MVH4 No sound with weird mod

[juanchomvs]

Hi forum

I recently purchased a 4 slot mvs that according to the seller had only a sound issue. I think is a z80 issue or a ym2610. the thing is once I inspected the board I found some interesting things...
I am not expert but I dont think these things should be there. Can someone tell me what kind of mod is this? I dont think this was made to repair something. Please help I am just a newbie

[juanchomvs]

Sorry this might help
Do you think this has something to do with the sound issue?

[ack]

Those are both common/factory mods. I have many MV4 boards with them.

[juanchomvs]

Those are both common/factory mods. I have many MV4 boards with them.

That is good news! Thank you for your response
I’ll replace the z80 chip and see if that fixes the audio

[sr20det510]

That is good news! Thank you for your response
I’ll replace the z80 chip and see if that fixes the audio

Have you tried a recap kit to fix the audio in your board?

I think that is usually what causes the audio to eventually go out.

[juanchomvs]

No jet do you advice to do a recap before I change the z80?

[RyuX]

What kind of sound issues are we talking ? Do you get distortion or parts of the sound missing - or are you missing all of the sound ?

The Mod on the Pro-B0 is bypass capacitors to ground to filter the WR1/2 and WR2/1 lines (it seems).
The other mod on the LS161 is a pulldown resistor (to ground) to bring down the signal on the QA Output of the counter.

I don't have the details of why they needed to mod this but I am pretty sure it was just to bring the signals within the tolerance range.

[juanchomvs]

I get no sound at all. Its completely dead

[RyuX]

Ah I see.. I am no expert with the MVH4 but are you sure that your power supply has the 12V Line properly connected and working ?
Do you get any sound pre-amplifier circuit ?

[juanchomvs]

Yes the 12v line is properly connected. I get no sound at all thru the head phone jack or jamma Adapter. I bought a cap kit is arriving on Monday paid $10 for it if it does not fix the audio is ok I can simply change the z80 and see

[juanchomvs]

Ok so I had a problem with the cap kit shipping is pending and I just couldn’t wait
I changed the z80 chip and now I get some sound but some tones sound awful
And the rest of the music is ok

What do you think is the prob?
A capacitor ?

This is what I hear
https://streamable.com/2pcsh7

So there is some improvement

[Neo Alec]

Ok so I had a problem with the cap kit shipping is pending and I just couldn’t wait
I changed the z80 chip and now I get some sound but some tones sound awful
And the rest of the music is ok

What do you think is the prob?
A capacitor ?

This is what I hear
https://streamable.com/2pcsh7

So there is some improvement

What does it do with a real cart? That sounds like a problem with the game to me.

[juanchomvs]

What does it do with a real cart? That sounds like a problem with the game to me.

Is not a cart prob all games sound like that. I have working 1 slot and they sound fine

[juanchomvs]

*Update* I finally received the cap kit!
I have now replaced all caps. I also removed the resistor on the chip since there was no noticeable difference with or without
But sound is the same...

Should I start checking for bad ym2610?

Please help almost there...

[juanchomvs]

Ok i received the chip today “ ym2610 “from China. I installed it and now werks!!

Thanks for your responses
��

[Jonap]

Nice to see the motherboard works again! always is good news saving old retro material!.