Sound problems with The Great Ragtime Show

[stt1]

Symptoms:

Music partially missing, also all "speech" parts missing. Only R-VOL potentiometer changes the volume, on both channels. L-VOL potentiometer has no effect at all.

An example from Youtube: https://www.youtube.com/watch?v=nLwB1ZdZN_0&feature=youtu.be&t=167

Missing compared to the youtube-video:

"The Great Ragtime Show" -speech (when the brown picture of airplane and pilot scrolls to screen) and all the applauses (during the pilot running animation is shown)


What I can hear from the PCB:

Short propeller/copter sound (~1-2 sec)
One short shooting effect


When the game runs, I can hear sound effects, or at least most of them, musical parts are missing a lot - they sound mostly "flat" and bass-oriented.

Done so far:

Measured the potentiometers, they seem to be ok.
Audio amplifier (Toshiba TA8205AH) changed, did not help.


I have found information that this PCB has YM2151 for the sounds - didn't find any such chip, just one (has markings 3569 9221S C13680R on it) which I suspect being one, next to the audio amp. See the attachment, please.

This PCB has also another audio-chip (PSG sounds?) - Hudson HuC6280A


Does someone have an educated guess which one of these would most likely cause the problem?

Would the oddball (3569...) chip be YM2151?

Any other ideas to check around?

 

[caius]

The Hudson HuC6280A is the CPU which commands the whole digital sound system, if you get some kind of sounds then it's good for sure.
The IC marked "3569 9221S C13680R" is nothing more than a rebadged YM2151, manufacturers often use these compatible parts for cost saving.
I'd say your fault is located in the circuit made of the two OKI MSM6295 and ROMs storing the samples.If you have an audio probe you can simply "listen" to the analog output pin (of the internal DAC) of the two OKI to see which one is outputting bad audio.Anyway, it a very simple issue to fix.

 

[stt1]

Thanks a lot.

Yes, I really think this can be fixed, just needed this kind of more educated comment to narrow down the possibilities. Noted also pair of OKIs (M6295, SMD-version) last night, they are located next to jamma-connector.

Unfortunately no audio probe nor oscilloscope at the moment available, but I'll figure something out.