That would cause backplane pins 2, 20, 22, 26, 36 to short together from one cable, and pins 38, 56, 58, 62, 72 to short together from the other cable.
I've done a little poking at the backplane about a year ago, and was able to take some reasonable guesses at some of the signals by direct measurements and looking at a broken 16531A scope module. The 16531A is thru-hole, so it was a lot easier to see where various traces were going.
Here's what I have so far. Any pin where I didn't have a good guess is not listed. I would think shorting the -5.2V supply did the most damage, since it's also responsible for supplying the power-hungry ECL on the modules.
Thank you both. I will eventually make an attempt to fix the shorted 16754A. But first, Ill take a stab at my three other 16754A boards that all fail the RC comp and Tap delay calibration. I have one good 16754A board that I want to compare with live on the bench.
So here's a summary of your information:
Pin(s) Signal
------ -----------------------
1-5 +5V
6-8 +3.3V
9-10 +12V
11-12 -12V
13-14 GND
15 D7 bi-directional (D7:D0 based on 16531A DAC)
16 D6 bi-directional
17 D5 bi-directional
18 D4 bi-directional
19 D3 bi-directional
20 D2 bi-directional
<= shorted to +5V (pin 2)21 D1 bi-directional
22 D0 bi-directional
<= shorted to +5V (pin 2)23-24 GND
26 from backplane
<= shorted to +5V (pin 2)27 from backplane
28 from backplane, A1 on DAC
29 from backplane, A0 on DAC
30 from backplane, 138 both decode select C
31 from backplane, 138 both decode select B
32 from backplane, 138 both decode select A
33-34 GND
35 from backplane, R/nW, select which 138 decoder
36 UNKNOWN
<= shorted to +5V (pin 2)37 from backplane, 134 both G2A not enable
38 UNKNOWN
<= shorted to -5.2V (pin 72)43-44 GND
53-54 GND
55 100MHz system clock
56 100MHz system not clock
<= shorted to -5.2V (pin 72)58 UNKNOWN
<= shorted to -5.2V (pin 72)62 from backplane, 138 decode G1
<= shorted to -5.2V (pin 72)63-67 -3.3V
68-72 -5.2V
I also found another two 16754A boards sitting in a stored away 16702A so I will need to fix the rail corrosion on those too.
This will all take a lot of time...
Thanks,
/John.