20 Mar 2019

Raiden - Seibu 1990 (repair log)

Got this board in a lot of faulty boards in a trade. It came in an antistatic bag with a note written on it "will not boot".
Upon first inspection I noticed board was very filthy so probably hadn't been stored in the bag all the time. Also custom chip UEC-52 was completely missing (ripped from the board). Fortunately Caius from jammarcade.net sells reproductions of it, only I placed an order for one few days ago for an other board which had the chip scratched to the point only legs of the SMD ICs mounted on it where left. At least I'll have the ICs reference from the reproduction.

I usually find very few information about what a board should do with missing elements, which is a pity since this can be extremely useful for repairs.
Here are few things I can tell:
- without the UEC-52 custom chip (DAC used for colours in SIL22 package) the game still boots and plays blind
- the board requires -5V for sound, this probably explains with the board was noted "will no boot" when it fact it did but played blind, only to notice it you need -5V
- sound part is completely independent so even with a completely dead main CPU or sub CPU you are still able to hear the coin jingle if the sound part is alive since it's an interrupt (jingle is played whenever you insert a coin, wherever you are in the game)
- without the OBJ1 daughterboard game still boots and plays blind (black screen)

So as said game wasn't completely dead but played blind due to the missing custom chip. Fortunately I had received an other Raiden board few weeks ago which was perfectly working (and turned out to be an undumped set).
Could it be as simple as installing back the custom chip to get a fully working game?

Not really, I did so and then found valid signals on the RGB outputs, which was progress, but sync, despite having activity, wasn't valid. I inspected the board again and found a severed trace on the part side. I patched it and that did the trick:

Game fixed.

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