Re: Omega Race CPU repair

That's a good point John. Disconnecting the monitor. I really should be using two
scopes to do this board. One for probing, and the second hooked to the X and Y
outputs without the monitor attached. The steps you have are good ones:

1. Verify ROM checksums.
2. Replace any corroded sockets/chips in battery area.
3. Verify RAM viability (in another game, or replace with known good).
4. Verify fuse sizing and operation.
5. Set game to test mode.
6. Disconnect the monitor.
7. Power up, and check voltage regulator output levels.
8. Check pin26 for CPU Reset (WDOG problems)
9. Trace back the '74 '00 '08 '138 chips for operation (used in generating WDOG)
10. Ensure CS is getting to the ROM's.

And that's kind of where I stop. Your idea of checking discontinuous traces near the
battery makes some sense. I'll check that area. And if Al gets too overloaded with
work to get the scan's up, I'll take you up on the copies!

John Robertson wrote:

> I can sell you a good photocopy of the schematics, as for the WDOG, you
> can disable it for testing purposes, I NEVER have the monitor hooked up
> until the scope shows good signals on both X & Y axis. Put game board in
> TEST so a crosshatch would be visible, then check the outputs. Also this
> game has a lot of problems with battery corrosion, you need to replace
> any IC sockets that have any sign of the alkaline reaching them, also
> traces can be etched away, a continuity test of these would be good
> around the battery area.
>
> I assume the board voltages are all good and were measured on the game
> board...
Received on Wed Jun 9 11:07:53 1999