Symptom: No RGB output
Cure: Traced the Red signal back to pin 6 on an LS32 (IC57) on video board, it was dead. socketed and replaced the IC and everything is back
Note: This was a (Super) Bobble Bobble bootleg board but I think the majority of the layout etc is the same
This game was completely DOA. Checked the clock signal, all fine. Checked /RESET line of Z80, stuck low.
I replaced resistor R30 (330ohm) which is part of the Z80 reset circuit, it fell in half on removal.
The /RESET was now HIGH but all the address line were stuck.
I pulled both the Main and Sub Z80’s, both failed tests.
Also found 2 dead EPROMs. Burned 2 x 27256 eproms( a78-07 and a78-08)
All seemed to be firing up after that.