Apple /// memory problem

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Joined: Feb 17 2013
Posts: 149

Anybody here know anything about throubleshooting the bank-switched memory on an Apple ///?

This machine was working perfectly until I tried upgrading the keyboard to a /// Plus keyboard-- this requires replacing the encoder ROM as well as the keyboard.

Simple enough, but the computer would not boot SOS afterwards. It displays the screen and then crashes. Memory diagnostic tests pass "bank 0" and then die.

I completely replaced all the memory chips (this is a 256K model) with NEC 4164s, and the symptoms did not change. I suspect the problem is in the circuitry that handles the bank switching, but I don't know what to try next. Any suggestions would be appreciated.

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Joined: Jul 31 2014
Posts: 34
Re: Apple /// memory problem

Hi,
There are some troubleshooting flow charts and info in chapter 13 of the A3 service manual, and on page 13.55 there is some memory specific information. This may give some clues or help.
Are you able to get into the monitor by pressing open-Apple control reset?

/Rob

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Joined: Feb 17 2013
Posts: 149
Re: Apple /// memory problem

Where would I find one of these service manuals? I don't see them on the Apple /// resources site...

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Joined: Oct 9 2013
Posts: 367
Re: Apple /// memory problem

dramsey wrote:

Where would I find one of these service manuals? I don't see them on the Apple /// resources site...

Not sure this is the exact document referenced but perhaps this will suffice: Apple /// Service Reference Manual

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Joined: Jul 31 2014
Posts: 34
Re: Apple /// memory problem

Yes, that is the one. sorry, I should have included a link in my original post. There is a lot of good information in there. Let us know how you get on.

/Rob