Now that I soldered a couple of sockets I can swap them easily if it's necessary
Is the sound totally missing?If yes, the problem is most likely in the digital circuit.You can use an audio probe to troubleshoot the issue by listening various point of analog and digital circuits
If only the music is missing and effects present, the problem should concern the two YM3438 OLP chips as the sound FXs are generated by the Ricoh RF5C68A (remarked ASSP).
No sound is missing, all sounds (compared to some videos on the web) are playing.
The only issue is that when there is only SFX or noting played at all I have a quite strong "hiss" noise that changes its intensity according to how many and wich colours and images are on the screen. When BGM is playing I don't have any nterference (at least not perceptible)
Understood.You can try to replace the Ricoh RF5C68A but problem is the chip is really hard to come by unless you will take another one fron a not working System18 (or System32) motherboard
That's really interesting but unfortunately System 18 are quite uncommon (never looked for a broken system 32) if the issue is from this component I fear that I'll never be able to fix this board
I'm not saying that it's not hard to find I trust you since you have a lot of experience . I'm just saying that probably I'll not be able to find one.
Maybe if you happen to find one please let me know please
if it responds to the picture then a bodge would be to isolate it's power line and filter the hell out of it.
it's not uncommon in professional systems to have a seperate voltage regulator for the sound circuit, to isolate it from the logic.
Today I received the OP-Amps:
I've swapped them but there's always the same noise.
I've also noticed (it's present with both old and new TL064CN) that if I touch the top of the capacitor C31 the noise increases as shown on the video (don't know if it's normal though).
I was meditating to replace the audio AMPLIFIER MB3733 but I don't know if it's a good idea (I can try to swap this one with the ones on my S16B and s24 but I think that is better if I buy a new one even if the only one at a fair price comes from HK so I'll need to wait more than a month to receive it...) What do you think?