29 Mar
2020
29 Mar
'20
3:30 a.m.
Rob Jarratt via cctech wrote:
I would be interested. I have an VAX400/300 with such an working again
PSU, Changed Capacitors two years before..now it works. A friend gave me
another PSU with a similar fault, changed capacitors as before on the
other one..but no luck at all. It still powers down shortly after
switching on. Yes..thats the most ugly PSU Design I ever saw..and I'm
interested in schematics or parts of them..
Regards,
Holm
--
Technik Service u. Handel Tiffe, www.tsht.de, Holm Tiffe,
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-----Original Message-----
From: cctech <cctech-bounces at classiccmp.org> On Behalf Of Robert
Armstrong via cctech
Sent: 29 March 2020 02:29
To: cctech at classiccmp.org
Subject: H7874 power supply
Does anybody have a maintenance print or service manual for the DEC
H7874?
This is the power supply used in the BA4xx and R400x cabinets. As you
might
guess, I have one that tries to power up but
shuts down after a second.
Probably a bad capacitor (or several), but this thing is ridiculously
complicated
and not all that easy to disassemble, either.
I'd like to be able to
trouble shoot
it rather than just firing the proverbial parts
cannon at it. FWIW, none
of the
electrolytic (of which there are many) have
obviously failed - no leaking,
no
bulges, etc. Of course, that proves fairly
little.
This PSU is a real problem, as you say, complicated and hard to disassemble.
I had one that didn't work, if I remember correctly in the end I had to get
another one. I have a second machine with this PSU which has an intermittent
problem and shuts itself down after a few minutes if it hasn't been used for
a while, but a subsequent power up sees it work for as long as I need it.
It looks like I reverse engineered the schematic of the 12V output board. I
don't know if that would be of any use? How correct it is I don't know.
Regards
Rob