Yet more on -8/m Mem problems

From: Zane H. Healy <>
Date: Tue Nov 23 16:47:30 1999

>> 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 H. Healy | UNIX Systems Adminstrator |
| (primary) | Linux Enthusiast |
| (alternate) | Classic Computer Collector |
| Empire of the Petal Throne and Traveller Role Playing, |
| and Zane's Computer Museum. |
| |
Received on Tue Nov 23 1999 - 16:47:30 GMT

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