Finally got to poke around some more, I'll break down your post with the systematic checks through the signal chain. Readings that were at odds with your references are in bold. Stop, Play, rec button down, rec
Using your scope on the analog motherboard look for the 120 KHz erase signal on J9 pin 1 (erase hi). (in all 4 modes I expect: 0,0,signal,signal) This will show us it the erase signal is making it out of the analog motherboard (after passing through the record relay)
I get 0, 0, signal,
almost no signal
Next is to look for the 120 KHz signal at J7 pin 10. (expecting: 0,0,signal,signal)
I see 0, 0, signal,
smaller signal
Next is to look for the 120 KHz signal at IC2 pin 6 and IC2 pin 2 on the bias board. (expecting: 0,0,signal,signal).
IC2 pins 2 and 6 both: 0, 0, signal,
0
Next is to look for a voltage on the bias board IC1 pin 14 (expecting: 6.78,6.78,1.99,1.99)
6.8v, 6.8v, 2v,
6.8v
Next looking for the voltages on P7 pin1 (expecting: 0,0,22,22)
0, 0, 20.3,
0
Question - Does the record lamp come on in rec hold and stay on in record?
Yes it does. The lamp goes out when the button is pressed down, but when released it stays lit in record.
On the audio motherboard look at J10 pin 1 (expecting: 0,0,22,22)
on the audio motherboard look at J10 pin 2 (expecting: 0,0,22,0)
J10 pin1: 0, 0, 21,
0
J10 pin2: 0, 0, 20,
19
Verify that rec hold (J10 p1) and rec (j10 p2) are the same as above on the strip board power supply connection pins 6 and 3 respectivly.
Yes, they're the same as above (both incorrect compared to yours with rec button released)
Verify that these signal are the same in the power supply J88 [sic] pins 10 ans 13. THis connector is not otherwise listed in my schematics. I presume that it goes to the transport motherboard one way or another. And Rec hold is fed from J33 pin 10 and rec from J33 pin 9
I couldn't get to J86 to get that measurement...however, I did check at interface/lamp board J38 pins 1 (rec mom relay driver) and 3 (rec hold relay driver) and got the same as above for J10, that is to say rec mom is 0,0,20,
0 and rec hold is 0,0,20,
19, so J86 should measure the same.
Check transport motherboard J33 pin 10 (expect: 00,5,0)
Check transport motherboard J33 pin 9 (expect: 0,0,5,5)
J33 pin10: 0,0,5,0 same as yours!
J33 pin 9: 0,0,5,5 same as yours!
I think I lost my way at this point - there is plenty to look at there. I'm just going to have to trace out the signal path in my deck tonight.
There's not a whole lot left to look at after that; moving back through the logic board from J33 pin 9 ("record out") goes to pin 3 on our old friend Record IC6.
From J33 pin 10 (mom rec), it goes through Edit IC7 then Record IC6, so I suppose there are some more pins to test!
Also, I did swap in a new replacement for Record IC6 and no change (I suppose we expected that).
Should I be suspicious of the transistors in the path through the interface/lamp driver board?
THere are errors that I have found on my schematics. I've been popping back and forth between some 110a and 110b schematics as that the copies I have (pdf) are none too clear.
I can do some cleaner scans of 110c schematics; drop me a pm if you need any.
Turns out I had been probing the wrong pins when I quoted the goings on with IC6p13 and IC5p8...didn't realize until I pulled the card today and took at look between the two...sorry...I'm still learning! 
