Data East Night Slashers arcade pcb repair
The game booted to a pink screen with some garbage sprites visible. With this board and other Data East boards of the same era (Captain America, Locked n Loaded, etc) that’s a sign the CPU is running at least some of the program correctly. That’s because the CPU must enable the graphics output manually. So if that CPU hadn’t been running this board would just have booted to a solid black screen.
With the program ROM ok, next likely problem is the RAM, though it’s usually quite reliable on these boards. I had another idea the problem might be the security/input IC, marked 104. I used a custom build of MAME to fake a bad 104 chip, and behavior matched the real board – the program ran far enough to enable graphics, then just looped waiting for the security IC to respond.
The 104 chip is used on a handful of other Data East titles including Caveman Ninja, Pocket Gal Deluxe, Wizard Fire, Rohga, etc. I took a chance and desoldered a 104 from a Caveman Ninja, and success – the game booted!
Some tilemaps had bad colors – however this was easy to find – lifted pins on one of the ’56′ tilemap customs. After a reflow all the graphics were correct.
Still no sound – an obvious problem was corrosion on the program ROM and socket. A replacement ROM didn’t bring back sound but a logic probe now did show the ROM data lines appeared to be pulsing correctly, so the CPU was hopefully running. The main amplifier is usually the first thing to check for sound problems, and as I didn’t hear any background hum at all I suspected it was dead. This amplifier is actually quite easy to obtain new as it was used in many televisions, so a brand new one was ordered and fit and sound worked.