Tempest FROZEN, passes self test

This message was posted in RGVAC, and I haven't had a SINGLE reply yet!
(over those yahoos heads I guess). I was told all the smart people left
and are on this list, so here goes folks.

I'm fixing another Tempest boardset (4th and final). I have several
boardsets available, so I know everything but the main board is good.

This boardset passes the self test (no bad RAM beeps, no error codes), but
when switched to normal play mode, it freezes up (no X or Y board output
(flatline on scope), solid player select LEDs). I've swapped CPU's with a
known good one, and swapped ROMs with a known good set. I've tried various
dipswitch settings (started with factory, then to free play, etc.), so I
know it's not the dipswitches themselves or their settings. I've also
swapped the aux board with a known good one.

(Other *obvious* info: checked & verified voltages, clocks, dipswitches.
Other good boardsets work in the same cab).

I'm thinking the freeze mode is stuck active, but know nothing about it.
Any ideas, suggestions, or advice? Have scope, will fix. Thanks in advance!

--
John G. DeGroof
jdegroof@ix.netcom.com
http://pw1.netcom.com/~jdegroof/john.html