Fun with fixing I-Micro power supplies

[ben7]

Re: Fun with fixing I-Micro power supplies

If you're right across the transformer...

Not much will blow PCB traces, what sort of "ampacity" do they have?

It also depends on how "antiquated" or cheapened the wiring is. Like #14 for a loop length of 100 feet, y'know, cause "it's good for 15 amps." Or if things were backstabbed or not.

Those long, all-#14 ckts aren't likely to deliver more than ~200A fault current. I measured one with a 12.5A heater. Voltage dropped from 122 to 114 = 0.64 ohms. 122/0.64= ~190A bolted.

Then there's I2S- those little filter chokes, with their small wire, often survive, at least for one "accident." Microwaves often use small wire on the "monitor" or "short switch;" all this has to do is carry the load til the fuse blows. These are often on much better circuits (SABC) and the fault current is from 300-600A- the magnitude is higher, but that fuse is gone in just a few cycles.

Hence the high-interrupting ceramic fuse specified for MWOs.

Dan is from Romania, where they use 240V ... not 120V :P

[kaboom]

Re: Fun with fixing I-Micro power supplies

Fault currents CAN be hundreds or even thousands of amps ... they WILL blow out PCB tracks as well, fairly often. :P

If you're right across the transformer...

Not much will blow PCB traces, what sort of "ampacity" do they have?

It also depends on how "antiquated" or cheapened the wiring is. Like #14 for a loop length of 100 feet, y'know, cause "it's good for 15 amps." Or if things were backstabbed or not.

Those long, all-#14 ckts aren't likely to deliver more than ~200A fault current. I measured one with a 12.5A heater. Voltage dropped from 122 to 114 = 0.64 ohms. 122/0.64= ~190A bolted.

Then there's I2S- those little filter chokes, with their small wire, often survive, at least for one "accident." Microwaves often use small wire on the "monitor" or "short switch;" all this has to do is carry the load til the fuse blows. These are often on much better circuits (SABC) and the fault current is from 300-600A- the magnitude is higher, but that fuse is gone in just a few cycles.

Hence the high-interrupting ceramic fuse specified for MWOs.

[ben7]

Re: Fun with fixing I-Micro power supplies

I don't think that's really possible since it's just 2 wires wrapped around a ferrite bead.

Fault currents CAN be hundreds or even thousands of amps ... they WILL blow out PCB tracks as well, fairly often. :P

[Dan81]

Re: Fun with fixing I-Micro power supplies

Oh, and make sure the EMI filter choke hasn't gone open-circuit now too!

I don't think that's really possible since it's just 2 wires wrapped around a ferrite bead.

[ben7]

Re: Fun with fixing I-Micro power supplies

ASSuming it's not any of the semis...

Maybe you put the common mode choke in 90 degrees out, putting one coil across the line and the other across the input to the supply.

The ones with the base can be off and still put in- dead short.



Depending on your PCB, L and N will be reversed; just be sure to put one coil in series with each current carrying conductor.


That fuse cracked because you inadvertantly made a bolted fault.

Yes I second that, only a very severe short circuit (low resistance) would make a fuse do that, UNLESS, it was just a cheap fuse with a low interrupt rating xD

Make sure you have installed the EMI choke the right way, and be sure to double check things like the bridge rectifier and switching transistors for shorts, just in case
Oh, and make sure the EMI filter choke hasn't gone open-circuit now too!

FYI, it would be best to use a "dim-bulb tester" for this. You just use an incandescent lightbulb in series with the PSU to limit the current. If there is a short circuit, the bulb will glow brightly, but it is much less likely for components to be damaged.

[Dan81]

Re: Fun with fixing I-Micro power supplies

ASSuming it's not any of the semis...

Maybe you put the common mode choke in 90 degrees out, putting one coil across the line and the other across the input to the supply.

I used a wire choke and installed horizontally (parallel with board) on the desired place on the board (my PSU was the same as the last iMicro everell fixed. However,mine came with a bridge rectifier from factory)

BTW,the only parts missing were 2 PI coils,a common mode choke (which courtesy of my stupidity made it blow because I should have installed it vertically [parallel with the primaries and bridge rectifier ) and a X cap (yellow and rectangular caps IIRC). Maybe installing the choke vertically and replacing the fuse will fix it? What do you think?

[kaboom]

Re: Fun with fixing I-Micro power supplies

completed the AC filtering

ASSuming it's not any of the semis...

Maybe you put the common mode choke in 90 degrees out, putting one coil across the line and the other across the input to the supply.

The ones with the base can be off and still put in- dead short.



Depending on your PCB, L and N will be reversed; just be sure to put one coil in series with each current carrying conductor.


That fuse cracked because you inadvertantly made a bolted fault.

