DECstation 5000/133 power supplies dead (H7826)

Rob Jarratt robert.jarratt at
Sun Oct 1 17:33:00 CDT 2017

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Seth
> Morabito via cctalk
> Sent: 01 October 2017 22:38
> To: cctalk at
> Subject: DECstation 5000/133 power supplies dead (H7826)
> All,
> I have two DECstation 5000/133s here with dead power supplies. I've done
> some basic troubleshooting on both, and I've recapped the other, but they're
> still dead dead dead.
> I don't see any obviously blown components, and the fuses are fine, but several
> of the caps I replaced WERE leaky. I inspected for bad traces but found none.
> So far it looks like the high voltage side is totally fine, but the low voltage side is
> completely dead. No activity. Switching transistors SEEM fine, but I haven't
> pulled them to check them out of circuit.
> Is anyone intimately familiar with the H7826? Any obvious failure modes I
> should check?

The H7826 is the next one that I have to repair, mine is in a really bad way though, lots of leaks and corrosion, and I have not even started to look at it yet. If there is nothing happening on the secondary side then I would have expected the switching transistors to be the prime suspects, best remove them for testing as you suggest. 



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