The never ending repair thread!!!
Every now again this board comes down from the shelf for further investigation and repair attempts. I've since had success with other boards but this PCB is my Nemesis!
After watching a repair video of Hammy's stating that the mask ROMS where 27C800's split in two with the same data in each half I de-soldered one of the graphics mask ROMs and attempted to read it. After I split the contents 2 x 512k banks into 4 x 256k banks and ran them through Romident it recognised them as Street Fighter 2 RK bootleg version.
I changed the sub-board ROM socket a while back into a turn pin so I could still keep trying the 4 x ROM sub board but also throw a 27c800 in the socket. I noticed a board for sale on Worthpoint a while back and someone else earlier linked to this image which is my board with a single main CPU ROM! (see pics last one is mine).
Anyway I've put the main CPU ROMs from the RK version on a 27C800 and I'm getting address and data line activity again and occasionally music but I'm not sure I've burned them in the correct order it's a bit of a faff with an adapter and bank switching.
Anyway and this is the real kicker!!! Before all this when I was checking other stuff on the board I slipped with the logic probe and shorted a 74LS157's under the graphics prom chip. The screen went blank and hasn't come back since so I'm working blind at the moment. No Sync at the edge connector and no activity on RGB lines. I've checked the 16hz crystal and that's good and I can pick it up on pins 1 and 2 of of PLD U151 but from there no further. I traced the sync line back from the edge connector to pin 21 of U131 but it has no activity at all at that point.
Any tips to get some graphic output back gratefully received...
I'm assuming probably incorrectly that the row of PLDs running horizontally through the board U151, U125, U96, U95 are graphics related and I may have wiped one of those out?
At this point it's been put back on the shelf.
