Every single board in this CPS1 stack is defective - repair thoughts please

[hatmoose]

Hi Team;

Had some fun with CPS1 boards this afternoon, swapping around boards and ROMS - unfortunately I didn't make much progress

What I have
1 x Fully working SF2HF' A+B+C stack
1 x very suspect SF2HF' A+B+C stack


As far as I can tell they are very similar but not 100% identical - the working board set has this weird Altera board in socket 20



When I swap the boards round, nothing works
the known good B+C stack boot to black screen with no sound on the suspect A
the known good C boots to black screen with no sound on the suspect A+B
the known good B boots to black screen with no sound on the suspect A+C
The known good A boots to black screen with no sound with the suspect B+C
The known good A+C boots to black screen with no sound with the suspect B
When I take all the known-good chips off the B board and swap for the suspect ones (you guessed it) boots to black screen with no sound

So it's looking like every single board in the suspect stack is bad.
But on the plus side I have an (identical?) fully working set to test against

There is a vast amount of CPS2 repair info out there, but not much about CPS1 - any ideas or pointers on where to start would be greatly appreciated!

 

[ShootTheCore]

When I swap the boards round, nothing works
the known good B+C stack boot to black screen with no sound on the suspect A
the known good C boots to black screen with no sound on the suspect A+B
the known good B boots to black screen with no sound on the suspect A+C
The known good A boots to black screen with no sound with the suspect B+C
The known good A+C boots to black screen with no sound with the suspect B
When I take all the known-good chips off the B board and swap for the suspect ones (you guessed it) boots to black screen with no sound

I agree with your conclusion that every board in the bad stack is bad - your tests were comprehensive. None of the three boards are going to be straightforward to troubleshoot or repair IMHO.

With all three boards, flip them over and carefully inspect underneath for corrosion and trace damage. Use a multimeter set to continuity and check suspicious looking traces for a connection at both ends.

With the A Board, if you have a logic probe check that the 68000 CPU is getting a pulsing signal on the Clock pin. Also check the CPU Reset pin - if the watchdog is functioning at all then it should be toggling the Reset line at power up, and maybe additional times if the game is crashing at boot. The CPU likely won't be accessible from the top with the B+C board in place so you'll have to probe the pins from underneath.

There is a CPS1 Diagnostic ROM set that you could flash to EPROMs and install in the working B+C boards that will run some tests and flag issues if the A Board is operational enough to boot it up.

It's also very common for the custom chips to fail on the A board. If that happens then all you can do is swap them with parts from a donor.

The B board doesn't really have any processing logic - it's pretty much a ROM bank. That said, the game can fail to boot or have graphical issues if the PAL chips are faulty or mismatched, so be sure to swap those over from your working B board in addition to the ROMs when testing. The PALs have been dumped and you can program new ones with files from here:
https://www.jammarcade.net/cps1-pal-dumps/

The C board consists primarily of the large custom chip, and some PAL chips. Again, swap the PALs over from the working C board and see if you get any life out of it. If not, assuming there's no broken traces then the custom chip has likely failed and it'll be cheaper and easier to just buy another C board. @sheep_nova sells them for around $30 USD.

 

[caius]

I think most (if not all) of the A-BOARDs have a bad 'CPS-A-01' ASIC, this chip is very prone to failure.

 

[YesAffinity]

^and c boards are a close runner up if not a tie for custom chip faultiness.