Help with 3 ATX PSUs

**Pentium4** · 06-08-2015, 01:29 PM

Re: Help with 3 ATX PSUs

It's dead as a rock,as it doesn't give ANY voltages. Any ideas?

Have you checked fuse, cold joints, little primary side caps? Is there a "hot" spot around the 5VSB? Did the fan seize?

This one is a Sun Pro (TB-1.3 marking on PCB and AT-2005B marking on PCB) and it's quite weak (20A rectifiers on all rails) but it works. Voltage on 3.3v is a bit high (3.49V) but I think it's gonna be good for something after mods. This one has PI coils as opposed to my old 350W one.

I think I had one of these. The one with the really thin heatsinks? When I turned mine on with just a paperclip, I also noticed that the 3.3V rail ran very high. Also could be a sign of failing output caps on that rail or a high resistance minimum load resistor.

ARE PICTURES COMING?!

**kaboom** · 06-08-2015, 10:18 PM

Re: Help with 3 ATX PSUs

Originally posted by Dan81

Alright,I've got 3 PSUs from a friend,as he wanted me to test them.
First,here are the models:

1.Eurocase 200XA1/250XA1

This one is just a case swap of some 250-300W Linkworld (LEC marking was my giveaway that it's a Linkworld) with a ghetto-crafted rocker switch on a plate. It's dead as a rock,as it doesn't give ANY voltages. Any ideas?

If no 5VSB, check for open/burned/blown resistor feeding the ~320V into the standby TX. It'll be from 4.7 to 47 ohms. Also check for a shorted aux switching transistor. If you see that, the current sense (if "two-transistor" ckt) resistor in the emitter or source (BJT/FET, respectively) is probably open too. If that has opened, the resulting voltage on the top of what was the resistor will backfeed into the 2SC945/1815 and destroy it.

It's likely the standby and aux caps went bad and it tried to run away. There should be a 6-6.2V zener across the 5VSB output, and it's probably shorted, with the surrounding board discolored. The 5VSB rectifier may also have been hot.

Here's what could have happened:
Caps go bad and VSB starts going high
Ripple increases, so zener clamps just peaks of ripple at first

Caps get worse, now zener is clamping the increased VSB, attempting to hold it down. This greatly increses the standby load, adding to the heat and degradation of the caps.

One or more caps open(s) completely, resulting in either gross overvoltage (zener shorts) or backfed peaks to switching transistor (no caps on VSB side to "swallow" them) cause it to short, resulting in cascade failure. After the aux switching transistor shorts, excess voltage is fed into the 945/1815 via the current sense node, the shorted switching transistor opens either/both the current shunt or that "fusible" from the 320V supply.

Of course, make sure both main filter caps have equal voltage across them. In older doubler supplies, which get 320-340 VDC from 120VAC, a faulty rectifier can result in only one of the caps charging!

**Dan81** · 06-08-2015, 10:50 PM

Re: Help with 3 ATX PSUs

Originally posted by Pentium4

ARE PICTURES COMING?!

Nope since I had to give my camera to a relative for a period of time and I don't know when I get it back. Anyways I checked the PCB for anything strange but it was clean,almost brand new,save for a few spider webs on the secondary caps.

kaboom- everything looks brand new in the Eurocase PSU. And no,the fan didn't seize (a Yate Loon BTW)and any other components looked fine. There isn't any voltage coming out of it: no 5v,no 3.3v,no 12v and no 5VSB. Basically all rails give 0V on my DMM.

**kaboom** · 06-08-2015, 10:59 PM

Re: Help with 3 ATX PSUs

Originally posted by Dan81

Nope since I had to give my camera to a relative for a period of time and I don't know when I get it back. Anyways I checked the PCB for anything strange but it was clean,almost brand new,save for a few spider webs on the secondary caps.

kaboom- everything looks brand new in the Eurocase PSU. And no,the fan didn't seize (a Yate Loon BTW)and any other components looked fine. There isn't any voltage coming out of it: no 5v,no 3.3v,no 12v and no 5VSB. Basically all rails give 0V on my DMM.

Does anything on the primary side look burnt, or otherwise "stressed?"

Check for ~160V across each large cap, and ~320V across both in series.

**momaka** · 06-08-2015, 11:11 PM

Re: Help with 3 ATX PSUs

Well, time to get dirty with that DMM then ^ .

Start at AC input and keep going deeper. First check fuse. Then bridge rectifier (or 4 diodes... we all know how cheap PSUs are

). Next, transistors on primary heatsink. Then the large resistors. Then diodes... you get it. You need to start checking components. "Looks fine" means nothing. I have seen both a resistor go open circuit and a diode go short circuit without any visible sign or heat damage. This was in two power supplies for completely different equipment.

Obviously, the most important thing is first to get 5VSB going. So don't waste too much time checking components for the main PS. That will come later if there is a problem.

