Fun with fixing I-Micro power supplies

[ben7]

Re: Fun with fixing I-Micro power supplies

I finished putting the parts in my last "decent" IMicro pc board. Plugged her in and the 5vsb came up just fine. Used a paper clip to short the green wire to ground to turn it on, and it went off like a sparkler on the fourth of July. Multiple popping sounds, lots of sparks, and some smoke before blowing the fuse. Not too sure if I will be able to resurrect it! Not sure why it went, but it was "just another cheapo pos power supply".

I don't see any burnt spots.

[momaka]

Re: Fun with fixing I-Micro power supplies

I finished putting the parts in my last "decent" IMicro pc board. Plugged her in and the 5vsb came up just fine. Used a paper clip to short the green wire to ground to turn it on, and it went off like a sparkler on the fourth of July.

You need to build yourself a incandescent dim bulb tester. It should help you save A LOT of fuses from blowing in the future.
Details:
https://www.badcaps.net/forum/showpo...4&postcount=70

[Pentium4]

Re: Fun with fixing I-Micro power supplies

Did the switchers blow? What does the underside look like?

[everell]

Re: Fun with fixing I-Micro power supplies

Here is the last picture I took of this IMicro before powering it up.....before it blew.....

[everell]

Re: Fun with fixing I-Micro power supplies

I don't see any burnt spots.

OK......here are the pictures of the "burnt spots".You can see that several resistors and diodes are burnt. Both switching transistors were shorted. One of the switching transistors has smoke showing damage to it. The transistor without any smoke on it had even more severe damage.....when I took it apart the insulation pad had smoke damage under the transistor. The back of the transistor at the mounting hole had arc damage. The insulation "button" showed some melting and was fused to the transistor mounting hole. Most likely an insulation breakdown, short, and arcing on this transistor was the main culprit for this failure. Yes, it did take out the fuse.

[everell]

Re: Fun with fixing I-Micro power supplies

So.....a few parts replaced here and there and back for more testing. This picture shows the repaired pc board. Initial power up and the 5vsb is again working. Voltage across the main capacitors measured 332 volts. PS-on switch turned on and nothing. At least it didn't blow up! No fan twitch, no outputs, nothing. Serious troubleshooting to follow..........

[ben7]

Re: Fun with fixing I-Micro power supplies

So.....a few parts replaced here and there and back for more testing. This picture shows the repaired pc board. Initial power up and the 5vsb is again working. Voltage across the main capacitors measured 332 volts. PS-on switch turned on and nothing. At least it didn't blow up! No fan twitch, no outputs, nothing. Serious troubleshooting to follow..........

Well the short circuit might have burnt out a winding in the main transformer or the driver transformer.

[kaboom]

Re: Fun with fixing I-Micro power supplies

replace the two 2sc945/1815s and any 4148s on the cold side of the driver tx

[Behemot]

Re: Fun with fixing I-Micro power supplies

It's fun Plus, not every computer needs a lot of watts. If it's a Core 2 with no video card, and a single hard drive, it doesn't need a lot of juice.

I can understand all that. But taking the whole picture, when this thing has tragic efficiency no matter what you do, and that bloody time you put into it, it is just so wasted. In two years some better PSU with higher efficiency will pay itself on electricity. Maybe even several times.

Oh BTW everell, seems that you are cheaping it out, too That wire jumepr does not look like thermistor to me

[goodpsusearch]

Re: Fun with fixing I-Micro power supplies

Wait.

Taking semi decent psus and turning them to decent 300 watters is fun and entertaining and you can use them in a usual core duo machine in the end.

On the other hand, when the psu is badly designed, for example having space on secondary for only 1 output cap per rail and no coil, then why bother? Who would trust even a Pentium 4 on a psu like that?

[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

[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!

[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.

[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!

[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

[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.

[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

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.

[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

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.