7 Nov 2018

Raiden II 'new' - Seibu 1996 (repair log)

This is the 'new' version of the game with audio of lesser quality amongst other differences.
Board was really clean, no visible damage or severed trace. However graphics were heavily corrupted (sorry for the pictures quality):

Some sprites were filled with garbage and background was messed up too.
Unfortunately this game doesn't have any kind of diagnostic menu and components being SMD it wasn't possible to do piggybacking. Also most of the chips were customs... In other words problem could be caused by either RAM chips and in this cause could be repaired, or the custom chips and the board would end up in the scrap pile.

I quickly identified the many RAM chips used:
- U021/U022/U027/U028: work RAM
- U0726/U0727/U0728: sprite RAM
- U0527: background gfx
- U0528 : texts
- U0824/U0825: colour RAM

By probing sprite RAMs I found U0726 had weak data signals: replacing it fixed the sprite issue.
Then background problem: again replacing U0527 fixed it:

As I didn't have any 6264 type RAM in my stock I used 62256s, they are 4 times bigger (32kb instead of 8k) but share the same pinout appart from pin 1 (NC on 6264, A14 on 62256) and pin 26 (CE2 on 6264, A13 on 62256):

Here's a simple trick I use in this case, pin 26 isn't a problem as CE2 must be connected for the 6264 chip to work, however, pin 1 being not used it's not rare it's simply not connected to anything on the PCB, and this was the case here. When using a 62256 instead of a 6264 some run a wire from pin 1 to Vcc or ground, but I prefer to simply bridge pin 1 & 2 together, RAM chips being simple one dimension arrays, as long as you read data back at the same place where you wrote them it's fine:

Game fixed.

P.S.: On last hint, the Raiden II "new" and Raiden DX "new" boards are identical and in fact 2-in-1 boards. To swap game, on boot up maintain player 1 controls as follow:
- all 4 directions (needs a joystick hack) + button 1 to swap to Raiden II "new"
- all 4 directions (needs a joystick hack) + button 2 to swap to Raiden DX "new"
Also please note swapping game erases settings.

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