Blog IndexPosts by TagHome

VAX 4000 Power Supply

Posted <2018-06-04 Mon 23:38> by Aaron S. Jackson.

bnl passed away in January and a month or so before that he put a VAX 4000 in my loft. I've decided it is finally time to try and get it working. So, let's get started…

Despite the fans spinning up, and most of the lights coming on, the DC LED does not light up. That would definitely indicate an issue with the power supply.

The power supply has many layers and is kind of annoying to take apart.

The last image is the 12V module. I don't know much about checking over power supplies, but checking the transistors and MOSFETs seems sensible. After finally getting under the head I lifted up two MOSFETs and saw a terrifying sight.

Oh dear… Look at those wounds! How did that happen. I've ordered some replacements - they will probably explode but at least that will confirm whether something else is wrong.

<2018-06-05 Tue 23:47> Decided to have another look tonight while I wait for the MOSFETs to arrive and came across this filthy cap. I've removed it, sadly no replacement. Gotta wait for some of these to arrive now as well.

<2018-06-19 Tue 11:16> I forgot to update to say that there are still problems after replacing the capacitors and MOSFETs. I also found a dead diode on the +12V output, which I have also replaced. I also stripped off quite a large number of components to clean any corrosion which was still on the board. I'm not completely sure what the issue is yet. More time is needed…

Wanting to leave a comment?

Comments and feedback are welcome by email (

Related posts:

Tags: oldcomputers

Blog IndexPosts by TagHome

Copyright 2007-2022 Aaron S. Jackson (compiled: Sun 2 Jan 00:24:09 GMT 2022)