A couple of issues i have with my MVS U4 cab

[kite]

Hello everyone,
so i finally got a MVS U4 25 cabinet, love it so far
Unfortunately there are a couple of issues with it:

- I only have sound from the right speaker, left is completely silent. Neo Turf Masters sounds fine, but Metal Slug 4 is extremely scratchy. I can't hear anything from the two headphone jacks when plugging headphones into it
- The power supply is buzzing
- Test mode not working. It isn't wired on the MVS connector, but it doesn't work with DIP switch 1 set to "on" as well, i'm not sure if the button has to be wired for that to work
- Setting DIP 7 to "on" doesn't activate free play
- I'm not sure if it's related, but the Neo-Geo splash screen sound is extra- scratchy, even if the game itself sounds fine. I'm quite used to it and it definitely is way less scratchy coming from my consolized 2-slot or the 1-slot i had. The game sounds normal.

On the MVS connector Speaker L and R are wired. Audio mono is not, which makes sense. Correct me if i'm wrong. But the 4F only supports stereo through the headphone jack, so i probably have to mod it to go through the connector as well? I'm just confused because it's my understanding that mono sound is always L and not R, but maybe the speakers are switched around..

I only connected the MVS connector and 8-pin LED connector to the 4 slot to test. I did not connect the memory card board and it's ground wires.
I'm a bit woried about the buzzing power supply. It does sound like ground related buzzing.

Coin button works. Switching games works too.

I was hoping someone can help me out I do have Jamma cabs, but never had a MVS cab.
All in all it doesn't seem to be bad. It plays perfectly.

Thank you very much

Edit// This didn't give me any rest. I want to play some games on this thing after all. I plugged in my consolized 2-slot and it works perfectly fine. Dip switch for test mode works, free play as well.. all... except for the sound still coming from only the right speaker, so that's probably just wired wrong. I also found the test switch of the cab is wired to pin 15(?)

 

[Neo Alec]

I'm pretty sure all 4 slot boards have an MVS pinout rather than jamma standard, and thus output stereo on the edge connector. I believe a lot of the documentation online is from incorrect information on hardmvs.

If the audio issues only affect MS4, that's interesting. You should clean that cart and the slots with Deoxit D5. Otherwise, recapping the audio circuit is the most obvious likely solution.

Put the board in hardware test mode and check the hard dip switches. There could be broken traces or solder joints there.

I would just replace the power supply with a new one. I bought one of these for my rusty noisy one. It's a drop-in replacement and runs quiet:

150 WATT POWER SUPPLY FOR KONAMI AND NEO GEO SNK GAMES [PS-44-1040-00] - $69.00 : TwistedQuarter.com, Arcade Parts Specialist

TwistedQuarter.com 150 WATT POWER SUPPLY FOR KONAMI AND NEO GEO SNK GAMES [PS-44-1040-00] - +5V 15A, +12V 5.5A, -5V 1A UL and CSA recognized External On/Off cable with 4-pin Molex Dual AC input 115vac/230vac, selectable by switch Low ripple and noise, EMI filter Overload and short circuit...

twistedquarter.com

 

[kite]

The sound quality is fine when using my 2 slot, although it still outputs only through the right speaker so i'm guessing that's just a wiring issue.
I tested multiple carts on the 4 slot, cleaned them too.

The 4 slot though.. it should output stereo over the harness, you're right. But it's strange that i don't hear anything through either of the headphone jacks. Someone mentioned that the REAL headphone out is the 4 pin connector next to the two headphone jacks but i am not able to test that at the moment.

I can't put the 4 Slot into test mode at all though. The DIP switch does nothing. I haven't tried rewiring the test button as i'm waiting on my new solder station since my old one apparently doesn't work anymore ^^' i can bridge it though ... The dip switches not working (except the pause one, DIP 8) is strange though.

Would you have any information about how to best change the power supply or is it "just" buying a new switching power supply and rewire it?

 

[Neo Alec]

You have to connect the 4-pin wire from the main board to the memory card board for headphone audio.

To open the hardware test menu:
The cab should also have a test switch inside the front coin door wired through the jamma harness. You could try powering on with that switched as well.

Since you have a consolized board you probably already have a Unibios chip, right? If you have the Unibios installed in the 4-slot, you just need to hold BCD at boot.

 

[kite]

The test switch isn't wired at all to the correct pin on the MVS harness. But yes, there is a test pushbutton, not a switch, in the cab. I can't solder it to the correct pin without a soldering iron though ><

I haven't tried the headphone jack of the cab yet, i can try that.

Yes, the 2slot has a Unibios, but it's about the 4slot. The 2slot works fine.

 

[Neo Alec]

Yes, the 2slot has a Unibios, but it's about the 4slot. The 2slot works fine.

If I were you I would buy another Unibios chip for the 4-slot... for testing and then later, playing.

In the meantime, the bios chip on both boards is socketed, so you can fairly easily gently pull up the bios chip from the 2-slot with a small flathead screwdriver, and then swap out the stock bios chip in the 4-slot with that. That will allow you to continue testing connections using the hardware test menu.

 

[kite]

Argh i didn't realize that.. you'Re absolutely right, i will try that.

 

[kite]

Well at least the headphone output seems to be fine

A question about the humming power supply. Could this be the source of the flickering vertical stripe on screen? There's also some faint humming when it's off but plugged in. After shutting it off, i can hear some clicky noises too.

I've attached videos/sounds of the stripe on screen and of the humming + shutdown noises, if you can/want to have a look at them.

The left speaker.. well, that thing is basically desintegrated. I ordered a pair of the same speakers online to replace it. Wiring checks out.

And thank you all for your help, it is greatly appreciated.