OK. At this DC load, the AC input going to the PSU read 84.3V with the boosted AC voltage. Due to the UPS transformer boosting the voltage (and not knowing exactly how much, though it really should have been 12V AC), the calculations for the power draw of the PSU on the primary and its efficiency may not be entirely accurate. But what I came up with is about 60% efficiency at this load… which may be right, given the very low AC input at 84.3V that barely allowed the PSU to run this test. But hey! It survived that one as well. 5V rail was still the same at ~5.15V, while the 12V dipped only a slight bit to 12.08V.

Overall, I'm glad to see the PSU manage up to 200 Watts of DC load, with most of that on the 12V rail too… not to mention the silly-low AC input line. I'm just not so excited about the fact that it doesn't shut down with a low AC input. Ideally, it should refuse to power on at anything under 95-100V AC. Kind of makes me wonder if such circuit could be implemented and whether I should attempt that with this PSU. Also makes me wonder how other half-bridge PSU will fare with such a test. Another point to mention is the 5V rail regulation was not that great either. Looks like the manufacturer clearly built this PSU with a 12V-based PC in mind. So it's quite possible this PSU will do terrible with an old Athlon or Pentium 3 PC. And lastly, I would also like to determine, if possible, where the OPP protection is set on this unit and also if other protections (such as short-circuit and over-voltage) work too.

I knew this PSU would be another “fun” repair project, but I didn't know it's going to kick off so many ideas for so many other projects / tests.

[momaka]

KDMPower MIPC MI-X8775CD: load-tested and still running… for now (part 1)

As promised, I did some load testing on this PSU. The results were better than I expected in some ways, and just as bad as I thought they would be in others. But before I go off digging in numbers, let’s talk about the test “setup” first, accompanied by a visual (picture.)


Oh, look at that perrrty blue fan! The MI-X8775CD does look good, I give it that. But that’s not the focus of the picture. Rather, it’s that red multimeter showing the AC line input voltage going to the PSU and the stainless steel pot behind. No, I won’t be dropping this PSU in water while running, if that’s what you were thinking. The whole plan of the “setup” is to have a heating element in series with the PSU input line – same thing, actually, as having an incandescent light bulb to limit the current. However, the reason for going with the heating element is to allow more power through… and the water to keep it cool. This way, I can load-test the PSU (to an extent) and not worry if something goes wrong with it, as the series device (heating element) would limit current (and power.) And since the series device causes the AC line going to the PSU to drop slightly (or more than slightly, depending on load), I can see at what input AC voltage (if any) the PSU would shut down. After all, ATX PSUs are rated for a certain input voltage range. Going below this range (low AC voltage, simulating a long brown-out condition) should NOT damage the PSU if it’s designed properly, and the PSU should shut down / refuse to start. But did it? We shall find out later.

In the case above, I used a 500 Watt heating element inline with the AC going to the PSU. It might seem like a very high limit, but remember that this is only if the PSU is completely short-circuited on the AC side, allowing full voltage to be present across the heating element (and hence, full power.) Otherwise, if the PSU is to operate, then the highest power it can draw with that series element is when the AC line is equally split in half between it and the heating element, yielding about 125W from the series device and 125 Watts from the PSU. But AC line split in half equally means the PSU would have to be operating at 60V input. Clearly, that’s a bit too low, as most SMPSes are typically specified to work at no less than 95-100 V AC input, regardless of design. So if the PSU is to see at least 90-100V on its input, then it shouldn’t be loaded too much.

