17 Apr 2019

Ikari III: The Rescue - SNK 1989 (repair log)

Game got stuck on the memory test screen with palette error C4 and sprite error P15.
I pulled both RAMs (6116 type for the palette, 6264 type for sprites) but they both tested good out of circuit.
As you can't rely 100% on out of circuit tests I installed 2 fresh chips on sockets: errors were still present.
By probing the RAM chips them I could see some signals were floating: board had few points of corrosion and a couple of traces got severed.
I patched them all and then board booted into game but only the very top of the screen was visible:



I continued my inspection of the board, testing continuity of each dodgy point when I found pin 12 of the LS367 @D7 was floating.
For once schematics were available (quite unexpected since Ikari III is a bit of an uncommon game) and from them I learned missing signal was AB11 (address signal buffered through a LS244). Again I patched the severed trace and fault vanished:




Game fixed.

P.S.: This game seems to accept rotary controls through additional connectors on the board but is also totally playable with a joystick from JAMMA inputs.

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