Contradicting the current tendency to sell all the CPS1 stuff due its extreme unreliability (my mate Porchy knows something about…) I decided to buy a faulty CPS1 motherboard (also know as  ‘A-BOARD’).Seller claimed board was good except for the audio completely missing.

When the board arrived (it was actually a ‘CPS DASH’ so the last revision with 12MHz oscillator), I immediately noticed it was missing the volume pot:

So, I took this pot (2.2KOhm to be exact) from a dead CPS1 motherboard sure that this was the cause of the missing audio.But I was wrong since still I got no audio.Touching with fingers the solderside pins of the HA13001 main amplifier gave me some noise from speakers so fault was elsewhere.

First I started to test Z80 audio CPU with my logic probe and no activity was present on data/address lines.I knew from other CPS1 repair logs that bad Z80 CPU is a very common fault on this boards so I decided to replace (using a round machine-tooled socket) it without thinking twice.

And this was enough to restore full sound back.

Got this PCB as usual from Ebay as faulty, seller said it was missing some sounds.PCB was in a clean state:

Once powered up, actually, all sound FXs were present but music was missing at all.Sound hardware is formed by a Z80 CPU which controls a YM2203 FM synthesis IC coupled with a YM3014B DAC and all sound (music+ FX) are pre-amplified by a NEC uPC4556C OP-AMP before going to  the main MB3735 amplifier.Connecting the analog output (pin2) of the YM3014B to an external amplifier I could hear the music, this was still present on the OP-AMP input (pin5) but not on the output (pin7).So, I desoldered it and tested it in my chinese tester which reported it as good.But this did not convince me so I replaced it with an equivalent Mitsubishi M5218 and this was the winning move since music was fully restored.

End of job, see you next repair!