Computer power supply - repair?

mzeitlin3348

mzeitlin3348

See it and Believe
One of my computers power supply failed. Out of curiosity, I wonder what part typically fails in these units which might be simple to replace (i.e. transformer?/ caps?).

The symptoms are - when the unit is supplied power, the LED on the power supply lights. As soon as I hit the power button to start the computer, the power LED (next to power cord) goes out and an amber/yellow LED lights up on the front panel. Power supply is not working.

I did replace the power supply with another one I had on hand (doesn't fit the enclosure, however) and the computer powered up normally and works. The computer is not worth spending money on (an old one I use for experimenting), but if it is just a simple part, I'll spend a few dollars to fix it.

Thanks
 
Register to hide this ad
If you saw any bulging/leaking caps that might be some clue, but not necessarily the end of the story. You'd need to familiarize yourself with how switching power supplies work and actually diagnose it barring a lucky strike, so to speak.
 
The only thing I've ever had fail is the cooling fan. And that was from buying cheap power supplies that used cheap sleeve bearing fan motors. I put more money into power supplies now, and they don't fail after 18 months like the cheapies. Usually it was the fan, then everything would overheat and the computer would shut down. For me, the circuits were too complicated to bother with, so I just replaced the whole power supply.
 
whoaru99 said:
If you saw any bulging/leaking caps that might be some clue, but not necessarily the end of the story. You'd need to familiarize yourself with how switching power supplies work and actually diagnose it barring a lucky strike, so to speak.
Click to expand...

I was just curious what typically goes wrong with computer power supplies when they fail due to age.
 
Update: I opened the power supply and sure enough there are 3 bulging electrolytic caps with two leaking. Not worth the hassle getting to them to replace. Odds are that's the problem. Everything else looks brand new - especially the large power caps and transformer.
 
whoaru99 said:
If you saw any bulging/leaking caps that might be some clue, but not necessarily the end of the story. You'd need to familiarize yourself with how switching power supplies work and actually diagnose it barring a lucky strike, so to speak.
Click to expand...
Too troublesome if you have an alternative power supply. Check the capacitors and transistor switch if no assess to schematic. You have to pull them off the board to check them -- to much trouble for 50 % chance that is what went south. A lot easier to have schematic to do trouble shooting.
 
I've fixed a bunch that had bad caps. Most of time due to it being some weird proprietary form factor.

And yes fan failure happen allot. I've even swapped fans to get that extra couple years out of em.

In my experience once one gets into higher watt ps units, 600+ watts, the wire bundles and component density and often glue make such repairs near impossible and not worth the time.
 
Eggs and Grannies not withstanding and personal limited experience in this arena.

Computers perform POST [Power On Self Test] when switched on. If all the relevant power lines [3v3, 5v0, 12v0, plus and minus] to the motherboard are not within a small margin the computer will not switch on.
Try searching for POST messages/sounds/lights for your model of computer - you may get a hit that will help.
Failing that - with the power supply out of the computer - try checking voltages on the power lines - one might show up as low which should at least point you in the direction of where to look? Depending on the age of the computer [power supply] you [may] need to ground green wire to get the PS to play.
The tube has some vids regarding troubleshooting/repair - try searching for Power Supply Troubleshooting and Repair Tips. Usual warnings regarding big voltages and fully charged caps if you do decide to open it up - BEWARE!

Hope this helps.
 
SolderIron said:
Cap often fail by dry up and circuit stress. How often do you find bad power transistor in fixing?
Click to expand...

Once in a while that happens too. Or rectifier failures.

Most times I never bother diving deeper if replacing a few caps dont fix it. Most supplies aren't worth putting several hrs of work into.

Also most newer supplies have allot of smd components. So can be a royal pain to test.

For most needs a new one is $80 or less (not 800+ watts). Not worth screwing around a whole lot.
 
kinswad said:
Eggs and Grannies not withstanding and personal limited experience in this arena.

Computers perform POST [Power On Self Test] when switched on. If all the relevant power lines [3v3, 5v0, 12v0, plus and minus] to the motherboard are not within a small margin the computer will not switch on.
Try searching for POST messages/sounds/lights for your model of computer - you may get a hit that will help.
Failing that - with the power supply out of the computer - try checking voltages on the power lines - one might show up as low which should at least point you in the direction of where to look? Depending on the age of the computer [power supply] you [may] need to ground green wire to get the PS to play.
The tube has some vids regarding troubleshooting/repair - try searching for Power Supply Troubleshooting and Repair Tips. Usual warnings regarding big voltages and fully charged caps if you do decide to open it up - BEWARE!

Hope this helps.
Click to expand...

This is all good advice.

I would add that even if a system posts and boots up. I've seen systems shut down or bug out once a load is applied countless times. Think having a video card that needs dedicated power then once in windows a benchmark is run. BAM, down goes the system. Even cpu benchmarks, prime95, can cause this.
 
You must log in or register to reply here.
Back
Top Bottom