Capcom CPS1 no sound

[MaRC]

Hello, people.
I received a 1.5 board from Aliexpress with the audio part mostly taken from a 1.0 donor board. The main chips are all original, not clones, including a Yamaha, a Z80, and an audio amplifier. Over time, the sound began to disappear and reappear if the board was left for a couple of hours. Eventually, the sound completely disappeared, and now when I supply power, I hear random sounds or music. If it's music, it continues playing until I turn off the power. The issue is related to the digital part. I tried changing the B+C boards - SF2CE and 87 in 1 with different games, I looked at the tracks up to the EPROM, I checked the power supply, the clock frequency of the 3.5 MHz clock generator, and I replaced the audio RAM, the z80, and both ls374s, but this didn't really change the situation. The only problem is with the sound - the graphics are drawn without any issues, the buttons are working, and the games are running. What should I do next, should I replace the 68000?

 

[sukhbir]

Hello, people.
I received a 1.5 board from Aliexpress with the audio part mostly taken from a 1.0 donor board. The main chips are all original, not clones, including a Yamaha, a Z80, and an audio amplifier. Over time, the sound began to disappear and reappear if the board was left for a couple of hours. Eventually, the sound completely disappeared, and now when I supply power, I hear random sounds or music. If it's music, it continues playing until I turn off the power. The issue is related to the digital part. I tried changing the B+C boards - SF2CE and 87 in 1 with different games, I looked at the tracks up to the EPROM, I checked the power supply, the clock frequency of the 3.5 MHz clock generator, and I replaced the audio RAM, the z80, and both ls374s, but this didn't really change the situation. The only problem is with the sound - the graphics are drawn without any issues, the buttons are working, and the games are running. What should I do next, should I replace the 68000?

Have you checked the DAC (ym3012) at location 11C?
this often fails ,check with a scope the digital signal going in and the analogue Coming out,if that’s ok then check the opamps.
good luck

 

[MaRC]

Have you checked the DAC (ym3012) at laction 11C?
this often fails ,check with a scope the digital signal going in and the analogue Coming out,if that’s ok then check the opamps.
good luck

If there was a disjointed set of sounds at the output, then the problem might be in the DAC, but the problem is that the sound, when it appears, is a random sound sample or a music track from a game. This means that the z80 is either receiving incorrect commands from the 68000 or processing them incorrectly. The z80 receives commands from two ls374 chips, which I have replaced without success. According to the scheme, the commands before ls374 pass through A4 IOAI - it may be faulty, but there is nothing to replace it with. After that, only 68000 remains

 

[Ace`]

The Z80s die on these because Capcom fitted a standard Z80 but it should have a Z80A.

 

[sukhbir]

The Z80s die on these because Capcom fitted a standard Z80 but it should have a Z80A.

He's said the z80 has been replaced.

 

[Ace`]

With another Z80 and not Z80A by the looks of it. I've also had a bad crystal in the sound section cause that issue, where it works for a bit then cuts out.

 

[MaRC]

The board that was sent to me had a 6mhz z80, and I replaced it with a 10mhz one, but it didn't make any difference. The random sample or music plays when the board is turned on, and it plays the same way if you reset the Z80 by shorting pin 26 to ground. The sound only changes if you turn off the power for a few seconds. Of course, I also tried different power sources and checked the incoming voltage on the board, which was stable at 5 and 12 volts.

 

[TheDaddy]

Thses are a pain as other say , Looks like you done a lot. My first thing would be Z80 & Ram and you already done that. Agree with Ace they put really cheap Z80 in there and I replace with the Z80A as well.

It may be ........



Good Luck ,

Dave.

 

[MaRC]

z80a is just a designation for a z80 that can run at 4mhz. I replaced the installed 6mhz with a new, tested one from old stock that can run at 10mhz. The processor is less hot, but it hasn't changed the situation. Again, it seems that the z80 is receiving incorrect commands. The commands from the 68000 are passed through the PAL A4 IOAI. Initially, the 1.5 board had a different firmware, as the sound works differently in it, and it's obviously now being flashed by the Chinese. How can I check this, and can I buy a clean chip and flash the necessary firmware myself?