Again, going back to the picture/case above, I had a 12V, 20 Watt halogen bulb on the 12V rail of the PSU and an incandescent bulb drawing 1.5 Watts from the 5V rail. With this DC load (approximately 21-22 Watts total), you can see how the series heating element was dropping voltage on the AC line, leaving the PSU to work with only 111V AC. The AC at the wall was in fact 120V, though:
https://www.badcaps.net/forum/attach...1&d=1614667911

So where does the stainless steel pot come into play? Well, it was full of water… but again, not for dropping the PSU in it while it’s powered on. Rather, I had the heating element placed in it (it is a submergible type, BTW), so that it could stay at a steady temperature and yield a more steady resistance… which I measured at around 29.5 to 30 Ohms. Knowing the resistance of the heating element along with the AC line voltages with and without load allows me to estimate the current (and power) the PSU is drawing on the primary (this is something a Kill-a-Watt could do too, BTW.) To get that, we take the no load voltage (120V) and subtract the load voltage from it (111V), giving us 9V across the 500 Watt heating element. This means the current going through it must be 9V / 30 Ohms = 0.3 Amps… which is also the AC current the PSU is drawing on the primary, since it’s in series. At 111V AC input, the PSU is drawing approximately 111V x 0.3 Amps = 33.3 Watts with the 21-22 Watt DC load on the output. Efficiency-wise, that comes out to 22 / 33.3 = 66%... which is downright terrible. Of course, keep in mind many PSUs have poor efficiency at such low loads. The regulation, on the other hand, should have been passable at this low load… and it wasn’t, to say the least:


Red multimeter shows the 12V rail and the gray RS one shows the 5V rail. While the 12V rail was still in spec (albeit a little high), the 5V rail was low and outside of ATX spec at 4.5V. Looks like the PSU needs a bigger load on the 12V rail.

Of course, the above load test was just more for me to see if the PSU works without blowing up (as I haven’t really properly tested it ever since it was fixed) and to see if the numbers added up… which they did, as I confirmed with my Kill-a-Watt meter also hooked to the same setup. So up next I added a bigger load on the 12V rail and repeated the same test.


Red and gray multimeters show the 12V and 5V rails are now in spec (though the 5V is just barely so, but that’s another item for discussion.) The black one shows the current draw on the 12V rail: about 5.66 Amps into a resistive load bank. Actually, that resistive load bank measures about 1.8 Ohms, so the current should have been a little over 6 Amps. But due to all of the resistance from the jumper leads I was using, there was a lot of voltage drop on the jumper leads’ wires and thus the current was lower. Nonetheless, this is still more than 3x bigger load than the first test at around 71 Watts total… which is getting somewhat close to the 125 Watt limit at half AC voltage. Speaking of which, let’s see what the AC we got now.


Ooof! 89.9V That’s a very low AC input voltage. When I saw this, I was surprised the PSU even ran with normal voltage regulation on the output (well, as normal as it gets for this PSU. ) I even shut it off after a few seconds to check if anything was getting hot inside, but it wasn’t. The PSU was actually running OK at this low voltage… which is not really a good thing. At this low of a line voltage, it should be shutting down. However, I think a lot of half-bridge designs (especially cheap ones) have this problem, and will continue to try running even at abnormally low AC input until something cooks.

In any case, I proceeded with running the same calculations as I did above. Now we can see the AC current was about 1.02 Amps, making the AC-side power consumption about 91.73 Watts. So with approximately 71 Watts of load on the output, the total efficiency was now 77.5%... which is not bad at all for a cheapo half-bridge PSU like this, and especially given the low AC input line at not even 90V. As you can see, increasing the load to more normal levels does change efficiency quite a bit.

[momaka]

KDMPower MIPC MI-X8775CD: assembled with input filter (v1)

OK, so I was cleaning up some of my other open/unfinished projects the other day and decided to put this KDMPower PSU back together too. Surely I could solder the input wires and slap it shut again. But it bothered me to leave it with no input EMI/RFI filter. Plus, I bought a few cheap common-mode EMI/RFI chokes a while back from eBay and wanted to test them. These are really tiny (14 mm OD, 8 mm ID, 5 mm thickness) with rather thin wires (20 AWG?) I already checked that they can handle up to 3 Amps of AC current without melting (they did get warm, though not as bad as when I tested them at 5 Amps of AC current. ) So I figured if there is a crappy PSU worthy of these cheap chokes, it would be this KDM PSU. And to go with that, I also dug out a 0.22 uF X2-class cap that I pulled from an ancient CRT TV board over a decade ago.

