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Old 02-28-2003, 01:23 AM   #1
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Default Repairing a Power Supply

Hi all,

So tonight I fired up a 75A power supply -- that I had bought used online -- with my dyno for the first time. End result? Smoke from the PS. Now, whenever I plug the PS in, it trips the circuit breaker. Bonus for me!

The PS is a 75A unit from a company called Todd Engineering, which, surprise of surprises, is no longer in business. Double bonus!

Does anybody know if there is a place out there I could go to get something like this repaired, or am I pretty much out of luck? I know a bit about electronics but not nearly enough to fix something like this; I opened it up but I can't even figure out which part is fried.

All I know is, I am bummed!
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Old 02-28-2003, 02:01 AM   #2
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Default Re: Repairing a Power Supply

Quote:
Originally posted by futureal
Hi all,

So tonight I fired up a 75A power supply -- that I had bought used online -- with my dyno for the first time. End result? Smoke from the PS. Now, whenever I plug the PS in, it trips the circuit breaker. Bonus for me!

The PS is a 75A unit from a company called Todd Engineering, which, surprise of surprises, is no longer in business. Double bonus!

Does anybody know if there is a place out there I could go to get something like this repaired, or am I pretty much out of luck? I know a bit about electronics but not nearly enough to fix something like this; I opened it up but I can't even figure out which part is fried.

All I know is, I am bummed!
Repairing a PSU is no joke and no easy job....it a loop...very hard to troubleshoot.....Please becareful.
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Old 02-28-2003, 02:16 AM   #3
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I wont claim I'm an expert in this, but here goes:

I believe that we're talking about a switched mode PS?

Usually, theres a transformer between the input section and the output section. This transformers job is to ensure there's no mechanical/electrical connection (dont know the right english word) . The transfer is done magnetically. Now, if you can identyfy those parts, you might have a chance to do it yourself. Take out all FET's and capasitors and throw in some new. It's a shotgun method, but it should could be done. But of course, I dont know how many components there's on the secondary side.

I dont know if this is much of a help, I've only tried it on a small model on 7,5 amps.
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Old 02-28-2003, 10:18 AM   #4
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Quote:
Repairing a PSU is no joke and no easy job....it a loop...very hard to troubleshoot.....Please becareful.
what he said is true.. it's dangerous...

1st. DO NOT TOUCH ANY OF THE HI VOLTAGE CAPACITOR TERMINAL.. probably there is still a charge inside.. to confirm check with DVM... if there is still a voltage stored in it.. discharge it...

2nd. If there is a smoke... it'll make you life a bit easier... use a sniffing method.... try to sniff around the components like MOSFET or IC... look carefully... there might be a burnt mark or crack...and replace if any...

3rd. Could also be caused by a inrush current resistor blown up... look for a ceramic resistor that have a very small resistance...0.1 something ohm...check..

4rd. If the PSU is very old... you might consider replacing the Hi Voltage capacitors..to a newer type that has a lower ESR and meant for switching PSU... these caps will degrade and leaky after a while...

well... that's all I can contribute... hope this helps.. lol

JUST BE CAREFUL....
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Old 02-28-2003, 11:09 AM   #5
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Yea, I wasn't really planning on doing too much digging around the thing myself. I was more looking for an avenue for repair.

Like I said, I know enough about electronics to use my Fluke to figure out what still has voltage and drain it where appropriate, so I don't kill myself. And unfortunately the "sniff test" didn't work so well in this case, although I haven't really taken anything out yet.

Since repairing it is probably beyond my meager abilities, I will probably wait to send it or give it to somebody who knows what they are doing.

In the meantime, though, if anybody knows any good websites that talk about the inner workings of an AC->DC power converter, post 'em here and I'll do some reading...
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Old 03-01-2003, 05:36 AM   #6
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Quote:
Originally posted by futureal
Yea, I wasn't really planning on doing too much digging around the thing myself. I was more looking for an avenue for repair.

Like I said, I know enough about electronics to use my Fluke to figure out what still has voltage and drain it where appropriate, so I don't kill myself. And unfortunately the "sniff test" didn't work so well in this case, although I haven't really taken anything out yet.

Since repairing it is probably beyond my meager abilities, I will probably wait to send it or give it to somebody who knows what they are doing.

In the meantime, though, if anybody knows any good websites that talk about the inner workings of an AC->DC power converter, post 'em here and I'll do some reading...

This one's good.

ESP

It's rod elliott's. he has a 20amp (can be scaled upwards) power supply that uses transformers which are more rugged than switching power supplies. There are also some HI-FI schematic diagrams there. yummy.
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