Question for the Bally MCR-2 guru's

yaryar

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Been working my way through some MCR-2 CPU boards lately, and I've got one now that has me stumped. Here are the details:
When powered on, screen goes to a pattern of horizontal dark green lines, and the screen stays locked up there. The problem is related to the CPU board, as video and SSIO boards were moved to another stack and test fine there. All socketed chips have been tested good in another CPU board. Voltages are all fine.
The CPU reset line stays high, so it isn't watchdogging. However, if you remove one of the ROMs and boot the board up, the watchdog will bark repeatedly.
There is no activity on A9 through A14 address lines, but with the oscope probe on say, A13, and pressing the reset button a few times, the exact same pattern of pulses will appear for a split second, then that address line goes low. It would appear that the program tries to run, but then 'locks up', as evident by those address lines having activity, then going low.
The INT line for the CPU on a working board is high with a regular low pulse. On the bad board this line stays pegged high all of the time, so it would at least appear something on this line is causing my issue. This signal comes from the Z-80 CTC IC. As mentioned before, I swapped all socketed chips so the CTC is known good.
The CTC gets its enable from the custom PAL at location E4. This custom chip has been swapped with a known good IC and no change.
So to the MCR guru's out there, what in the heck am I missing here?? Or am I going about this one the wrong way altogether by pursuing this INT signal?? Thanks in advance for any advice!!
 
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