As soon as I got to installing these parts, I ran into a problem/dilemma. Remember that tiny fuse hidden under the NTC thermistor?
https://www.badcaps.net/forum/attach...8&d=1605593160
Well, the manufacturer of this PSU was so cheap that instead of installing jumpers to bypass the missing EMI/RFI choke, this is where they placed the fuse - saving time and components that cost nearly nothing.

This meant that if I wanted to install a choke, I'd have to move the fuse.
- But where to?! Sure there is a spot on the PCB for it, but it's for a vertical fuse… and I didn't want to solder ugly extension leads to the existing fuse to make it fit there. Not only that, but I would also have had to heat-shrink the fuse to make sure it couldn't arc-over if it blew. And overall, it seemed too close to the NTC… which is where things get even more interesting, as the NTC is not connected on the same trace/line as the fuse, and rather on the opposite one. So it would be preferable if they are spaced a little further apart.

Anyways, after a lot of pondering and thinking about something so trivial on such a POS PSU, this is the crude and basic primary EMI/RFI filter I whipped together:

In the end, I decided not to mess with reusing the original “mighty” fuse … which by the way, is only rated for 3.15 Amps (though it is a slow-blow type), and yet it still managed to defeat the original no-name cheapo “13009” BJTs, which blew open first. Sure makes me wonder how crappy the rest of the parts in this PSU must be then. Anyways, that 3.15 Amp fuse got replaced with an even more “super-powered” 4 Amp, 250V round fuse. I went with that choice because the round fuse lead pitch fit perfectly the holes on the PCB, and because I have a bag of these (salvaged from a trash can at my last job - why anyone would throw away good fuses is a mystery to me. )

Yeah, replacing a smaller fuse with a bigger one is never really a great idea. Then again, if I was to actually follow the PCB marks on this PSU, I'd have to have installed either an F8A or F6.3A 250V fuse. Ha! Screw that! But you know what is more worrisome than this now? Look at the Live and Neutral labels. See anything out of the ordinary? If not, here's a visual hint:
https://www.badcaps.net/forum/attach...1&d=1614405269

How about now?
.
.
.
.
If you thought “swapped Live and Neutral”, then you got it right.
On the above picture, you can see the hole that is labeled for the Live wire takes on the top trace, goes through the NTC thermistor, and then to the rest of the PSU (bridge rectifier.) Meanwhile, the lower hole is labeled for the Neutral wire, which connects to one of the holes for the fuse. So they designed the PCB for the fuse to go on the Neutral! I mean, this is not a super-huge deal (especially in Europe, where with the directional ambiguity of the Schuko plug, Live and Neutral can be swapped around.) But in North America it sort of is, especially since the power switch is a single-pole type and on the Live only.

Of course, I noticed this PCB design “mishap” only after installing the fuse and finishing the input filter. Again, it's not a terribly huge deal, but it sure made me mad, wanting to smash the PSU. For a moment, I thought I might have to do some trace cutting and other rewiring to get everything done properly. But then I figured an easier solution:

Probably not the best picture to show it, but you can see my easy solution: take a permanent parker and just change the Live and Neutral labels, then connect wires accordingly.
There! Now the fuse will be on the Live wire.
After dong this, though, I came to another realization: the voltage selector switch would now be wired to the Live as well. Again, this is not a big deal and the PSU would work fine like that too (all it does is it bypasses two diodes in the bridge rectifier and connects the Neutral directly to the “mid point” of the two primary electrolytic caps.) However, I've noticed in other PSUs it's just standard design that the voltage selector switch is always connected to the Neutral (probably due to the switch's proximity to the case?) So to fix this new “issue” too now, I disconnected the voltage selector switch wire from point “SWB” on the PCB and instead drilled a new hole in front of the bridge rectifier on the opposite (now Neutral) trace.

