The Matrix

Maybe someone can show me the light here. I jsut cant seem to get my head around
this problem...

I have a Star Wars Main board which is passing all Matrix tests except A and C. For
A it returns 0001 and for C it returns 196A. Looking at the trouble shooting guide,
for the tests, here's what I know:

----
A. Accumulator Test
If the Accumulator Test fails, but Hardware Diagnostic Test 15 through 20 are
satisfactory, the problem is likely to be with the shift registers at locations 9A
and 9B, or the quad serial adder/subtractor at location 8B (all on the Main PCB).
Clears the accumulator.
Performs ACC= 0000 + (0001-0000) x 4000 (the result is 0001).
Stores ACC into memory.
Loads ACC back into register A and performs ACC = 0001 + (0001-0000) x 4000 (the
result is 0002).
Repeats parts 3 and 4 which results in the number in the accumulator doubling each
time. The sequence is 0001,0002,0004,0008,0010,0020,0040,0080,0100, 0200, 0400,
0800, 1000, 2000, 4000, 8000. (This is referred to as a "walking ones" test.)
------
So, the Accumulator isn't returning the proper # or is the register messed up? Also,
on test c:
------
C. Accumulator Adder Test
This test checks for a particular bit stream through the accumulator at location 8B
on the Main PCB as follows:
Clears the accumulator.
Performs ACC = (lB2C-0000) x 4000 + (196A-0000) x 4000 (the result is 3496).
------
It's not performing the first math.. But, subtraction is working fine (Tes d):
----------
D. Subtractor Test
This test checks for a particular bit stream through the serial subtracter at
location 8B on the Main PCB as follows:
Clears the accumulator.
Performs ACC = (2696-lB2C) x 4000 (the result is 0B6A).
---------------
So I've replaced 8B, 9A, and 9B.. No luck..
Any ideas? All are welcome.
Thanks,
JB
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