16 Nov
2003
16 Nov
'03
11:12 a.m.
From: "O. Sharp" <ohh(a)drizzle.com>
I fear you are right. I had thought there would be *someone* who knew,
remembered something, or could look it up.
Does the lack of replies really mean no-one knows
what an M750 "Line I/O
Control" is for?
Sticking my neck out a bit, I thinks that may be a "yes". :) A part of me is beginning to wonder if they're
even -8 related, or if
they just happened to be with the stuff you got. If I had DEC Logic
Handbooks for years _other_ than 1969, and for products _other_ than
the -8 series, I'd try looking them up elsewhere - maybe they're
related to the PDP-10s, -9s, -15s or somesuch. Is there someone with
a better DEC library who can take a look?...
I had that thought also. I have some logic handbooks, and have Googled like
mad, but no luck. I did manage to largely exhaust the possibilities related
to PDP-8/i peripherals and options, so it is starting to look likely that
they have nothing to do with the 8i they came with.
Do they have ICs on them, or transistors and diodes
and whatnot? That
might be a way to narrow down the dating. (I don't suppose by some
miracle any of them have a manufacturing year marked?...)
I put a description of them on alt.sys.pdp8 some time back. I'll attach it
at the end of this message.
> Does that also mean no-one wants any :-)? I have
pretty much decided
that
whatever they
are, I am not likely to need them.
<smirk!> Oh, I'm sure we _all_ want them. God knows what for, but
they must be useful for _some_thing. :) :)
-O.-
<listening for the inevitable demand for M750s about
eight or ten years from now, with eBay prices reaching
about $6,000 a board... <g!>> How about some clues. What does an M750 look like?
Size (width),
major chip content, connectors? This might help ring a bell in
someone's mind.
OK, I pulled a couple out of storage to look at. The form factor is
your standard single-wide flip-chip stuff that the 8i and 8L are made
of. There are four transistors near the purple handle, with four
resistors in the center separating them into two pairs. Then there is
a row of four TTL chips; 7440, 7474, 7402, 7474 from left to right.
Next is a row of 2; a 7402 and a 7400. Next is a row of diodes and
resistors. Lastly, two more TTL chips, a 7400 and another 7402. Each
TTL chip has the standard .01 bypass cap, and there are assorted
resistors and diodes here and there, too, There are three small
electrolytics, one on each edge of the row with the diode and resistor
grouping, and another on the right edge of the second row of TTL.
Both side 1 and side 2 of the edge connector are extensively used, as
opposed to the simpler cards where only side 2 has fingers.
The one that is marked M750A has a cut trace going to what I think is
N2. The M750B is missing that trace, but has an oversize finger
there, as if someone thought they might need to solder to it. On the
other hand, the M750A has an oversize finger at what I think is R1,
but on the M750B there is a trace there that seems to go to one of the
7402s. The rest of the component layout, resister values, etc.
between the two versions is virtually identical.
Hope that helps!
Vince