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MUTE ST-V BOARD: WHERE TO BEGIN WITH TROUBLESHOUTING?

cyllboy

cyllboy

Student
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Jul 30, 2020
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Italy
Hi to everyone, my ST-V has no sound: I just checked the onboard pot and it is ok. Where do you suggest to begin with testing?
No sound at all, even tried to get from the aux pins (line level out) on the board.

Do you think that recapping coul be any good? I checked some of the capacitors and they seem to be ok (tested ESR)...


Thank you everyone!
 
Recap never hurts.

Check the TDA1386T chip (datasheet available here) shows pin 18 (left channel), 21 (right channel) from my notes. I harvested one of these chips from a dead Sega Saturn and fixed audio issues before. I would logic probe those pins for activity to start.

1614874723791.png
 
Thank you very much! The data sheet will be very useful for that!
 
everten said:
Recap never hurts.

Check the TDA1386T chip (datasheet available here) shows pin 18 (left channel), 21 (right channel) from my notes. I harvested one of these chips from a dead Sega Saturn and fixed audio issues before. I would logic probe those pins for activity to start.

1614874723791.png
Click to expand...
I Logic-probed the pins and they are both stuck to hi: I should have a pulse instead or am I wrong? Probe is set to ttl
 
They're probably not 'stuck', but rather constantly outputting analog signal.

Try switching to CMOS just when probing pins 18 and 21. It will produce the same results except without the constant high pitch noise (at least on my probe). What you will hear from the probe speaker is the analog audio signal. It will sound horrible, but you should recognize sounds and music. Note there will be periods without sound and music in attract mode so it's probably best to coin up on a game where you know there is music.

Pin 6 on that chip looks like the digital input, so probe that in TTL mode - it should be pulsing.

If the input and and outputs probe good your problem is likely elsewhere.
 
I'm currently also dealing with a mute ST-V board. The TDA1386T chip was in bad shape when I checked it (thanks to this thread), and there was obvious evidence of someone making some sort of horrible repair attempt. Gobs of solder, several legs were damaged, and some seemed like they were accidentally lifted. My logic probe showed no activity from pin 18-22. After cleaning up the crappy solder job, I tried testing the board again, but there's still no sound unfortunately.

Developer test mode shows no issues with Sound Ram, so I don't think replacing the 315-5833 GAL will do anything for my board.

My next step is to order a "new" TDA1386T off eBay and replace my damaged one. Hopefully whatever shows up works, since I'm basically blindly ordering a discontinued chip from the 90's.
 
An update on this.

I replaced the TDA1386T with the sketchy one I got from eBay and unfortunately, the board was still mute. However, I also installed the Everten stereo+CPS2 kick PCB, and I do get sound from the RCA jacks. The volume pot doesn't seem to work on the stereo jacks, so the ST-V just stays at 1 volume level.

I don't really understand why the board is mute on mono/JAMMA edge, but given that all of my cabs and supergun setups are stereo capable, I guess that's fine with me.
 
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