Re: //c RAM problems

[oaaland@aol.com (O Aaland)]

>Subject: //c RAM problems
>Vincent Quinn writes:

>Out of my four //c motherboards, three have problems :-(

>The first one has a bad IWM, so I'm prepared to sacrifice it to repair the
>other two

This is a good use of an early MAC, Up at least through the MAC PLUS the IWM
chip is the same as is used in the //c and on the UniDisk 3.5 card.


> both of which have bad auxiliary RAM. But can anyone help me
>identify exactly which chips on the boards need to be replaced?
>Board one is a ROM 0. It appears OK but the 80-column display throws a few
>rogue characters ($s and 0s) up on the screen. The self-test returns the
>following message:

>*RAM 0 0 0 0 0 1 0 0

>Running diagnostic programs on it gives the following:

>Auxiliary memory needs repair:
>Error 04 at 010B64

>Finally, FASTCOPY.SYSTEM gives another confirmation: "A memory failure has
>occurred...The failure occurred in auxiliary RAM".

>Board two is a ROM 255. The 80-column display gives real gibberish - many
>of the characters are displaying as something else (no, it's not because
>the Dvorak switch is down). Of course, there is no self test; but running
>the same diagnostic as above gives me:

>Auxiliary memory needs repair:
>Error 08 at 010800

>Is there anything else I can do to narrow it down? Also, am I right in my
>assumption that the chips marked MRD0-MRD7 are the main 64K of RAM and
>those marked ARD0-ARD7 are the auxiliary 64K?

Starting from the right front corner of the mother board the memory chips
run toward the back along the right side.

Starting from the back auxially memory is to the rear, front 8 chips are
main memory

Position               Error code
ARD7                    80 at xxxxxx
ARD6                    40 at xxxxxx
ARD5                    20 at xxxxxx
ARD4                    10 at xxxxxx
ARD3                     08 at xxxxxx
ARD2                     04 at xxxxxx
ARD1                     02 at xxxxxx
ARD0                     01 at xxxxxx

MRD7                    80 at xxxxxx
MRD6                    40 at xxxxxx
MRD5                    20 at xxxxxx
MRD4                    10 at xxxxxx
MRD3                     08 at xxxxxx
MRD2                     04 at xxxxxx
MRD1                     02 at xxxxxx
MRD0                     01 at xxxxxx


The xxxxxx would tell you the particular part of the chip that failed
but for what you want you can ignor that part (unless you plan to repair
the individual chip :) ).

It will be a lot easier just to get replacement chips since the ones in 
your //c's are all soldered in. It should be no problem to find used ones 
because they were used extensively in early PCs.

Owen Aaland