Got stiffed on a bad PSU. Need to repair it

J

janas19

[H]ard|Gawd
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Jan 20, 2012
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So I bought a PSU on Craigslist from a seller as part of a bundle deal, everything else worked but the PSU was bad. It's a Corsair TX750. I plugged it in and once or twice it makes a crackling noise, but won't turn on. Seller won't return phone calls, I think he's going to dodge me and pocket the $30 I paid for it.

I've worked around computers for years and I'm comfortable with soldering, but never on a power supply unit. I understand that multimeter readings can be used to determine what circuit/component might be bad. I will also do a visual inspection and maybe see if anything is obviously burnt.

Any tips on repairing this PSU? Also, can anyone recommend an inexpensive multimeter? I'm thinking just a $20 MM should do, unless there's a reason to pay more.

Thanks!
 
Maybe going through Corsair to RMA it? I've had issues in the past with Corsair not being able to help me with RMA because I didn't have an invoice/sale receipt. Try contacting them and see.
 
Don't bother repairing PSUs. They're generally not designed to be user serviceable, especially not by noobs who don't already have a multimeter. Don't open the PSU and just do an RMA.
 
Last time I had a PSU doing that all it was was a loose spade connector that when from the AC power plug to the circuit board. A quick crimp of the spade connector to make it tight fixed it.

The crackling noise is what I was getting as well.

I've recapped a decent number of PSUs as well and never had them fail after replacing bad caps with better quality ones.

As for a cheap MM, if you have a Harbor Freight in your area, you can get one for about $10. Absolutely no reason to pay more than that unless you are going to be using it all the time for work. And if you fry it, you are out only a few dollars.

They even have coupons for a free one with any purchase every once in a while. I generally end up with 3-4 a year that I end up giving away.

That being said.. I pretty much never try to even figure out what has gone bad in a power supply IF it is anything but caps or a bad connection. If an actual component like a transistor or transformer has gone bad it is likely that it has taken out other components as well. Simply not worth it to repair.
 
If you don't all ready own a multi meter I would stay away from opening a PSU people have died tearing into PSUs blindly
 
Crackling is usually arcing on the high voltage side.
A trace may have 'unstuck' itself from the PCB, or became broken. It's something a visual inspection could show.
BUT.
Friendly reminder: A 1000uF capacitor loaded to 230 Volts is 26 Joules of energy. That's two blasts from an air gun - all going in through your fingers. Best case scenario - you can lose feeling in your hand.
 
michalrz said:
Crackling is usually arcing on the high voltage side.
A trace may have 'unstuck' itself from the PCB, or became broken. It's something a visual inspection could show.
BUT.
Friendly reminder: A 1000uF capacitor loaded to 230 Volts is 26 Joules of energy. That's two blasts from an air gun - all going in through your fingers. Best case scenario - you can lose feeling in your hand.
Click to expand...

So you just discharge the PSU by turning it on when it is not plugged into the wall.

Bleh.. I've been opening up PSUs since I was about 12... shorted something out and fried a power transistor in an AT PSU. Ended up fixing it myself.

I've probably harvested parts out of over 200 PSUs at this point. I used to take them all apart, harvest the fans, maybe some wire, and also save the casing for scrap metal.

I used to do the same with CRT monitors and TVs. Never once got shocked.

I actually don't understand how you can get shocked as long as you make sure to discharge everything by turning it on when it is not plugged in. That is standard practice to discharge the caps on electronics.

Only time I have been shocked by a cap was when I was taking apart a broken camera. The flash cap was apparently still charged. It left two pinpoint sized black marks on my finger and didn't feel too good. Scared the crap out of me when it happened though.

See Here for PSU capacitor safety.. basically as long as you leave it alone for a few minutes it is safe to open.

http://www.overclock.net/a/capacitor-safety-in-power-supplies
 
cyclone3d said:
So you just discharge the PSU by turning it on when it is not plugged into the wall.

Bleh.. I've been opening up PSUs since I was about 12... shorted something out and fried a power transistor in an AT PSU. Ended up fixing it myself.

I've probably harvested parts out of over 200 PSUs at this point. I used to take them all apart, harvest the fans, maybe some wire, and also save the casing for scrap metal.

I used to do the same with CRT monitors and TVs. Never once got shocked.

I actually don't understand how you can get shocked as long as you make sure to discharge everything by turning it on when it is not plugged in. That is standard practice to discharge the caps on electronics.

