CPS1 mainboard missing sprites

jepjepjep

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I recently picked up a CPS1 board, where it is missing sprites. It was originally a UN Squadron and the ships (player and enemy) don't show up. I switched the A-board with a different working board and it plays fine. Now when I try to run my Final Fight board with the UN squadron A-board, none of the player sprites appear either.

Any idea what part is responsible for displaying the player sprites so that I can fix this mainboard?
 
Either a logic chip fault or, more than likely, the custom chip on the main board.

To be honest, CPS1 main boards are such a pain to repair that it would probably be best to buy a working main board.
 
If I don´t misundersand, it don´t show sprites in the good mainboard of UN squadron with the Final fight A board... then some of the roms in there must be wrong, you should try to verify every rom with the mame image or get a working Final fight A board to compare the roms
 
If I don´t misundersand, it don´t show sprites in the good mainboard of UN squadron with the Final fight A board... then some of the roms in there must be wrong, you should try to verify every rom with the mame image or get a working Final fight A board to compare the roms

Please stop trying to diagnose things. the problem is following the A board according to the OPs description. The ROMs have nothing to do with that as they are on the B board.

CPS1 boards are odd in that I do not trust their "RAM OK" self diagnostics. You either have a problem with the Video RAM, the chips buffering the Video RAM, or the big custom chip on the A board.

The problem with fixing is is getting to the chips to check them. I had plans to build some simple extension cables to make it possible to get a logic probe on the A board, but those things are so cheap it didn't make sense to spend a lot of time learning the board to that level of detail.
 
The problem with fixing is is getting to the chips to check them. I had plans to build some simple extension cables to make it possible to get a logic probe on the A board, but those things are so cheap it didn't make sense to spend a lot of time learning the board to that level of detail.

I'm always thought that it would be useful to have some simple test logic on some small, connected boards that plug into all four of the interboard connectors on the main board. Should be easy enough for someone with PCB design and programming skills. :) That way all of the main board could be easily accessed while some basic test programs are running, so many diagnosis so much easier.

There are so many CPS1 main boards failing of late (I must have ten!) that such a thing would be a very useful diagnotic tool. I know they're relatively cheap to replace, but one day people will be crying out for working main boards.
 
Thanks for all of the info guys. I think this repair is far beyond my skills. It's such a shame that a working game has to be sacrificed in order to get a repair due to these faulty A-boards. I now have 3 games with dead A-boards :( and working B&C's.
 
If any of your faulty A board have no sound as their only fault then replace the Z80, thats by far the most common reason A boards ended up as scrap. Other than that they are not simple boards to work with.
 
For the flexy one, check the solder joints on the crystal oscillator, metal tin, four legs, often not great solder joints.
 
Also, check the custom chip on the flexy one. It's surface mount and a good drop could've popped some of the legs loose from their solder joints.

When we have the repair party at my new shop I'll show folks how to reflow surface mount chips with a standard iron and some liquid rosin flux. :)

Raymond
 
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