VOGONS


First post, by kotel

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Hi,

Recently I recapped my Excellent power model IT ATX 300 PSU (all 2200uF and whole 5vsb circuit caps). Applied power to it and 5vsb was 5.1v while ps_on 4.9v. Since everything was in spec I shorted the ps_on.
I was surprised to see that it dies after a split second. All I hear is a slight fan twitch. 5vsb is still generated. Other lines discharge fast so that would mean they are also good.
I am unsure where to look so I'll ask here if anybody has any ideas where to go next.

"All my efforts were in vain...
Let that be my disappointment."
-Kotel

Reply 2 of 6, by Unknown_K

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I generally use a Power supply tester that shows voltages for each channel and PG status.

Collector of old computers, hardware, and software

Reply 3 of 6, by kotel

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konc wrote on 2025-02-04, 09:08:

Do you have anything connected to have some load, or you are just turning it on? If this is the case add some load like an old hdd

There are what look to be 3.9ohm load resistors on 5v/12v. Might try some load before I go replace the smaller caps.

Unknown_K wrote on 2025-02-04, 09:11:

I generally use a Power supply tester that shows voltages for each channel and PG status.

PG rail... I forgot to check it. Huh.

"All my efforts were in vain...
Let that be my disappointment."
-Kotel

Reply 4 of 6, by kotel

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Okay yeah, there's no PG line. It's completely dead. Out of all the dead/broken power lines I saw PG is the one I least suspected...
I have no idea what might be the cause now.

"All my efforts were in vain...
Let that be my disappointment."
-Kotel

Reply 5 of 6, by kotel

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Replaced most of the smallest caps (aside from two near the middle transformer) and all that did was make the fan move for a tad bit longer.
Any ideas where to go next?

"All my efforts were in vain...
Let that be my disappointment."
-Kotel

Reply 6 of 6, by kotel

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I have done some probing on the secondary diodes and here are the results:
D17 resistance:
GND - both anodes show 0 ohms, kathode 14ohms
5V - both kathodes 14ohms, anode 0 ohms
-12V - all pins 450K ohms
12V - all 1.4M ohms
3.3V - anodes 6.8ohms, kathode 21 ohms

D14 resistance:
GND - 0omhs everywhere
5V - kathode 730K ohms, anodes 14ohms
-12V - anodes 450K ohms, kathode 900K ohms
12V - kathode 0ohms, anodes 1.4M ohms
3.3V - anodes 6.8ohms, kathode 0ohms

D13 resistance:
GND - 6ohms kathode, all anodes 0ohms
5V - anodes 14ohms, kathode 21ohms
-12V - all 450ohms
12V - all 2M ohms
3.3V - anodes 6.8ohms, kathode 0ohms
It's wierd how I got on some lines completely 0ohms (like d14 to gnd).
Now my repair knowledge is kinda limited and I'd like to ask if someone who repairs these PSU's knows of those readings are in spec?

"All my efforts were in vain...
Let that be my disappointment."
-Kotel