IIc ramp chips mapped from self-test

[sebugg@presby.edu (Stephen Buggie)]

I do not know why our college's recently modernized "Pico" e-mail
editor deleted my message, but here it is (hopefully) again....

sebugg@@presby.edu                                        Dec 22, 1993

                   IIC RAM CHIPS: MAPPING FROM SELF-TEST



Today I sucessfully replaced the burned RAM chip which was soldered to the
motherboard of my unidisk IIc.  This was the second RAM chip to blow on that
board.

Last week I asked the Apple group to help me interpret this error message
on the self-test:

            RAM     0  0  1  0  0  0  0  0

I could not find the explanation in the IIc Tech Ref manual, which I have.
Four persons responded by e-mail, and all agreed that the bad chip was one of
the eight chips in the MAIN MEMORY bank;  addresses of the eight chips in the
other (auxilary) bank are preceded by an asterist, *.  But my advisors
disagreed
whether the counting within the main bank was FROM the keyboard end, or
instead
TOWARDS the keyboard end.  Also, the numbering within each bank begins with
chip zero, not with chip one.

What follows will be a complete chip-by-chip pairing of the self-test
error codes and the location of each chip.  Perhaps this could be added to
the FAQ Frequently Asked Questions since the information is not presented
clearly anywhere else.

Of course, this information applies only to the middle model of IIc computer:
the "Unidisk IIc."  The older"original IIc" lacked the self-test;  the newest
model, the platinum colored "memory expansion IIc" used only four memory
chips, not 16 as in the original and unidisk versions.

I would recommend strongly that users of the oldest "original IIc" should
take advantage of the free motherboard upgrade.  The upgraded board has the
diagnostic self-test;  without the self-test, I would have had no clue
as to which of the 16 chips was bad!

I installed a socket for the replaced chip (location MRD5), so that if the
RAM chip blows again, I will plug a new one into the socket.  About 12 of
the 16 rams can be fitted with sockets;  the remaining four rest neat the
edges of the internal disk drive, so sockets would make the chips too tall
in those locations.

=============================================================================
    UNIDISK IIC SELF-TEST ERROR CODES                    4264 RAM CHIP
                                                   (labeled on motherboard)

      RAM     0  0  0  0  0  0  0  1                   MRD0

      RAM     0  0  0  0  0  0  1  0                   MRD1

      RAM     0  0  0  0  0  1  0  0                   MRD2

      RAM     0  0  0  0  1  0  0  0                   MRD3

      RAM     0  0  0  1  0  0  0  0                   MRD4

      RAM     0  0  1  0  0  0  0  0                   MRD5  (I REPLACED IT.)

      RAM     0  1  0  0  0  0  0  0                   MRD6

      RAM     1  0  0  0  0  0  0  0                   MRD7



    * RAM     0  0  0  0  0  0  0  1                   ARD0

    * RAM     0  0  0  0  0  0  1  0                   ARD1

    * RAM     0  0  0  0  0  1  0  0                   ARD2

    * RAM     0  0  0  0  1  0  0  0                   ARD3

    * RAM     0  0  0  1  0  0  0  0                   ARD4

    * RAM     0  0  1  0  0  0  0  0                   ARD5

    * RAM     0  1  0  0  0  0  0  0                   ARD6

    * RAM     1  0  0  0  0  0  0  0                   ARD7

=====================================================================

I suggest that this information be added to the FAQ file; the IIc is
more likely than other models to burn out RAM chips because of its lack
of ventilation within the casing.


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