2 Apr
2022
2 Apr
'22
7:41 p.m.
It was quite a struggle to separate those nylon
connectors, is there a
trick to it?
You mean the Mate-n-lok's? Not really; just make sure the catch is released.
What did you do about DCLO? (Oh, I think I see the answer, below.... looks
like you're relying on the pullup on K3...)
When I powered on, the CPU LEDs did not light up.
Two of them ('0' and '1') are just bits in a special register, and thus
only
do anything when the bootstrap code fondles them. When you get ODT running,
you can amuse yourself turning them off and on manually! :-)
I did notice that the CLK LED flickered on briefly
when I powered it
off.
Interesting. Not sure exactly what we can deduce from that; but interesting.
I put a scope probe on TP1 (p152 of the PDF), there
was no activity,
the pin remained high.
Yes; the signal there (MCLK H) is more or less the same one that drives the
'CLK' LED (MCLK L); so no big surprise there. Still, that reduces the problem
space to a small part of K1.
The problem now is that I expect I will need to probe
various pins to
find out what is going on. But I don't have a Unibus extender and I am
reluctant to remove the backplane. From what I can tell in the
Technical Manual you can't install the CPU in other slots
Basically right; the backplane and CPU are designed to have it go in slot 1.
It _might_ work in other MUD slots, with some loss of functionality (e.g.
slot 2 doesn't have grant lines; MUD slots won't have the 'UNIBUS Map board
pesent' line - pin FE1, on K11, UB TO MA VIA UBMAP) but I wouldn't want to
chance it, there might be a clash.
I am forced to tack solder probe wires to the chips,
which works but is
time consuming. Any other ways?
Sorry, I don't have any experience to suggest any; too well supplied with
extender cards, so I've never had to resort to alternatives!
I *think* I have found something. There could be a
fault in E52 (sheet
K6, p157 of the PDF). While K6 BUS DCLO L is +5V, I am measuring K6 BUF
DCLO H at an average 1.64V
Yeah, that's wrong. E52 is bad, and will have to be replaced.
(From the +5V on BUS DCLO, I guess you're relying on the pullup? DCLO on the
UNIBUS, with the resistor network on the M9302, should be about 3.5V - but now
I'm confused, even with the P/S connector unplugged, it should still be 3.5V
or so. Oh well, it's late, the brain is powering down... :-)
The 'unused' gate in E52 is the one that the added wires from the ACLO ECO went
to;
I wonder if it was damaged by the -15V, somehow?
logical 0 output should be 0.4V max
Which is what you should be seeing.
I also measured K6 BUF DCLO L to be always low,
suggesting it thinks
the K6 BUF DCLO H is a logical 1.
Yup; and that definitely explains why the clock isn't running - BUF DCLO L is
clearing E41 on K1.
Anyway, you'll have to replace E52 (which will be a bit of a pain, with the 3
ECO eires tacked to it). The DS8641 is an old chip, no longer in production, so
the usual suppliers may not have it, but there are some on eBait.
Noel