IIGS CPU: Failed its self-test; what next?

[sebugg@presby.edu (Stephen Buggie)]

                  IIGS CPU FAILED ITS SELF-TEST AND WON'T BOOT;
                  ------------------WHAT NEXT?----------------


       I bought a non-working IIGS CPU unit for almost nothing ($15 plus
shipping), with the idea of cannibalizing parts like the power supply and
the external casing.  Now that it has arrived, I am awed by its showroom-
like physical condition ---- not a scratch or mark on it.  Internally, there
is no hint of any damage.  Impressed by its fine condition, I want to make
it a runner again.

       Problem is that it does not boot.  You get the checkeboard pattern
of characters in normal and flashing inverse.

       FAILED SELF-TEST:  I activated the internal self-test (both Apple
keys held down at power-up).  It goes through the early phases of the self-
test; then, when it gets to the flashing characters, it does not proceed
any further.  The sound test (ascending tones) happens, but SYSTEM GOOD
_fails to appear_.   Thus, there is a fault in the motherboard.

       BTW, the testing was done with no interface cards plugged in,
so don't blame the performance on interface cards.  I used a IIC monitor
while doing the test.

       Only three of the ICs are socketed: the CPU, a ROM chip beside it,
and a large long IC near the keyboard end.   I removed each of the three
socketed ICs; no change.

WHAT SHOULD I CHECK NEXT?  Could it be a bad 65c816 chip, or one of the
other two socketed ICs?  How risky would it be to a good IC to try
swapping with ICs from a perfect IIgs?

BTW, the keyboard and 3.5" Apple drive that came with it (extra cost)
appear to be o.k., so it appears the peripherals were not dragged down
with it.

Stephen      sebugg@presby.edu





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 ** Stephen Buggie  Psych Dept  Presbyterian College   Clinton SC 29325 **
 ** sebugg@presby.edu                 voice: (803) 833-8337 or 833-1632 **
 **             The Apple ][ pledge:  never to mess with MS-DOS         **
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