**Dan81** · 06-09-2015, 12:58 AM

Re: Help with 3 ATX PSUs

Originally posted by kaboom

Does anything on the primary side look burnt, or otherwise "stressed?"

Check for ~160V across each large cap, and ~320V across both in series.

Nothing burned. The PCB is clean in all areas.

momaka - Only one of them (the broken Linkworld in EC case) has a bridge rectifier. The Sun Pro and the L&C both have 4 diode treatment. I do have some PSUs I can harvest parts from (a 250W Bestec,a iMicro,a Codegen and some dead Deers).

Also,checked the Eurocase. All appear fine. I'm going to scrap it for parts and see if I can get the Deer to work. As far as the friend is concerned,I'm going to give him my dualcore's PSU and a KME PX-450 PSU and mod the Sun Pro,then mod the other Deer,since it seems my modded Deer seems to exhibit the same problem as the Eurocase,even though it worked fine last time I tried using it.

**momaka** · 06-09-2015, 07:04 AM

Re: Help with 3 ATX PSUs

Like I said in my previous post, "appears fine" and "nothing visually burned" means nothing. You have to take the PSU board out of the case and start checking components one by one with the multimeter.
If you want to learn to repair PSUs, that's how you start.

Other than that, I don't know how else we can help you. You are neither telling us what you checked so far (component-wise), nor are you providing pictures (which I understand is not possible at this time).

**RJARRRPCGP** · 06-09-2015, 07:55 AM

Re: Help with 3 ATX PSUs

Originally posted by Dan81

So,any ideas on why the Eurocase PSU is dead as a fly?
The PCB has no sign of any discolouration or burn marks or anything like that.

Fixed!

**Dan81** · 06-09-2015, 10:21 AM

Re: Help with 3 ATX PSUs

Originally posted by RJARRRPCGP

Fixed!

So,any ideas on why the Eurocase PSU is dead as a rock?

Fixed again!

**Pentium4** · 06-09-2015, 04:39 PM

Re: Help with 3 ATX PSUs

So, everything "looks" fine on the top. Have you at least pulled the board out to analyze the underside? We all know about cheap PSU soldering "quality"

Have you tried any of the tests that kaboom suggested?

**RJARRRPCGP** · 06-09-2015, 06:20 PM

Re: Help with 3 ATX PSUs

Originally posted by dan81

fixed again!

lol

**Dan81** · 06-11-2015, 10:58 AM

Re: Help with 3 ATX PSUs

Originally posted by Pentium4

So, everything "looks" fine on the top. Have you at least pulled the board out to analyze the underside? We all know about cheap PSU soldering "quality"

Have you tried any of the tests that kaboom suggested?

Pulled board,looked fine.

Seems there was a dead resistor on the secondary (hidden away in a jungle of 12v wires) but by the time I realized that I just said "damn it,I already have a working Linkworld that I can mod" and chucked it in my pile of dead PSUs for parts.

Maybe I haven't told you,but I have made a pile of dead PSUs. Most of them are gutless wonders,however there's a Delta Electronics 180W PSU in there. It has PFC.

As for the 2 Deers I have right now,you may be able to help on this one with ideas what to check. I have to scrap the one I got for free (a JNC LC-B350ATX,3.3V rectifier burned,bleeder resistor burnt near primary cap and a lot more) as it's absolutely dead (not even 5VSB comes in) but as for my modded one,it seems it's the same except this one gives 5VSB (measured about 5.14V) but no other voltages. This happened after changing the heatsinks with some thicker ones.

**momaka** · 06-11-2015, 10:01 PM

Re: Help with 3 ATX PSUs

Originally posted by Dan81

Pulled board,looked fine.

Seems there was a dead resistor on the secondary (hidden away in a jungle of 12v wires) but by the time I realized that I just said "damn it,I already have a working Linkworld that I can mod" and chucked it in my pile of dead PSUs for parts.

Even if the PSU is gutless, it is still worthwhile to troubleshoot it and get it working. That way you get more experience with fixing power supplies.

One time I fixed this Sun Pro that I knew from the start was a complete waste of time.

Basically, after keeping it in storage for a year, half of its output caps bulged, including on the 5VSB. When I plugged it in, the 5VSB started acting all weird even with the tiniest of loads and a resistor giving power to the PWM chip started smoking. Now this is something I have seen before, but never knew what the cause was. Turns out, bad caps on the 5VSB could make the secondary side auxiliary rail go super-high and kill the PWM chip. In my case, it didn't get to that since I caught it in time.

In the end, I recapped that PSU with total crap caps that appeared (and passed my spark test) fine. And what do you know? Both 5VSB and secondary side aux. rail stabilized immediately. So I learned about some interesting failure modes of the 5VSB that could kill the PWM chip. And as luck would have it, someone posted a question here on BCN just a few months after trying to fix their PSU from the same problem.

