IIC self-test error message: RAM chip bad

[sebugg@presby.edu (Stephen Buggie)]

             WHICH IIC RAM CHIP IS BAD?  SELF-TEST ERROR MESSAGE
             ---------------------------------------------------

One of my IIc Apples is a middle vintage "Unidisk IIc."  Its RAM memory
is 128K of 16-pin chips which are in one continuous row along the right
edge of the motherboard, when facing the computer (viewer's right side).

While testing an external modem, I just got a RAM error.  In fact, it
seemed that the computer jumped right into the checkerboard-pattern
self-test display.   The error message that is staring at me right now is:

              RAM     0  0  1  0   0   0   0   0

The computer will not load programs --- it either goes into the asterisk
"monitor" display, or into the self-test, and the error message occurs
soon when the self-test occurs.

I know that this message tells me that one of the 16 RAM chips is bad;
with the same computer two years ago, I replaced one bad chip, which
fixed the problem.  It was a RAM error message at that time, but the "1"
was located elsewhere.

The advice I seek from the group is to IDENTIFY WHICH OF THE 16 RAM CHIPS
IS BAD AND NEEDS REPLACEMENT.   In other words, counting from the keyboard
front end to the back panel, which numbered RAM chip is the bad one?

Having successfully replaced a soldered motherboard chip with a socketed
one two years ago, and having all the parts (chip, socket, special solderer,
etc.) all on hand, I know that I can do it, but I want to be absolutely
sure which RAM chip is actually bad!

PLEASE ADVISE ME VIA E-MAIL:   sebugg@presby.edu

I prefer to get the advice directly so that each advisor is "blind" to
the opinions of others.  Then, if there is a consensus of opinion regarding
the identity of the bad RAM, I will feel confident that I will remove the
correct one!

After the repair is completed, I will make a brief follow-up report directly
to those who advise me and also to the A2 board in general.

BTW, I was told two years ago that, when one RAM chip fails, others are
likely to fail also.  I will install a socket again this time, if sufficient
headroom is available above the socket.

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 ** Stephen Buggie, 410 Chestnut St., Clinton SC 29325    Apple IIe/IIc **
 ** sebugg@presby.edu                 voice: (803) 833-8337 or 833-1632 **
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