PDP 11/24 - A Step Backwards

[Noel Chiappa]

    > From: "Rob Jarratt" 

    > I did plug the connector back in, so that DCLO and
    > LTC are connected, I just removed the ACLO pin.

Ah, OK, good. Pulling the pins from those Mate-n-Loc shells without the right
tool is tricky; glad you did it, because as Brent Hilpert pointed out, having
a working DCLO is important, to reset everything to a known state on power-on.

    > I didn't look for replacements last night. Is there a modern
    > equivalent?

Not that I know of. Even if you found something with the same pin-out,
supposedly DEC selected ones that were 'good enough'. I've never had an issue
with NOS ones that I bought from vendors, though.

    > I may have found a source of NOS.

Great; get several, they're a useful chip to have around; the QBUS uses them,
as well as the UNIBUS.

If the same place has DS8640's (the receiver), save on shipping (and ordering
delays) and get a couple of those too. I say that because depending on what
else you had plugged into the UNIBUS post ACLO failure, the -15V may have
damaged them too.

The M9312 (not sure if you had one of those, but the -11/24 manual says it's
common in them) uses ACLO (via a DS8640). The KY24 seems not to (as far as I
can tell from a quick look - negative results from a quick print scan aren't
100.00% reliable, whereas positive ones are), oddly enough. In EUB memory
(not sure which you have), the MS11-L and MS11M MS11-P don't seem to, whereas
the MS11-P _drives_ ACLO (through an 8881) - probably to prevent CPU startup
until the ECC is cleared). Etc, etc.

    > I always marvel at how neatly those wires are done, I wish I knew how
    > to do such a neat job.

The same way the old joke says one gets to Carnegie Hall, I expect! :-)

(I wonder what the UK equivalent of the Carnegie is - the Royal Albert,
probably?)

	Noel