23 Nov
1999
23 Nov
'99
8:47 a.m.
> I had the following results when depositing 7777
to the memory.
>
> Memory locations: xxx0 - xxx3 don't save anything
> Memory locations: xxx4 - xxx7 save 7760
My guess is that eitehr E46 is faulty, or it's
never being enabled. The
enable is applied to input D of the chip (pin 2) , from the gates in E34
(74H10). This is not going to be hard to trace out.
Found the chip, and assume I should test it with a Logic Probe and Pulser,
with the data in the back I think I might be able to figure that out. One
question, in looking through the pathetic little manual with the logic
probe and pulser I have (not even sure why I have them, I've had it since
the late 80's and never used them), it looks like the board needs to be in
the system and powered up, as they get their power from the circuit.
to the entire card. You might look at E24 (8881) and
E28 (384). These
chips are quad line drivers and receivers and it's possible for an entire
I'm guessing the next step is to also take the logic probe to these, but I
don't find any data on these chips...
Do you know if the CPU board is correctly handling data
on the bottom 4
lines? Since everything is open-collector, it's safe to try grounding (to
the system 0V rail) the MD lines during a read cycle to see if the CPU
sees them as asserted (everything is active low). And to monitor them
during a write cycle to see if the CPU can pull them low.
Was hoping to look into this, but it took so long to figure out the
O-scope, that I'm out of time today, gotta be at work in 15.
Unfortunatly the next couple days are going to be busy so not sure how much
time I'll have to work on this until Friday.
Zane
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