23 Nov
1999
23 Nov
'99
8:31 p.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.
Hmm, I'm almost safe with this thing, looks like it's a good thing that the
system appears to be fairly robust since it doesn't seem to be any more
messed up that it's been. Just realized I was testing the G227 board with
+15V hooked up to the Logic Probe, which explains why the probe was just
beeping, instead of showing the change from high to low and vice versa (of
course I realized this after swapping the G227 and G104).
However, it looks like E46 is indeed bad. It doesn't seem to function like
it should. On E39 some of the legs get a single blip every eight examines
(yes, I know that isn't a very good way of describing it, but I didn't take
notes, plus I wasn't using the probe right).
BTW, both E46 and E39 looked to be getting blips at the right spots on Pin 2.
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... For example. Put the logic probe on MD0 (MSB) on the
backplane and
deposit 7777. It blips low, right? Now examine that location (assumed to
be a 'working' location) -- it blips low again.
Now look at MD11 (LSB) and do the same things.
All 12 lines of the MD Bus look to be functioning both ways. This was
tested with the proper voltage hooked up to the probe.
Zane
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