While still on the discussion of PCB design/layout, let's look back to this again:
https://www.badcaps.net/forum/attach...1&d=1614405269
So you see how the distance of the optocoupler and transformer pins between the primary and secondary side is at least 5-6 mm, as are the primary and secondary traces where the input wires are soldered to? This is to prevent any arc-over from primary to secondary. However, look at the trace after the fuse and the secondary-side trace next to it - they are much closer together. This is yet another design flaw of the PCB! There's a good chance this unit may not pass a high-pot test… and probably why we don't see any safety agency marks on the label.

There's more PCB goofiness, though…
Remember how I mentioned there's a spot on the PCB for a connector for a PPFC coil?
https://www.badcaps.net/forum/attach...8&d=1605593160
Well, look at the bottom (solder) side of the PSU again in post #1.
…
This connector is placed on the positive rectified line after the bridge rectifier. That means if a PPFC coil is installed, it would be fed rectified DC current instead of AC… which doesn't make much sense, IMO. Moreover, in North America or any place with 110-120 V AC line, this location for the PPFC coil makes it quite *useless* - at least for ½ of the AC wave cycle. Why? Because with the voltage doubler circuit active (i.e. 110-120 V AC operation), only when the “upper” input cap is charging is when the PPFC coil will work. For the “lower” input cap, current will not go through the PPFC coil as it charges. Therefore, installing a PPFC coil in a PSU like this and using it in a country with 110-120 V AC mains will make the PPFC coil very ineffective. So in essence, the manufacturer of this PSU clearly designed the PPFC coil only with 220-240V countries in mind… and if I had to guess, that means mostly for Europe, since that's one of the few places where PFC is required for electronics above a certain power level. Meanwhile, I also checked a HiPro and a Bestec PSU with PPFC coils, and those had them connected to the AC line right before the bridge rectifier, as I expected.

Anyways, I know that is a lot of writing and discussion for such a cheap POS PSU. But the more I dig in there, the more flaws and shortcomings I find. Sure the PSU can still work at the end of the day, despite these. But it goes to show that such cheap PSUs are not just about using less and inferior/smaller components. Rather, it seems that they also lack a good deal in terms of design.

Up next, I will be doing some “unconventional” load tests. So feel free to stay tuned for those. Oh, and if some of you may be wondering why I didn't put any Y2-caps in the input filter - don't worry! I will go back in there and revise/improve it, if this PSU manages to survive the tests. As I stated in the beginning of this post, I just wanted to put the PSU back together to clear my projects area a little. On that note, as I was putting it together, I finally had enough of that silly label peeling itself off. So I tore it off and did this:

Yes, label now resides inside the PSU. I was going to throw it away, but figured why not slap it on the inside as an extra insulation between the primary components and the case. The way I have it in there will also not allow it to peel itself off anymore, as it's held by the fan on the top and the insulation sheet in the middle and bottom. Plus, it can stay to remind me of how over-rated this PSU really was. As such, I will probably need to whip out a new label… but that will come at the end, after testing and all. Heck, I still haven't changed the original Hangcon / Kangcon caps, and those will certainly have to go if I want to put this PSU in a PC.

So there's more to come.

[sam_sam_sam]

Re: KDMPower MIPC MI-X8775CD [PCB WF-C rev:E]

Still cooking up a plan for a PSU load tester (or rather, I just need to get down to building it - I have most of the parts already...

Please post your progress on this project I would be very interested to see want you come up with

Thanks

[momaka]

Re: KDMPower MIPC MI-X8775CD [PCB WF-C rev:E]

You're welcome guys.
I still haven't made much progress past fixing it. Still cooking up a plan for a PSU load tester (or rather, I just need to get down to building it - I have most of the parts already... it's just too cold in the garage this time of the year now, so that's what's kind of keeping me back a little.) Once that is complete, though, I think this might be the first PSU to go through it... well, we will see.

