Another MVS sound issue

Alright, so I had a 1-Slot board on which the sound totally disappeared one day. Picked up a 4-Slot board to replace it and - imagine that - no sound there either. While the 4-Slot was running, I checked for anything coming off the headphone connector pins and got nothing (originally, I was running from the headphone connector, into a receiver, and through my stereo speakers.) Next, I grabbed wire 10 from the Jamma harness (Speaker + Right) and checked that for a signal. I got just under 12V from it, which I assume is my audio signal. So, I wire this up to a speaker (admittedly not 8 ohm) and get a very faint humming from it. Also, the faint hum will change in frequency along with the action on screen - this suggests to me that it's playing music and sound effects, I just can't hear them.

The questions: is the ohms rating of the speaker something that would cause that much of a difference? Does this sound like typical behavior that would be remedied with an 8ohm speaker? Also, I know that the speaker sound is preamped (I assume, really). If I run that through a receiver and into stereo speakers, as long as I keep the volume on the board very very low, should that work without blowing anything? I was just reading the other thread on sound and a 4-Slot and definitely don't want to get yet another board, especially if this one has some hope. My real desire is that these symptoms are a good sign and it just needs 8ohm speakers.

Is the 12 volts to the board (s) edge connector is OK ?

It is at least where I attach the Jamma harness - are there other areas I should/could check along the way that are critical?

This is a typical HA13001 audio output stage as used on mvs.



You should have 12 volts supply on pin 10.

To check if the problem is before or after the digital to analog convertor YM3016 IC, touch the pins of this chip (with volume full up) if there is a buzz/hum the analog audio stage is probably OK, if not its a digital processing problem, may even be the DAC itself, but really doubt that.

Went through the checks this morning:

- HA13001 pin 10 has 12V
- hum from making contact with YM3016

I also did a little standard cleaning of the board and still no sound. Running the speaker wires from the harness through my component stereo system all produced no "good" sound, though there was faint crackling sound, but very faint at the highest volume and insanely crackly.

What's next? I need my MVS bad

It sounds like a digital sound processing issue, Z80 and or YM2610 or associated memory SM1 & 6116. First thing to check is that there are no open circuit tracks/ dry joints around that area.

OK - checked out all joints and traces for about an hour and found nothing wrong

Any other steps I can take to figure out the problem? It's a little less of a concern now since in the meantime I solved my 1 Slot sound problem, but I'd still love to see that 4 Slot work completely. Thanks.