So in short, you can learn some great lessons even from the cheapest and crappies of power supplies. IMO, fix it and then use it for scrap parts.

**Dan81** · 06-11-2015, 10:36 PM

Re: Help with 3 ATX PSUs

Originally posted by momaka

Even if the PSU is gutless, it is still worthwhile to troubleshoot it and get it working. That way you get more experience with fixing power supplies.

One time I fixed this Sun Pro that I knew from the start was a complete waste of time.

Basically, after keeping it in storage for a year, half of its output caps bulged, including on the 5VSB. When I plugged it in, the 5VSB started acting all weird even with the tiniest of loads and a resistor giving power to the PWM chip started smoking. Now this is something I have seen before, but never knew what the cause was. Turns out, bad caps on the 5VSB could make the secondary side auxiliary rail go super-high and kill the PWM chip. In my case, it didn't get to that since I caught it in time.

In the end, I recapped that PSU with total crap caps that appeared (and passed my spark test) fine. And what do you know? Both 5VSB and secondary side aux. rail stabilized immediately. So I learned about some interesting failure modes of the 5VSB that could kill the PWM chip. And as luck would have it, someone posted a question here on BCN just a few months after trying to fix their PSU from the same problem.

So in short, you can learn some great lessons even from the cheapest and crappies of power supplies. IMO, fix it and then use it for scrap parts.

The Linkworld I scrapped was not worth it,and I was forced to scrap the Sun Pro due to lifted solder pads on the secondary heatsink. That,and I can buy another Sun Pro exactly the same but with a real ERL-35 transformer. Still,any help with the modded Deer? It gives 5vsb but nothing else.

**momaka** · 06-11-2015, 11:26 PM

Re: Help with 3 ATX PSUs

Originally posted by Dan81

Still,any help with the modded Deer? It gives 5vsb but nothing else.

What happens when you short PS_ON to ground? Any ticking noises? Faint short duration buzz? Fan "kick" for a split second?

If not, check secondary side auxiliary voltage. Then check the primary transistors and their base-drive circuitry (2-3 resistors and 2 diodes). Also the main PS driving transistors (and corresponding diodes) on the secondary to see if they are shorted. Probably hard to point out that stuff without a picture to you, though.

**Dan81** · 06-12-2015, 02:05 AM

Re: Help with 3 ATX PSUs

Originally posted by momaka

What happens when you short PS_ON to ground? Any ticking noises? Faint short duration buzz? Fan "kick" for a split second?

If not, check secondary side auxiliary voltage. Then check the primary transistors and their base-drive circuitry (2-3 resistors and 2 diodes). Also the main PS driving transistors (and corresponding diodes) on the secondary to see if they are shorted. Probably hard to point out that stuff without a picture to you, though.

Here's a picture from the thread with the modded Deer:

**Dan81** · 06-13-2015, 10:05 AM

Re: Help with 3 ATX PSUs

Back to this thread,I've got good and bad news:

"Bad" news - I had to scrap the JNC and the ANS PSUs because both were completely dead.
"Good" news - I traded with a friend of mine a Bestec ATX-250-12Z PSU (out of a HP DX2200) and a Rexpower PX400 for a Premier LC-B400ATX (which is an exact replica of my old ANS LC-B350ATX,did some mods on it such as AC rocker switch in place of monitor plug (built a bracket from a piece of metal and screwed it into the monitor plug of the PSU),PI coils on the secondary,SBL2045PT for 12v (again,Deers work fine with this on the 12v,got a 20100 somewhere tho) and X cap on the primary,last thing is better rectifiers for 3.3 and 5v and common mode choke) and a Gigabyte GA-8IPE1000 (even though BIOS shows "Intel 865PE AGPset for GA-8IPE1000-G F1").

Will post pics when I get my camera and finish modding it. Forgot mentioning,I've installed some 470uf Canicons in place of the 330uf primaries. Yes,I know,Canicon sux,but the YC (Saturn logo) primaries it had were INCREDIBILY tiny,while those Canicons are quite fat. (in diameter ofcourse).

In the ending,have a laugh at what the label claims:

Code:

PREMIER MODEL:LC-B400ATX (PR17XA at the bottom,anybody know what this means?)
AC INPUT
VOLTAGE - 115V~ 230V~
CURRENT - 10A / 6A
FREQUENCY - 60~50Hz

DC OUTPUT
3.3V - 28A (the rectifier is actually 10A!!)
5V - 40A (rectifier is 10A,seen some with 16A rectifiers)
12v -17A (had D-O-B (diodes-on-bracket),rectifier is now 20A)
-5v - 0.3A
-12v - 0.8A
5vSB- 2A

5V & 3.3v COMBINED MAX 220W.
5V & 3.3V & 12V COMBINED MAX 380W
TOTAL OUTPUT MAX 400W.

Help with 3 ATX PSUs

Help with 3 ATX PSUs

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