30 Apr
2011
30 Apr
'11
1:23 a.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Rob Jarratt
Sent: 30 April 2011 00:25
To: 'General Discussion: On-Topic and Off-Topic Posts'
Subject: RE: H7140 PDP11 PSU
> -----Original Message-----
> From: cctalk-bounces at classiccmp.org [mailto:cctalk-
> bounces at classiccmp.org] On Behalf Of Tony Duell
> Sent: 29 April 2011 22:02
> To: cctalk at classiccmp.org
> Subject: Re: H7140 PDP11 PSU
>
> >
> > I took the plunge and put in the CPU modules (M7133 and M7134) into
> > the PDP11/24. The machine powered up and the DC ON light came on,
> > suggesting voltages were in tolerance. So I connected a terminal and
> > got
> an ODT prompt.
> > I then tried to run a basic diagnostic (using the ODT command
> > 165000G). It came back to the prompt and I was just entering another
> > command when I heard a vague click and the machine powered off. I
> cannot power it on now.
> > Previously after connecting it to the mains I would hear a slight
> > click, but I don't even hear that now and turning the key will not
> > even start the fans running.
>
>
> Oh $deity...
>
> I am actually not too suprised about the fans if nothing else is
working.
As I mentioned
earlier, the fans run off a 36V DC output from the
memory switch-mode PSU. So if everythign is dead, the fans don't run
either...
However power is getting to the big capacitors because I can see
that with my multimeter, so it is not the external fuse or the
circuit breaker I think. Presumably some internal fuse has gone, I
will leave it to discharge
I don't remember any inernal fuses...
I am going to have to look at the prints, but from what I remembr,
there's soem control circuiry on the leftmost PCB in the PSU unit.
This is powered form a small SMPSU circuit. I think I would chekc that
that is gettign first. Pehaps solder som wires ot the power pins
of one of the TTL
chips inthe control section, put the PCB back in place, conenct said
wires ot a voltmeter, attempt to power up and see if you get 5V to
power said TTL chip.
-tony
I will add some diagnostic wires to the board as you suggest, I don't
remember a lot about TTL chips, is there a convention about which are the
power pins?
In the meantime someone else told me that the click I would hear when
connecting to the mains (before switching it on with the key) was some of relay. I don't hear that anymore, would that
help to isolate the
problem at
all?
Regards
Rob
I have extracted the leftmost board, which is a 5413605, according to
printset that is a "bias and interface" board. Looking at where it is
mounted in the PSU, it *appears* to be connected to the fan spade
connectors, so would be involved in powering the fans (the motherboard
printset would seem to confirm that). There is a 74LS00 chip on it to which
I will attach wires to Vcc and Ground so I can test if for power. I followed
the Vcc track on the back of the board and it does not appear to go to the
boards "backplane" connectors. I tried to read the printset to see which
pin(s) on the connector the power comes in on but I don't understand the
conventions about which pin is pin 1 on the connectors, so I can't at the
moment add wires for that. I will go ahead and add wires to the 74LS00 in
the meantime.
Regards
Rob