Power Supply Problem?

  • Thread starter Thread starter John F Kappler
  • Start date Start date
J

John F Kappler

System does not do anything when the start button is pressed, but was
previously running ok.

Whats the easiest way of testing the power supply? (We have a small
circuit tester available).

TIA

JohnK
 
System does not do anything when the start button is pressed, but was
previously running ok.

Whats the easiest way of testing the power supply? (We have a small
circuit tester available).

TIA

JohnK
Click to expand...

Unplug power supply from everything except one HDD, pulling the AC
cord first. Let's hope that one HDD isn't shorting out, but if you
suspect it might be, later repeat the following with it plugged into a
different HDD or an optical drive:

Short the PS_On pin to ground with a paperclip, piece of wire,
whatever, with the AC cord already plugged in. AT that point the PSU
should turn on, it's fan spinning and the HDD spinning too. If you
have a voltage meter you could then check the voltages on each rail.

If the above doesn't turn on the power supply then you need a voltage
meter to check voltage level on the 5VSB pin and PS_On pin.

If the power supply DID turn on with above test, plug it back into the
motherboard and try disconnecting the case front power switch and
manually shorting the power-button pins, to see if the front power
button (or it's wiring) broken.

If there's still no activity, including even a brief spinning of the
power supply fan when you try to turn it on, unplug all non-essential
components from the motherboard, leaving ONLY 1 memory module, CPU,
heatsink fan, video card. Try to turn on system.

If there is STILL no signs of life then unplug power supply from AC,
then unplug from everything else and remove from case. After 10
minutes have elapsed (from being unplugged from AC) open power supply
and inspect it for signs of damage.



Dave
 
Also check PSU board connector for signs of pin damage if you have removed
and reconnected it lately.....
 
John said:
System does not do anything when the start button is pressed, but was
previously running ok.

Whats the easiest way of testing the power supply? (We have a small
circuit tester available).
Click to expand...

To test an ATX PSU:

First, disconnect everything from the power supply (including MB.) Plug
AC cord into the rear of the PS. IF the PS has its own rocker on/off
switch, turn it ON. There should be +5v on pin 9 of the 20 pin connector
(+5vsb, usually a violet wire.) There should be >0.8v on pin 14 (PS-ON,
usually a green wire.) This is from an internal pull-up to the +5vsb.

Connect PS power leads to 1 or 2 IDE HDs (for a load). Jumper pin 14
(PS-ON) to pin 13 (ground, black wire.) At this point, fan in PS should
start spinning, drives should spin, and + 5/12v, -5/12v, +3.3v, and
+5vsb should be present at 20 pin connector.

Disconnecting pin 14-13 jumper should turn supply back off.

Additionally:

When your system fails to start, what is the voltage on pin 9? If it is
less than 4.75v, either a) the logic on your motherboard is shorting
b) your +5vsb is under powered, or c) your PS is bad. It is
most likely a combination of b) and c).

If your +5vsb is OK, measure pin 14 of the PS/MB connector. If it is <0.8v
(and the +5vsb is OK), the power supply should be on. If pin 14 is <0.8v,
the +5vsb is OK, and the PS is OFF, the PS is bad. If pin 14 is >2.0v, the
power supply is being told to stay OFF by the MB. If depressing the front
panel ON/OFF switch does NOT lower pin 14 to <0.8v (and the +5vsb is OK),
then the problem is NOT the power supply, but rather MB related.

Good luck.
 
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