Also, the 20 Amp rectifier I stole from its 12V rail - that one has worked really nicely in an older Delta 300 Watt PSU, which originally only had a 16 Amp fast recovery rectifier. Now the 12V rail is about 0.1 to 0.2V higher under load on the Delta PSU. Before, it used to drop down to 11.8x Volts under moderate load. Now it's 11.95V or more. So a nice little improvement there. I don't think this KDMPower PSU will miss it, TBH... because again, I doubt I will be able to pull so much current from the 12V rail before the primary blows up.

And on that note, I might also steal the PCI-E power cables from it for a better Enermax PSU I am currently fixing up.

[goodpsusearch]

Re: KDMPower MIPC MI-X8775CD [PCB WF-C rev:E]

Thank you

[sam_sam_sam]

Re: KDMPower MIPC MI-X8775CD [PCB WF-C rev:E]

Thanks for sharing this repair

[momaka]

KDMPower MIPC MI-X8775CD [PCB WF-C rev:E] - repaired! (part 2)

But then I had an idea. What if I use another working H-bridge PSU and take the driver pulses from it to try and drive the C945's in the KDM PSU? Seemed like a legit idea, so I tried it. The guinea pig PSU was this gutless Cyberlink PSU - another ultra-low-end CWT unit that I didn't mind loosing to an experiment, if something went south. That didn't happen, though. The way I wired it: the c945 Base-drive signals were taken from the Cyberlink PSU and dumped via jumper wires onto a breadboard, where I had a pair of C945 transistors with their Emitters and Collectors wired to the KDM PSU.
Why do it like that?
- Because there's no way to tell if the SDC2921 drive pins (which should be open-collector outputs) might try to “fight” or short the Base drives signals from the KDM PSU to ground. So this way, the Base of the C945 BJTs on the breadboard becomes only driven by the Cyberlink PSU and not connected to the KDM PSU board.

Once everything was wired, I connected PS_ON to ground only on the Cyberlink PSU. This should have made voltages also appear on the output of the KDM PSU, even if there was a fault on its output somewhere. But it didn't happen! The KDM PSU just made a slight “tick” noise, and that was it, with the output rails again going up no more than a few mV.

This didn't make sense! The KDM PSU should have done something more. But it didn't! After thinking for a while, at least this re-affirmed me that perhaps the SDC2921 may not have been the cause (which is good, because I found only one listing on eBay for this IC, and it was for a lot of 5 for $6 total - not expensive, but I dislike buying ICs that I would never end up using.)

Back to the drawing board and schematics… I suspected the driver transformer next. Thus, I looked into my transformer/inductor parts boxes and found the driver traffo from that gutless JNC/Meico PSU I mentioned above. What a trooper - it keeps on providing parts I need! This is why I DON'T throw away even the most gutless of PSUs.

I extracted the driver transformer from the KDM PSU and connected the one from the JNC in there temporarily with some wires on the back side (and taking good care to make sure the windings were all hooked in the correct order - which I did by looking at the original PCB of the JNC PSU… which now houses a fuse and some high-power diodes I use for other experiments nothing can R.I.P. here, lol! ).

While at it, I also put the original driver transformer of the KDM PSU next to the JNC one, just to show the differences. Note how much smaller the driver transformer of the KDM PSU is with its 16 mm core (vs. 19 mm on the JNC one.) And I thought that JNC PSU was “gutless”! What's more insulting is that the JNC PSU was only rated for 235 Watts, yet still has a bigger driver transformer, BJT resistors, and diodes, than the KDM PSU. This re-affirms my notion that the KDM PSU is really just another sub-300 Watt H-bridge unit. As such, no point in keeping the 2nd parallel MBR20100CT rectifier on the 12V rail, because this PSU just can't provide that kind of power anyways. So I removed it to upgrade other PSUs. In all honesty, even the Turbolink PSU shown above is starting to look good compared to this PSU.

