16 Sep
2015
16 Sep
'15
11:23 a.m.
From: tony duell
Do you have a URL for the prints (to save me going
through all possible
candidates on bitsavers)?
Yeah, as per my 'where are subsystem prints' page, they are in the 11/23
print set MP00740, pg. 81-87 (schematic on pg. 87):
https://archive.org/details/bitsavers_decqbusMP0_10391074
(Doesn't seem to be on BitSavers?)
What is the fault with your board?
First, I should explain that I do have a working PM board, so we can swap back
and forth to see what a working one looks like. It also verifies that the
fault is on that board, since the working one is fine in that chassis.
Anyway, on the bad one, both ACLO and DCLO (BPOK and BDCOK, I guess the QBUS
guys call them :-) are being pulled low.
Looking at the board, D5 (the Q3 end) is at ground, the other end is at
around ~-3V; with D4, both ends are at ground. On the good board, both
ends of each diode go to -12V shortly after the machine powers on.
(Advance thanks for any help! :-)
Noel