Only time I have been shocked by a cap was when I was taking apart a broken camera. The flash cap was apparently still charged. It left two pinpoint sized black marks on my finger and didn't feel too good. Scared the crap out of me when it happened though.

See Here for PSU capacitor safety.. basically as long as you leave it alone for a few minutes it is safe to open.

http://www.overclock.net/a/capacitor-safety-in-power-supplies
Click to expand...

I have some fun projects going that utilize voltages at around 500V with capacitances up to 7000uF.
I too have never got shocked, I always treat them with respect, mind the wires, check their status with a voltmeter, discharge with lightbulbs and all that.

But, perhaps selfishly, I don't extend this approach as a recommendation to others. You just never know what the exact circumstances are.
I've seen people spray isopropyl alcohol at the PSU PCB, I also know there are people with pacemakers.
Or people who, upon receiving a slight jolt, would recoil and bang their head on some furniture. You just never know...

I utilize the same concept with pharmaceuticals. I never lend as much as a paracetamol to anyone without first asking if he or she has already taken it in the past.

I know what you're talking about, though. It is possible to drain the thing and then literally lick the PCB, but... what if, y'a know? :D
 
cyclone3d said:
Last time I had a PSU doing that all it was was a loose spade connector that when from the AC power plug to the circuit board. A quick crimp of the spade connector to make it tight fixed it.

The crackling noise is what I was getting as well.

I've recapped a decent number of PSUs as well and never had them fail after replacing bad caps with better quality ones.

That being said.. I pretty much never try to even figure out what has gone bad in a power supply IF it is anything but caps or a bad connection. If an actual component like a transistor or transformer has gone bad it is likely that it has taken out other components as well. Simply not worth it to repair.
Click to expand...

I agree, I won't spend too much time on it. But I did open it up after giving it time to discharge, and noticed brown stains/goo all over the daughter board where the PSU fan leads attach. My guess is there are leaking caps, could this liquid be causing the leads to short?

I'm going to buy a can of compressed air and a can of electrical cleaner and spray all the dirt and liquid out. That might show me where the bad caps are.
 
The day and age of repairing a psu are long gone.

Just pick up a new one with a warranty. $30 isn't bad, add another 15 and you can get a nice efficient psu.
 
janas19 said:
I agree, I won't spend too much time on it. But I did open it up after giving it time to discharge, and noticed brown stains/goo all over the daughter board where the PSU fan leads attach. My guess is there are leaking caps, could this liquid be causing the leads to short?

I'm going to buy a can of compressed air and a can of electrical cleaner and spray all the dirt and liquid out. That might show me where the bad caps are.
Click to expand...

The brown stuff is most likely just glue that has discolored. Do you see any stuff coming out of the tops of the caps? The tops will also most likely be split open if they are leaking. I have never once seen a cap leak from the bottom which is sealed by rubber.
 
cyclone3d said:
The brown stuff is most likely just glue that has discolored. Do you see any stuff coming out of the tops of the caps? The tops will also most likely be split open if they are leaking. I have never once seen a cap leak from the bottom which is sealed by rubber.
Click to expand...

If you're working inside a PSU and find the yellow adhesive has turned brown/black, it's a good idea to remove it. when whatever adhesive they use degrades like that, it becomes conductive and can cause shorts. Some PSUs use silicone, but I find that stuff can still become conductive.
 
janas19 said:
I agree, I won't spend too much time on it. But I did open it up after giving it time to discharge, and noticed brown stains/goo all over the daughter board where the PSU fan leads attach. My guess is there are leaking caps, could this liquid be causing the leads to short?

I'm going to buy a can of compressed air and a can of electrical cleaner and spray all the dirt and liquid out. That might show me where the bad caps are.
Click to expand...

Goo and brown stains are often just glue that was put in there to dampen any vibrations. They often become brown because they pick up filth from the air going through them.
If you smoke (not necessarily just tobacco) then the adhesive will become dirty quite quick.

It's a bit brutal, but I've also seen bugs get into power supplies because they're nice and warm. Then they become electrocuted or hit by a fan blade and umm... leave residue.
One of my friends is a farmer, and I have personally seen a dead mouse on his nice (then) 6600GT. The card couldn't into 3D anymore after that. Spiders inside PSUs are a common sight.

And like a broken record - be careful with the liquid cleaners. Some are alcohol based, can cause a short, which causes a spark which can lead to a bonfire@home. It's not likely, but it's possible. I've seen some sh**t.
 
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