Repairing a PC. PSU : id Components

Thread Starter

spike1947

Joined Feb 4, 2016
223
Hi

I am having an attempt at repairing a Computer 600W PSU, a sort of exercise to see if I can.
First is I am trying to id as many the components on the board as possible before I start to test , not really sure which ones would be best to test first , as I would have to de-solder each one to test , or could I test any that are attached ! .
Anyway some are fairly easy to id, but some not so, to start there is a, what looks like a resistor of some sort, the markings from what I can see are “5° C V1” it is sleeved ! , underneath on the PCB one of the pins is marked “Ropp” !
 

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dl324

Joined Mar 30, 2015
11,897
First is I am trying to id as many the components on the board as possible before I start to test , not really sure which ones would be best to test first , as I would have to de-solder each one to test
That's not the standard way to troubleshoot circuits.

We generally try to locate bad components with the circuit powered. You either start at the beginning and work forward until you find something not functioning correctly; or you start at the end and work back until you find something that is functioning correctly.

Be careful. Dangerous voltages are present in computer power supplies and they don't have a transformer to isolate you from line voltage.
 

MrAl

Joined Jun 17, 2014
7,849
Hi

I am having an attempt at repairing a Computer 600W PSU, a sort of exercise to see if I can.
First is I am trying to id as many the components on the board as possible before I start to test , not really sure which ones would be best to test first , as I would have to de-solder each one to test , or could I test any that are attached ! .
Anyway some are fairly easy to id, but some not so, to start there is a, what looks like a resistor of some sort, the markings from what I can see are “5° C V1” it is sleeved ! , underneath on the PCB one of the pins is marked “Ropp” !
First, what is the failure symptom?
 

MrAl

Joined Jun 17, 2014
7,849
Hi
It won't fire up, the fan just blips then nothing, no obvious signs, all Caps look ok, nothing looks burnt out, no smell anywhere .

Spike
That does sound like the electrolytic caps going bad.
Do you see any bulging or any brown stuff at the bottom of the larger electro caps?
Sometimes it is hard to see you have to look really carefully.
You dont usually smell anything though.

The caps are the ones on the output of the supply that connect to the wires that form the output like the +12v and +5v lines.

When these caps go bad, the power supply turns on for a short time, then turns right off, because one of the voltage or current detection mechanisms detects a fault. When the filter cap is bad, it no longer filters the pulses that feed it so there are very high and very low levels occurring at the output and that triggers the over voltage trip setting that the control chip or other chip senses. It then shuts off the output. The time it takes to shut off could range from several hours to less than a second. As the caps get worse with time, the time it takes to shut down decreases.
 

Thread Starter

spike1947

Joined Feb 4, 2016
223
That does sound like the electrolytic caps going bad.
Do you see any bulging or any brown stuff at the bottom of the larger electro caps?
Sometimes it is hard to see you have to look really carefully.
You dont usually smell anything though.

The caps are the ones on the output of the supply that connect to the wires that form the output like the +12v and +5v lines.

When these caps go bad, the power supply turns on for a short time, then turns right off, because one of the voltage or current detection mechanisms detects a fault. When the filter cap is bad, it no longer filters the pulses that feed it so there are very high and very low levels occurring at the output and that triggers the over voltage trip setting that the control chip or other chip senses. It then shuts off the output. The time it takes to shut off could range from several hours to less than a second. As the caps get worse with time, the time it takes to shut down decreases.
[/
Thanks for that , will have a closer look , all the tops seem to be ok .
Spike
 

Ramussons

Joined May 3, 2013
890
Hi
It won't fire up, the fan just blips then nothing, no obvious signs, all Caps look ok, nothing looks burnt out, no smell anywhere .



Spike
Have you put a minimum load on the +5V output? Most of the ATX PSU's will not come on without a minimum load.

The 6800a is the PWM controller and WT7527 is the Voltage / Current monitor.
 

Thread Starter

spike1947

Joined Feb 4, 2016
223
Have you put a minimum load on the +5V output? Most of the ATX PSU's will not come on without a minimum load.

The 6800a is the PWM controller and WT7527 is the Voltage / Current monitor.
Hi Ramussons
No haven't , should of though ! , will try that .
PS: Have short ( PS-ON) pin 16 to Ground to test it on the bench ! , you weren't thinking that were you ! .
tks
Spke
 

MrAl

Joined Jun 17, 2014
7,849
Hi Ramussons
No haven't , should of though ! , will try that .
PS: Have short ( PS-ON) pin 16 to Ground to test it on the bench ! , you weren't thinking that were you ! .
tks
Spke
A load is usually mandatory i assumed you had a load.
If i remember right, i used a 5 ohm power resistor on the +5v line to test mine.

BTW, i had an LCD TV with fluorescent tube backlight do the same thing to me. It would turn on then turn off, or it would take many tries to get to turn on. It turned out the electrolytic caps were bad in that too. After replacing them with quality units, the TV functioned fine again.
It was a brand called "AOC" which these days stands for something entirely different (ha ha).
 
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