Ok, heres one I haven't seen before - a WPC-89 CPU that isn't willing to boot and displays continuously lit D21 (5v, ok) AND continuously lit D20 (Diag). Blanking D19 NEVER comes on. The board has been hacked around that area (u5, u21) but I measured continuity from the IC's and, while not looking pretty, continuity seems to be good. Also measured continuity on data lines A0-A15, D0-D7. Also tried multiple known-working game roms. Also tried different 68b09 and ASIC.

Lacking a logic probe, is there anything I can do at that stage? I didn't really find anything documented at for that condidtion.

Cheers,
Georg

Yep, forgot to mention - CPU is already isolated with only the power connector being connected.

Bump. Any ideas welcome.

Thanks for that - CPU jumpering is OK. I identified one more bad 74xx IC, U14 - but that didn't change anything.

Got myself an oscilloscope. The board shows no clock signal at U9 and U5. I'm also getting nothing on U9 Pin 37 (reset pin), which should be high but always stays low.

I suspect my next culprit is U10?

Cheers
Georg

Bump!

ok, I ordered a bunch of these. cheers