[Dan81]

Re: Fun with fixing I-Micro power supplies

Looks like "33" or possibly even "28" size.

It's a real 33 size. I have a Intex 28-er and the 28 is even smaller than what those iMicros use.

BTW,I just had an PSU exact to that iMicro blow its fuse after I installed PI coils and completed the AC filtering that now awaits fixing,along with the Intex 28-er that is an candidate for some lil' modding.

The cause for blowing isn't exact,but I think it's because I tried securing the AC filtering choke with super glue,which if I'm not mistaken it's conductive,and from that fuse the was heard. It's literally CRACKED. I also discarded my Deer PSU - by now my rule is it's not worth anything UNLESS it's an Allied. (Allied PSUs are the more "beefier" versions of L&C/Deer PSUs)


Until I fix it I installed my old Key Mouse built Rexpower PX-400 into my system. Blows quite warm air after an certain time but I don't think it's gonna blow - maybe it's powering an A64 AM2 CPU but most of this PC is low power (1TB HDD,GT210[8400GS],1.50GB DDR2 and as I said a Athlon 64 3200+ single core) At least it has an bridge rectifier - strange thing,all SG6105 based PSUs I've had,they all had an bridge rectifier - even my Linkworld-built Powerlink PSU!

[momaka]

Re: Fun with fixing I-Micro power supplies

I am simply NOT convinced that you will ever get 400 watts out of that smaller transformer.......whereas that so called "terrible" Bestec WILL hold 250 watts.

Even 250W would be pushing it for that small transformer of the I-Micro, especially considering the fact that it is running at a lowly 34 KHz. It is labeled as a "ERL35" transformer, but it is definitely not, I can tell you that. Looks like "33" or possibly even "28" size. Meanwhile, the Bestec's proper "35" transformer should be good for up to 300-350W sustained.

So yeah, you can tell if a PSU is crap straight away by its main transformer. If it's "33" and H-bridge, forget about doing anything more than 250W continuous... if even that, because if the output caps are not up to the job (and they likely won't be), then prepare for ripple waves on the output larger than a tsunami .

[joshnz]

Re: Fun with fixing I-Micro power supplies

Very nice thanks for sharing.

[everell]

Re: Fun with fixing I-Micro power supplies

One final observation I would like to make concerning the IMicro power supplies can be seen in this picture. On the left is the smaller IMicro main switching transformer, on the right is a Bestec main switching transformer pulled from a 250 watt Bestec ATX-250 12E/12Z series power supply. I measured the switching frequency of the IMicro which was a slow poke 34 Khz. Not sure about the Bestec.

I am simply NOT convinced that you will ever get 400 watts out of that smaller transformer.......whereas that so called "terrible" Bestec WILL hold 250 watts.

I have had fun playing with the IMicro power supplies, but I have had even more fun working with the Bestec series. In my opinion, Bestec also has much better circuit design.

[momaka]

Re: Fun with fixing I-Micro power supplies

Intersting that the KA7500 chip got blown too. I guess the voltage spike through that middle driver/feedback transformer must have been huge.

[everell]

Re: Fun with fixing I-Micro power supplies

Back to the IMicro that blew up.......kaboom was right. Both driver transistors were shorted. One of the four diodes in that circuit was leaky, but all four were replaced. Still nothing.

Next I replaced the pwm chip a KA7500B. The output transistors in the chip were shorted to ground and shorted to each other. Now it comes up working again. Voltages with no load are 12.00 volts, 5.14 volts, 3.36 volts, and 5.20 volts standby.

I hooked it to my Biostar M6VLQ Pentium 3 test motherboard. Works fine. As I type this final analysis of this repair, I am listening to some soothing classical music using Audacious on Linux Ubuntu 10.04. Sweet dreams.

[Behemot]

Re: Fun with fixing I-Micro power supplies

I got aprox. half of that, so far Even though mine are mostly good units, can I count one good for two PoS?

[everell]

Re: Fun with fixing I-Micro power supplies

For those that may have missed the attic pictures, I will repost them They were taken several months ago, and a bunch more have been added to the collection.

[Pentium4]

Re: Fun with fixing I-Micro power supplies

TBH, I don't think everell fixes them for a profit.

Definitely not. Have you seen his attic?

Keep up the good work everell

[ben7]

Re: Fun with fixing I-Micro power supplies

TBH, I don't think everell fixes them for a profit. At least that is the idea I am getting. It's more of an interesting exercise, to challenge yourself.

I conclude that working on a variety of power supplies has helped me to learn the difference between a good and bad quality power supply. I have improved my electronics repair skills by working on computer power supplies. I can talk intelligently about them with others. I can stand my ground in arguments, even though I sometimes lose! I have also learned about esr and how to determine quality of capacitors. So much I have learned.

Same here!

