28 Aug
2014
28 Aug
'14
3:08 p.m.
If it actually made a 'bang' sound the most likely culprit is an
electrolytic capacitor. A visual inspection should find it, although I've
known them to fail pretty amazingly leaving the case intact except for the
circle on the top where the plates came flying out and landed somewhere
remotely.
The system is waiting for P_OK (power OK) before it will fire up, and the
fans are on the non-mains side of that PSU as I recall. Is it the BA23
case? (most common case) there was an issue with the power distribution
harness on those where DEC used several wires in parallel to carry the 5V
current. Except they were not all the same length and the short one would
some times vaporize. The 'fixed' harness you can see all the wires are the
same length which makes it harder to tuck in behind the back plane but it
doesn't blow up.
--Chuck
On Thu, Aug 28, 2014 at 1:19 PM, Robert Jarratt <robert.jarratt at ntlworld.com
wrote:
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:
cctalk-bounces at classiccmp.org]
On Behalf Of Matt Burke
Sent: 28 August 2014 20:07
To: cctalk at classiccmp.org
Subject: Re: Mysterious rtVAX 1000 Failure
On 28/08/2014 18:53, Robert Jarratt wrote:
power
There are two outputs from the PSU that I
don't fully understand, one
is P OK, I am guessing that means *something* is OK, but not sure
what, power perhaps, but what power?. The other is called LTC, I have
no idea what that one means. Can anyone enlighten me?
'P OK' is indeed power OK. This signal will be asserted once all the supply outputs have reached their normal
operating voltage. The Qbus
devices
will be held in reset until this signal is
asserted.
'LTC' is the mains derived line time clock (50hz here in the UK).
Have any of the internal fuses (or circuit breakers) blown? Don't replace
then
until you find the real problem. I would probably
start by checking the
bridge
rectifier and main switching transistor for
shorts.
Matt
I can't find any fuses. There is a circuit breaker, but it doesn't seem to
have tripped (it would be sticking out, right?). I notice that the light in
power switch comes on when I turn it on, if it was the fuse/circuit
breaker,
I expect even the switch's light would not come on.
There are a number of candidates for the main switching transistor, I
think.
Is there a printset somewhere? I have never been able to find one, and it
would help in identifying components.
Regards
Rob