RM02 Massbus adapter troubleshooting

[Patrick Finnegan]

I'm trying to get a few RM02 drives going, which I picked up about a 
month ago.  I can't get the RH11 I've got to talk to the MBA (Massbus 
adapter) in the drive (it reports a 'timeout'), and I think I've traced 
down the fault to a problem with the massbus transceiver, but wouldn't 
mind someone else taking a look at this...

On page 2 of the M5922 schematics, signal AA2 DEMAND A H is generated 
from a 75108.  It looks like the signals "IF5 PORT A ON H" and the 
global enable from the switch on the board are both high and "MASS FAIL 
H" is low (and thus "AA2 MASS FAIL A L" is high).  When the controller 
toggles the DEM(and) line on the massbus, I see "MASS DEM A H" 
and "MASS DEM A L" at pins BV2 and BV1, respectively, change state, but 
the output "AA2 DEMAND A H" stays low.

Any ideas?  I guess that either the 7417 at E3 could be defective, or 
the 75108 at E17 could be to blame.  Or, is there something else that 
I'm missing?

BTW, after staring at the MASS FAIL logic for a while, I looked up a 
datasheet for a 7417, and realized that it's just a buffer, and not an 
inverter (as it's drawn in the print set).

Pat
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