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prime
April 11th, 2016, 10:15 AM
Hi all,

I have one of the Schrack 130W 240V XT PSUs that has an odd problem.

Connect it to the mains and load it with a known good MFM hard disk, nothing else and throw the switch and up it spins, measuring the voltage output on the 12V & 5V lines indicates that it is producing the correct voltages there.

Then power the thing down and try and power it up again, and I get no output voltage, but the PSU fan still spins. Wait a couple of minutes and try again and low and behold it powers up fine.

Any idea what the problem could be. This PSU used to work.

Cheers.

Phill.

gertk
April 11th, 2016, 10:27 AM
Bad caps? (Causing a crowbar circuit to activate?)

The fan could be AC powered directly from mains.

Raddit123
April 11th, 2016, 10:31 AM
Hi Phill,

Just a suggestion - A similar thing happened to me with a cheap modern PSU, basically I loaded it too much and it blew (it claimed to be 750W and this was on a 400W system). Strange thing was, when I took it out the case and hooked up a hard disk then powered it on, the disk span up, same thing with the fan on it; however when plugged into the system not a bean. I got a new PSU and it fired up to windows straight away. Anyway back to the point, with mine I think a few caps went + some other stuff. Is it worth taking yours apart and having a look to see if any of the caps have gone (especially if it is an old PSU) or there is any other sign of damage?

Good luck!

Malc
April 11th, 2016, 10:41 AM
Have you tried it without the MFM hard disk attached, ie: no external load ?, does it still exhibit the same symptoms.

Stone
April 11th, 2016, 11:41 AM
Many PSUs of that vintage require a load to start at all.

Malc
April 11th, 2016, 11:57 AM
Many PSUs of that vintage require a load to start at all.

Yes i totally agree, Though I have several Schrack 130W 240V XT PSU's and all of them start with no external load attached, The output voltages are not quite optimal, But not that far off.

prime
April 15th, 2016, 08:56 AM
Just to follow up, it looks like I had the same problem that vossi did in this thread. (http://www.vcfed.org/forum/showthread.php?48683-Repair-of-5160-XT-power-supply)

Namely that the 3300uf 16V capacitor in the centre of the board had gone short circuit. Replacing the capacitor with a 3300uf 25V has brought both PSUs back to life.

I think we can mark this down as a stock fault for the Schrack 130W PSUs :)

Cheers.

Phill.