RESOLVED: SEGA "Y Board" aka SuperScaler system. (G-Loc 1991)

[ArcadeMachinist]

I had this board working about a year ago.
Tried to run it yesterday and it would not boot.

MAME for ref: https://github.com/mamedev/mame/blob/master/src/mame/sega/segaybd.cpp

I looks like First MC68k CPU IC12 (315-5314 on MAME ascii art schematic), is stuck in a boot loop, 2 other MC68ks are idle (not booting).
CPU resets about 3 times per sec.
* RST pin jumping up/down 3 times per sec (50ms low/300ms high)
* 12.5 Mhz clock signal is ok
* Activity on address and data buses.
* Voltage levels are ok (4.89V should be ok)
* CPU2 & CPU3 RST stays low (I guess CPU1 would init that, farther during the boot)
* there is a clean video sync signal (video is a separate PCB under the main one)

I suppose some UV erasable roms went bad? sram?
Any reccomendations on approach to diagnostics?

There is just 1 electrolytic cap around, there is clean VCC around it, so it should be fine.

 

[ArcadeMachinist]

Update: CASE CLOSED

Upon further investigating address and data lines with my scope I found out that one of the data lines behaves weird on SRAM chip pin.
Doing some extra measurements it seems like there is a trace damage between EPROM socket and SRAM pin.
However that trace is completly covered by the SRAM chip itself, so turns out to be some corrosion under it?


Jumped the trace on the backside of the board. Works.