VAXstation 3100 power supply

Dave Wade dave.g4ugm at
Mon Jun 8 09:30:17 CDT 2020

This is just generic advice based on recent experience. I would replace all electrolytic caps. I had some test pretty good, but PSU worked after I replaced them. Also check all the rectifier diodes as well, and I have had an opto-isolator fail.

> -----Original Message-----
> From: cctech <cctech-bounces at> On Behalf Of Peter Hicks via
> cctech
> Sent: 08 June 2020 15:10
> To: cctech at
> Subject: VAXstation 3100 power supply
> Hello
> I have a couple of VAXstation 3100s - a M38 which boots but has no output
> on the console port, and another model which has corrosion on the
> motherboard and a PSU which doesn't power up correctly.
> The voltage on all of the M38 PSU's pins is OK except for pin 7 (brown) which
> is +3.5v to +5.25v DC and is floating at about 0.6v with reference to ground.  I
> suspect this is why the console port doesn't work (and the LEDs on the read
> suggest a RAM problem so I can't tell which chip is faulty), so I've set about
> troubleshooting.
> Does anyone have any suggestions above and beyond replacing capacitors?
> Peter
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