Anyways, even with this new driver transformer setup, the KDM PSU was still dead, regardless if I tried to use the onboard SDC2921 or Cyberlink PSU to drive the C945 BJTs. Really, the only new difference with the JNC driver transformer was that the PSU made a slightly louder “tick” noise and the output voltages could jump up to the ~100mV range. But for all practical purposes, the PSU was still dead.

Like I said, I was about to throw the towel after this. I kept checking all components after each test above, to make sure nothing had gone bad, and nothing did. Clearly, however, if the PSU isn't working with external or internal base drive pulses and a replacement BJT driver transformer, something else was hiding from me. I know the JNC PSU driver transformer is good, because that PSU suffered from a single-transistor (with no feedback) 5VSB circuit going bad and killing the DBL494 power circuits.

Eventually, I decided to check the protection diodes across the C945 driver transistors (Q11 & Q12) one more time. The readings (in-circuit) didn't seem too unreasonable, though. The forward voltage drop was slightly low at ~0.29 to 0.3 mV (given they are 1N4148's), but I considered it “passable” due to other circuit components. Meanwhile in reverse direction, the voltage drop was a little over 1.1V across each diode, confusing me that perhaps there is indeed a circuit path somehow through the two 2.7-KOhm resistors connected between the secondary-side Aux. rail and the Bases of Q11 & Q12. Furthermore, when testing these diodes in reverse-bias in resistance mode, I was getting about 1.3 KOhms - which is very close to approximately ½ of the 2.7 KOhm resistors. But once Q11 and Q12 were removed and I re-checked the measurements of these diodes again, it became clear that a circuit path CANNOT exist and they should read open, regardless of those 2.7 KOhm resistors. So I desoldered those diodes and sure enough, one was showing a resistance out of circuit of about 1.x KOhms both ways! Yup, that booger got me!

So let that serve you (and me) as a lesson that component measurements in circuit cannot be trusted, even if things do look pretty normal.

Once I replaced both of these protection diodes (because, why replace one and risk more headache when I can replace both) and soldered back Q11 and Q12… VOILA! PSU was back to life, even with that jurry-rigged JNC driver transformer. Of course, I replaced it with the original KDM driver transformer after this. Sure enough, the PSU continued to work. Finally!

With that said, this KDM PSU is still far from being finished and ready to use in a computer. Obviously, it still needs EMI/RFI filters on the input. But I won't waste any time doing that before testing the PSU with a decent load first (likely by using a Ni-Chrome heater wire.) I only tried the PSU with a light load so far: ~1 Amp load on the 5V rail and 0.18 Amp load on the 12V rail. I have to say, though, I wasn't impressed at all with the voltage regulation - the 5V rail was fine ~5.1V, but the 12V rail was over spec @ 12.74V. Switching the load around (for a ~1.6 Amp load on the 12V rail and ~0.12 Amp load on the 5V rail), the 12V rail was in spec this time @ ~12.3V as was the 5V rail (barely) at 5.21V. At least the 3.3V was OK both times. Still, as I suspected, the lack of coupling between the rectified 5V and 12V rail transformer windings (a better group-regulated design) made the 5V and 12V rails cross-load pretty easily. I'm curious to see how this PSU will do with a real load. I still suspect it won't do too well… but maybe with a bigger load, it will. Who knows!

Anyways, that's all I have for now on this PSU. At least it's back to working condition.

[momaka]

KDMPower MIPC MI-X8775CD [PCB WF-C rev:E] - repaired! (part 1)

I was about to throw the towel on this PSU yesterday. Funny how I said H-bridge PSUs are easy to repair… well, they still are. But sometimes little things can throw you off. With that said, the moral of the story below is that you should NEVER trust in-circuit measurements to be accurate. I already know that, but this one tricked me pretty well.

So what happened? (Oh gosh! Here goes a book again!)

