16 May 2018

Xexex - Konami 1991 (repair log)

PCB was in very good condition but threw a "SOUND MEMORY BAD" error on boot up:


Of course this error isn't in the manual and even after an extensive online search I haven't found any mention of it anywhere...
Well after some probing and testing I came to the conclusion it had nothing to do with the RAM chips on the mainboard. I mistakenly thought it was caused by a bad '054539' custom chip (samples player) so bought a replacement pulled from an other game from Caius @ jammarcade.


I pulled the suspected faulty chip and cleaned the pads:


Then I aligned the replacement chip and soldered the 4 corners:


Then applied some SMD soldering paste:


And used hot air for soldering:


Only to discover it didn't change anything regarding behaviour of the board, still stuck on the same error.
So I had a look in the code and found this error is reported when the RAM present on the custom sound module is bad. Many of you know there isn't any RAM on this module but instead there's a '054321' custom chip handling, amongst other things, sound volume. I came to the conclusion the chip embed some RAM, which makes sense.
I swapped the sound module with a working one and indeed fault followed the suspected faulty one. I went even a step further and swapped the '054321' custom chips between modules: and boom we've got a culprit, the '054321' was obviously faulty.




Game fixed in a sense (although I don't have any spare '054321', at least fault is identified, it's just a matter of soldering a good chip now).

I then had an other discussion with Caius who told me he encountered similar symptoms on a Bucky'O Hare board few days later:


Damn it... I should have waited few more days before starting this repair.



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