[rescue] Decstation 5000 Power Supply

[Michael Dombrowski]

As I've mentioned on this list, I recently picked up a Decstation 5000/200 and was mid-way through Ultrix install when the system powered off and wouldn't come back on. I opened up the H7878A power supply, but don't see any obvious faults. I'm slowly working through it, but I don't have any experience repairing switching power supplies, so this will likely take some time.
As a temporary measure, I ordered a beefy 5v power supply and a -12/+12v buck boost converter. Unfortunately, I'm not able to boot. The power rails all are steady, and thermal imaging does not reveal any suspiciously hot areas. There are two other connectors from the power supply to the logic board: warning and POK. I've tried various combinations tying these to ground or +5v without success. Does anyone know the expected behavior of these circuits? I can find references for older Vax-en, but not for the Decstation. 

thanksmike
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sunhelp.org/pipermail/rescue_sunhelp.org/attachments/20240531/fc2e2aa5/attachment.html>