After identifying the blown parts in post #8 above, I dug out the remains of that Raidmax RX-380K PSU from my closet (it's just the PSU PCB with wire harness - case was re-used to provide a home to a nice 250W HiPro PSU that's been installed in another PC for a good few years now.)

Before pulling any parts from it, I decided to draw a partial schematic, similar to the one above for the KDM PSU, so I can compare any design differences and try to figure out what R51 and R53 should be. And here is that:


Going by that, we see the Base pull-down resistors for the primary-side BJTs are 2.7 KOhms each. But I noted there were indeed some differences in the BJT drive design: instead of two 1N4148 series diodes (D11 & D12 or D13 & D14 in the KDM PSU), the Raidmax PSU had only one 1N4148 diode with a 22-Ohm resistor in series. Moreover, the Base biasing electrolytic cap is rated for 1 uF (instead of 10 uF in the KDM PSU.) The secondary side of the driver circuit also had a few differences, but those don't matter as much.

Thus, I was in a dilemma whether to copy the design of the Raidmax PSU by taking parts directly from it and placing them in the KDM PSU, or try to rebuild the KDM PSU how it was originally. Of course, that still doesn't answer the question of what R51 and R53 should be in the KDM PSU (and moreover, the Raidmax PSU is a crap Sun Pro build, so I wasn't too keen on copying it.)

As such, I dug out more junk H-bridge PSUs from storage… namely, these two CWT ISO PSUs:
https://www.badcaps.net/forum/showthread.php?t=39370
https://www.badcaps.net/forum/showthread.php?t=49205

As low-end as they may be, at least they were designed by CWT (and the fully-built versions of these ISO PSUs are actually quite decent.) I looked inside them, and they both had 2.7-KOhm resistors used for the BJT Base pull-down. So I guess 2.7 KOhms it is! Time to start gathering and replacing parts. Heck, I decided to look through my junk pulled parts boxes to see what I have so I wouldn't have to pull parts from the Raidmax PSU. There, I found two 1N4148 diodes (to replace both D12 and D14, just in case there is a mismatch between my pulled 4148's and the cheapo ones in the KDM PSU), two 2.7 KOhm ¼ Watt resistors, and two C945 NPN BJTs to replace both Q11 and Q12 as a pair, just in case. I suspect most of these parts came from a gutless junk JNC PSU I pulled to pieces over a decade ago. Examples of that PSU can be found in these posts, under the names of Meico and Frontier:
https://www.badcaps.net/forum/showpo...80&postcount=2
https://www.badcaps.net/forum/showpo...2&postcount=33

Surprisingly, the only thing I didn't have in my parts bin was the 1-Ohm resistors needed for R50 & R52. But then I found a bunch of MOX ¼ Watt ones on a scrap Panasonic CRT TV board I picked from a TV on the side of the road also around a decade ago (which, BTW, I used parts from to build my first headphone amplifier, which I still use today.) Talk about recycling junk, huh!

Anyways, all BJT drive parts installed and ready to go.

Funny fact: note that the pulled 1N4148 diodes from my crappy JNC actually have a bigger case than the ones originally installed in the KDM PSU. Makes me wonder how low-budget the KDM 4148 diodes must be. Probably some no-name Chinese crap that barely meet the spec sheet of a 4148 diode… if we are even that lucky!
Also note my beautiful handiwork of the resistors with soldered-on extensions leads. Seemed like the easiest way to make those 1/4 Watt resistors fit into the tiny 1/8 Watt spots on the PCB. Whatever, it's a cheapo PSU - no one should care.

Now the last part: the primary BJTs. Rather than busting out my vacuum desolder pump iron again and pulling the entire primary heatsink from the Raidmax PSU, I decided I'll just remove the primary caps, unscrew the BJTs, and remove them one by one. Besides, I wanted to measure the primary caps of that PSU once more (I did that many years ago in-circuit with a MicroESR, IIRC… so I wasn't sure if the measurements were 100% right.)

