Atari pinball repair question

Hello all,
I'm trying to repair a Superman pinball by atari. I'm an electrical
engineer with some decent experience repairing stuff of this nature,
just not well versed in atari pinball. here's the lowdown;
1. The voltage regulator and big bypass cap were bad, replaced them and
the processor board powers up and the pin correctly goes into "attract"
mode (cool blinky lights). Coin lock solenoid doesn't close, and
displays (LED) don't work at all.
2. I can go into test mode with the button in the coin door, but it
gives me a flashing LED #3 and 4, so I bypass with the start, test
button combo and continue. I'm not sure what these LED's mean, but it
seems to indicate some sort of processor PCB problem
3. The LED displays don't work at all in the first test
4. in the coil test, every coil fires correctly (flippers and coin door
lockout included)
5. In the lamp test, all lamps and input switches work correctly. The
sounds seem to work as well.
6. all other test have to do with the LED displays, which don't power
on. they're all book-keeping related and don't matter at the moment
7. after cycling through test mode, the machine returns to attract mode

I'm guessing that RAM might be a culprit in this board, but I suppose
some ROM's could be bad as well. I have the 3 PROM version of the game
(not 6 EPROM). It looks like the correct voltages are getting where
they need to be, so I was hoping anyone out there could give me some
general information on what they think could be the problem. I can
provide specifics on my testing as the thread progresses, and thanks in
advance for any advice you can give
~Ryan Hunter

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