Thanks for the feedback. I am using a standard IBM
monochrome monitor.
I tested the monitor with another known-working card, and I also tried
another monitor. The problem is with the display card.
This is one of the original black connector versions of the IBM 1904057
I wasn;t aware there were several versions. What are the _real_ differences?
XM 407 display cards. It has 9114 RAMs in it, not
socketed of course,
so I think if I can probe each RAM chip first to ID the bad chip it'd be
more efficient. I would similarly have to check the 74L chips. oy!
I don;t think there are any 74Lxxx parts on that board, if there are, be
careful. A number of 74Lxxx chips ahave different pinouts ot the
74xxx/74LSxxxx versions, as people who work on HP9800s will discover :-)
I think I'd run a logic probe on the address pins of the RAMs. All should
be changing (due to the scan counters in teh 6845). If any are stuck,
then either a RAM has an internal shrt, or there's a problem wit hte
address multiplexer or the 6845 itself.
-tony