On that note, here you can see those “330 uF” Metacon caps measured again:
https://www.badcaps.net/forum/attach...1&d=1608943994
Yeah, they really are 200 uF. What a gyp!

I also wanted to remove them to show you this:
https://www.badcaps.net/forum/attach...1&d=1608943994
Ah, don't you just admire that beautiful Raidmax / Sun Pro craftsmanship! Seriously, I have no clue how they got the leads on those transistors to get so crooked. I feel 0% bad about taking parts from this turd-of-a-PSU. Actually, on that note, after taking the primary 13007 BJTs out, I also decided to take the C945 driver transistors. That's when I noticed that one of the driver pins on the KA7500 measured 4 Ohms to ground. This PSU suffered from bad caps on the 5VSB at one point, making the secondary-side auxiliary rail grossly overshoot and burn resistors going to the driver circuit and KA7500 IC… so there's a good chance that IC is toast too. Luckily, the C945 transistors were OK. Ah well, it was a from the factory. Let's not shed any tears.

Back on track… mounted the 13007 BJTs from the Raidmax onto the heatsink of the KDM PSU and test-fitted them, but no bueno! -Their leads were just ever so slightly shorter to go through the PCB on the KDM PSU. Thus, more hacking was needed! I pulled a bunch of dead TO-220 devices from my ultra-uber-junk-bins and clipped their leads - hey even dead parts can be useful for something!!! Soldered those on and this was the result:

It sure ain't pretty, but whatever. I just need the crap to work!

So after everything was installed and ready for a test, I plugged the PSU through a series resistive device (60 Watt incandescent light bulb), in case anything decided to blow. As expected, though, nothing did. 5VSB came up normal, as did the secondary-side auxiliary rail, which I measured around 13V with no load on the 5VSB and about 14V with a 0.5 Amp load on the 5VSB. Conditions could hardly be more ideal. Thus, I shorted PS_ON to GND and…
.
.
.
Nothing?

I tried again a few more times, with and without various small loads on the 5V and 12V rails, just to make sure that wasn't the issue. I also switched my series current-limiting device to a 450-Watt heater from a dishwasher, in case the high-impedance was an issue (can be with some PSUs, as I've found over the years.) But nope! PSU was still dead as a door nail, 5VSB aside. At most, the 5V and 12V would climb to ~10 mV, but that's it.

The first thing that crossed my mind: that SDC2921 IC must have died. After all, one of the driver C945 BJTs attached to it was shorted (likely from the voltage spike that propagated through the driver transformer when the primary BJTs blew.) Things weren't looking too good anymore.

Part 2 coming in a few minutes... I really need to learn how to stay within the 10k char limit, lol.

[momaka]

Re: KDMPower MIPC MI-X8775CD [PCB WF-C rev:E]

When Motorola introduced their Switchmode series BJTs - 2N654x in TO-3 (actually, TO-204) and MJE1300x in TO-220 - they were the first BJTs optimized for use in switchmode power supplies. So they were some of the best at what they did ...... in the late 1970s. Similarly, LM358, et al, were top-notch parts, when National Semi first introduced them, and now they're still too good at what they do to obsolete them.

Yeah, you're right. I should have said it differently. Those parts were indeed the best back when they came out... but today they aren't. Of course, they are still more than good enough, so that's why we probably won't see them get phased out anytime soon. Not to mention their availability and price.

BTW, your SDC2921 is a PWM-supervisor combo IC.

Yes.
A lot of H-bridge PSUs now use similar chips that are essentially "decked out" PWM controllers with built in UV/OV/SC protections. SG6105 is another popular one, as are AT2005b, ATX2005, and WT7514L. Deer/Allied's "chip of the year" (i.e. 2003, 2005, and 2012) PWM controller is another one I think - good luck finding a datasheet for that one, though.

Anyways, that aside, I haven't made any other progress on this PSU yet. Also working on several other old computer stuff right now, so I do whichever one I feel in the mood for. For this one, I just have to pull the parts from the Raidmax PSU.