29 Jun
2007
29 Jun
'07
8:28 p.m.
Can someone
help me understand these old HP schematics?
I see the 15 adapter pins shown at the top right of the
page, and see where one of the pins (# 5) appears to go
to something labeled EIA IN on the "Logic Mother Board"
FWIW, 'EIA' was commonly used at that time (particularly by HP) to mean
what we'd normally call 'RS232;
section. Some pins (3, 4, and 6) appear to not
be
connected to anything. Most of the others seem to go
to the Analog Mother Board, but I am not sure how to
follow them from there. What would be nice is if I
Given the one sheet of schemaatic that I've seen, you can't. You need
detailed schematics of the motherboards to trace the signals to pins on
the plugin cards (I assuem) and then scheamtics of the approprtiate cards
to see where they go in the 'real' electronics.
Do you have that information? 
29 Jun
29 Jun
2:25 p.m.
I have spent a little more time looking at the information that I
have. My documentation does not include detailed board schematics.
That, alas, is what I half-suspected. Some HP manuals contain very
detailed scheamtics, others don't (and there seems to be no 'pattern' to
which will and which won't).
I'd like to help you, but unfortunately at the moment I am 'working
blind'. I don't have such a plotter, and I don't have the manuals. I
suspect if I had the insturment in front of me, I'd spot a lot of things
quiote quickly.
However, these boards do not look extremely complex.
I have figured out
how the pins on the interface are numbered. The top left pin is #1 and
the second (lower) row contains pins 9 thru 15 (left to right). I have
Isn't this just a standard DA15 connector?
followed these wires from the adapter to the board,
where they are
connected. At the point of connection, there is a number like 901, 902,
905, etc.
I'll bet those identify the wire colours, as I described last night. 901
is white with black and brown strips, 905 is white with black and green
stripes, etc (think of the resistor colour code, if you don't know it,
find it ;-))
I also found a page in another manual that shows how
to hook the
interface cable to an ASR-33. It has an "in-line" molex style adapter.
Do you actually have wirelists/schematics for the cables?
I need to look at that connector on the ASR33 and see
how many wires it
contains. Tony probably knows that answer off the top of his head.
Which ASR33? No, that's not a stupid question, there are many versions of
the electronics ('call control unit') used in the ASR33,. with many
different connectors. The most common one for computer/private line
working has a 9 terminal barrier strip, not a molex connector. Anyway,
manuals for the HP version of the ASR33 are on www.hpmuseum.net
How I'd tackle this (but rememebr I've done this before ;-))
FInd a logic ground inmside the plotter, determine if any of the DA15
pins go there (I'll bet at least one does). Ditto for chassis ground.
Find the power rails, at least +5V, +12V, -12V. If necessary from power
pins of known ICs. Is there power brought out on the DA15? If so, it's
posssible some of the cables contained circuitry :-(
Look for RS232 drivers/receivers. This thing might use the traditional
1488/1489 chips (but they might be house-coded!). It may be old enough to
use a 1489 for receive and an op-amp as the transmit driver (HP certainly
did this in other devices). It may even use discrete transistors in part.
If you can identify these circuits, see which pins on the DA15 go to them
Look for the current loop circuit. The receiver is almost certainly
opto-isolated, and optoisolators are the only common 6 pin ICs. Is there
one. If so, trace out the circuity rounf the LED side (pins 1 and 2 of
the chip if it's conventional). That should go back the the DA15 too.
That's a start. If I had the unit in front of me, I'd probably spot quite
a bit in a few minutes....
-tony
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