More Omega Race notes

Working on my second boardset now. Started by fixing acid damaged
areas, then plugged in the fluke 9010a.

I worked a fair bit to finally get it to read the ROMS, and then the RAM
SHORT on the 2 sets of ram (4000-4BFF and 8000 to 8FFF).

Once I got those to work ( and ram short did find a problem with the
third test, an address line was not working).

I then figured I was on to the vector generator. I had a bad looking
output from x and y, top left only, small trapaziod.

Spent a fair amount of time tracing back to bad opcodes, and eventually
I figured the vector RAM was not getting the proper information. Looked
all over the place, then noticed I was resetting every 2 seconds. D'oh.

I went back to the 9010a and ram short was still working fine, so I
tried RAM long on the cpu mem (4000-4BFF), all is well.

Tried RAM LONG on 8000 to 8FFF, and the fourth algorithm failed. Some
pattern thing.
To isolate it as a RAM chip, or an addressing issue, I tried RAM LONG on

8000-83FF - Fail Wrote FF read FE
8400-87FF - PASS
8800-8BFF - PASS
8C00-8FFF - PASS

Looks Like I have a problem with one chip. Used the manual's self test
screen capture to figure where the chip was, swapped it.

So I think I am now on to problems in the vector generator.

One neat thing, for looking at the self test results on the bench, I too
an old connector from a williams machnine, which has the punch down wire
conections, and punched down an LED and put it on the header for the
sound board, now I can see the self test flashing the start LED's for
diagnostics.

Mike

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Received on Fri Nov 14 09:50:17 2008