31 Mar
2008
31 Mar
'08
10:02 p.m.
Hi
Its not test gear that's the problem its access to the board. My Tek
465 will trigger on single pulses with no problem.
However whilst it's recommended that the the first CPU board (the 8330)
be in slot 2 (The front panel is in No1) its not mandatory. So I can
move the boards back a bit and get to the front of the 8330.
Manual I have, (very good) Schematics also (Awful) so bad I may even
redraw at least the 8330. I have an A0 HP plotter so its easy to do
drawings.
Rod
-----Original Message-----
From: cctech-bounces at classiccmp.org
[mailto:cctech-bounces at classiccmp.org] On Behalf Of Tony Duell
Sent: 31 March 2008 22:52
To: cctalk at classiccmp.org
Subject: Re: Looking for a M8330 or a couple of SN74194's
Not only did Cricklewood have them, but they arrived Saturday morning.
I'm even luckier in that I live near enough to Cricklewood Electronics
that I can pop over there and pick the chips up the same day ;-)
That effected a partial fix.
The timing generator is a string of four bit shift registers clocked
with 20Mhz.
OK.
Various combinations of their outputs are used to set
and reset
bistables made out of cross coupled 7440's.
As the problem I'm fixing is you can't load memory, which is a one
shot operation, its slow old work.
I don;t know what test gear you have, but I find a simple logic probe to
be more use than a 'scope for this sort of problem. The former can
easily detect narrow pulses that are difficult, if not impossible, to
see on a non-storage 'scope. Of course an 'Advanded Logic Probe' as HP
called the LogicDart is even nicer, but...
Do you have the maintenance manual? Not the printset (schematics), but
the book which is a low-level circuit description? It's well worth
reading!.
I would have thought it wouldn't be too hard to keep on hitting the DEP
key and seeing what, if any Omnius signals are generated. And then
totrace back the missing one(s).
[...]
I also return all systems to working order. Apart from
a couple of
VT420's with ticking SMPSU's everything I have restored runs. (Three
Any reason you';ve not fixed those? Ticking SMPSUs are often quite
simple to fix, maybe just dried-up capacitors.
-tony
1 Apr
1 Apr
12:30 p.m.
Hi
Its not test gear that's the problem its access to the board. My Tek
465 will trigger on single pulses with no problem.
However whilst it's recommended that the the first CPU board (the 8330)
be in slot 2 (The front panel is in No1) its not mandatory. So I can
move the boards back a bit and get to the front of the 8330.
All Omnius slots are the same, and in an 8/e backplane, AFAIK all slots
are plain Omnibus.
The only time the top connectors are used on the M8330 is if you have the
EAE board set installed, I think. If you do, take it out for the moment
(you don't need it when trying to sort out a timing generator problem).
You can then put the M8330 in whatever slot you want.
An extender board is useful, but by no means essential :-).
Another trick that's worked for me in the past if I can't re-arrange the
boards and don't have an extneder is to solder a hnadful of wires to
useful testpoints on the board and put it back in the cardcage. Then
probee the free ends of the wires (make sure they don't short to
anything!). Normally 2 or 3 iterations of doing that will get me to the
faulty chip.
Manual I have, (very good) Schematics also (Awful) so bad I may even
redraw at least the 8330. I have an A0 HP plotter so its easy to do
drawings.
DEC scheamtics have the odd error on them (I've heard it claimed said
errors are deliberate, either to stop the machine being copied, or as
copyright traps on the diagrams themselves). They're also somewhat
unconventionally drawn (flip-flops may appear to have 4 outputs!), but
I've got used to them. I must say that if I need to re-draw a sechematic,
I use pen and paper, not a CAD system...
-tony
6 p.m.
Tony Duell wrote:
DEC scheamtics have the odd error on them (I've
heard it claimed said
errors are deliberate, either to stop the machine being copied, or as
copyright traps on the diagrams themselves). They're also somewhat
unconventionally drawn (flip-flops may appear to have 4 outputs!), but
I've got used to them. I must say that if I need to re-draw a sechematic,
I use pen and paper, not a CAD system...
A year and a half ago I was playing with a PDP-8/e and trying to get an
EAE working with it. I ended up needing a later version M8330. My
original boards were rev 1 and the EAE didn't work until about rev 3.
The drawings I found online were WAY different than the boards I had.
For the EAE, it looked like there were some serious timing issues, so
the later board revisions were quite significant.
So, if your boards don't match the drawing rev, don't expect there to be
a match.
-chuck
2 Apr
2 Apr
3:07 p.m.
A year and a half ago I was playing with a PDP-8/e and
trying to get an
EAE working with it. I ended up needing a later version M8330. My
original boards were rev 1 and the EAE didn't work until about rev 3.
The drawings I found online were WAY different than the boards I had.
For the EAE, it looked like there were some serious timing issues, so
the later board revisions were quite significant.
So, if your boards don't match the drawing rev, don't expect there to be
a match.
This issue is by no means limited to the PDP8/e, or indeed DEC.
On the 11/45, there was a amjor change to one of the boards which added
an extra latch on some signals, and needed a backplane mod (an extra
clock signal) for it to work. Please don't ask how I found that ont...
And HP did similar things. On the HP11205 for example (RS232 interface
for the 98x0 machines), there were major changes betwee Rev A and later
veriosn. The latter had a little modification to get it to work in the
9830, and extra circutiry added to generate a delay after a carriage
return. The 2 boards are nowhere near the same! (I have something I call
an 'A.5'. I've don the 9830 mod, just a cut trace and jumper, but not
tried to add the delay circutiry).
-tony
6108
days inactive
6109
days old
3 comments
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participants (3)
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ard＠p850ug1.demon.co.uk -
chd_1＠nktelco.net -
RodSmallwood＠mail.ediconsulting.co.uk