[Behemot]

Re: Fun with fixing I-Micro power supplies

I understand all that…but than you can clearly tell it's PoS after opening it, you don't need to waste several days working on them, no?

You know why technicians do not reopair these craps? Because their time has higher value than even such repaired PSU, not mentioning a new one. Doing so is clear loss. The world is so competitive they cannot aford loosing time with PoS nobody will pay for. For me there is a thick line what is worth while, and what is not. Good old (and mostly heavy) PSUs which only have bad caps can still find some use and have some value. Hell I've just repaired old 250W Hipro which could possibly deliver 500 W and used it for Atom system (Gigabyte GA-GC330UD) even though I thought I would never get rid of such low-power (and still quite +5 V heavy) unit. BTW it has DC-DCed +3,3 V rail from +5 V.

Guy wanted as cheap PC as possible using some of his parts. I picked up the stuff I can trust will work for the warranty period and more. I could have used his PoS power supply he brought, but…I don't even want to open that thing to clean it from dust (and believe me, it is full of it). Not mentioning recapping it. It is the same effort to repair that Hipro and this PoS, so +- the same money (in both cases I am doing half of it for free). But I would rather repair decent 150W Hipro built-like-a-tank than average PoS I cannot relly on even with japanese caps. When I am to cover a PC with warranty, made from used parts (which I lately try to avoid completely if it is newer than Socket 939 because that newer HW drops like flies), I need to completely trust every screw in that, otherwise if something gets bad, it is net loss for me with these already minimum margins.

[everell]

Re: Fun with fixing I-Micro power supplies

About seven years ago, I asked myself, why do computer electronic technicians merely remove four screws and unplug a few connectors, then throw away a computer power supply without even opening it up and looking inside to see what is wrong with it. Something that was very puzzling to me.

When most things are broke, an attempt is made to fix it. You would think that even a power supply has some value....after all, someone paid good money for it. Even the many IMicros that I have looked at.

I found the Badcaps website and decided to look into this matter, and learn what was wrong with these bad power supplies. I also decided to learn how to fix them.

I went to a local computer store. The salesman asked if he could help me. I said yes, I am looking for a power supply. The salesman asked what kind. I said......one that is broke. You should have seen the expression on his face! I explained that I was looking for a bad power supply so that I could learn how to fix them. Buying a new power supply that worked wouldn't help me. So he gave me a few bad power supplies that were laying around the shop.

I thought that learning how to fix ANY bad power supply would be a worthwhile experience. My first repair experience turned out to be a Bestec ATX-250 12E, the motherboard killer. Since I didn't know any better, I made the repair, even did some engineering modifications (the 5vsb circuit with DM311), and made my first post on this forum. Wow, what a firestorm I caused. Nobody repairs Bestecs.....they are all pos power supplies! But my repair and modification has resulted in a good reliable power supply. The computer I am using right now has one!

The other thing I learned is the difference between good and bad power supplies. I admit, some I have worked on deserved to be trashed. But consider this. The computer that I was using for a flight simulator had a RaidMax power supply. It also helped many of the capacitors on my mother board to start leaking and bulging. Once I learned, I got rid of that RaidMax in the flight simulator computer, and replaced the capacitors on the mother board, and didn't crash the flight simulator as often.

I conclude that working on a variety of power supplies has helped me to learn the difference between a good and bad quality power supply. I have improved my electronics repair skills by working on computer power supplies. I can talk intelligently about them with others. I can stand my ground in arguments, even though I sometimes lose! I have also learned about esr and how to determine quality of capacitors. So much I have learned.

As for this thread, I have learned that IMicro power supplies are not high quality and have very little potential for repair. I have been playing with three of them that have some potential, but I would not trust them in a computer which I would want to be reliable. Two of them are now working. The third I am still learning from, and I will probably get it running before I quit.

Please don't get the idea that I am repairing an IMicro power supply to be a good, efficient, reliable power supply. I was only trying to find out why so many end up in the trash. In conclusion, even a Bestec ATX-250 12E is a jewel compared to what I have found in the assortment of IMicros I have worked on. If someone has found an IMicro power supply and is considering it for a repair project, please read this thread and save yourself the trouble. Go find a Bestec 12E and have fun fixing it!

Now, if any salesman asks me......why do so many IMicros fail.....I can tell him, in my opinion, it really is a pos!

[Per Hansson]

Re: Fun with fixing I-Micro power supplies

i dont understand why anybody would spend any time on these things.
i would just keep the wire-ended fuse and any thermal pads and bin the rest.

And why would anyone repair a $50 mainboard?
It's a learning experience above all else for me atleast.

Edit: oops, really old quote I realized now, but still it stands, this whole site is dedicated to fixing stuff that most people just throw out because they have no idea and or interest in learning to fix it