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Capcom CPS 2 B Board Repair Log


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Wife and kids were out, so I went to play some 1944 - The Loop Master (personally I like 19XX a lot more!).

Near the end of the game the system crashed and displayed that "Error Exception Handling" black screen. So I turned off the system and on again waiting for the worst.... Humph, for the next 5 tries I was given a blue screen.. In other words, the system was unable to boot or no program was running at all.

I started to speculate what could be causing the problem, so the first thing I thought was to try to dissipate any possible charge stored in the caps involved with the encryption circuit. Tested the board, but no change.

Second, I checked the PRG roms for integrity and everything was OK.

Third, I placed the Razoola PCB tester ROM and from this point on I knew it was really something more tricky/serious than I was expecting as the system didn't boot anyway. I grabbed my logic tester once again and focused on the PROGRAM section. It could be something related to the Q-SOUND program also (ROMS 1 and 2), since the system won't boot if the Q-SOUND can't be initialized, EVEN USING RAZOOLA PCB TESTER. But this was discarded since there was sufficient activity in the address pins or the expected logic state at least in pins such as OE(-) and CE(-) and WR(-), the control pins.

So, probing around the main program area I quickly found the OE(-) pin of every program ROM just floating. All OE(-) pins of all program ROMs are tied together and I ended up tracing it back to the pin 12 of a 74LS245 three-state output bus transceiver, at region 10F, that simply controls the bus for the main program.

 

20170506_160906.jpg

 

Pin 1 of this IC defines the direction for the bus, depending on its logic state. In our case, it was well defined since it was tied to VCC. If it was HIGH, then the bus direction was set from A to B. Pin 12 (B7) was and output, a floating output.

Pin 19 is the G(-) or CE(-) and it was LOW as it should.

Pin 8 is the A7 and it is the input for the B7 output, and its state was HIGH. Since the chip was enabled, this pin should be at least HIGH (as everything should be pulsing), not floating.

Made a small surgery by replacing this suspicious 74LS245 for a brand new one and...............

Problem solved! One more CPS 2 B board brought back from the dead.

The board booted normally and I played through the game from start to finish with no issues.

 

20170506_161655.jpg

 

I rank this an easy fix. :D

Edited by KAISERSIGMAX3
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