Help with Neo Geo MV25UP-0

[mob-z]

Hello Arcade enthusiasts,

I've recently was able to get my hand on an MV25UP-0 Japanese 6 slot arcade. And I'm currently in the process of refurbishing the whole thing starting with the wiring.

I have fired up the arcade and it seems to be working. My current issue is that once I plug in my 6 slot mobo, the screen turns to squares and the system main screen doesn't show. I know some might think that the issue is with the board, I have tested the board an an external device on my tv and it worked flawlessly. I have tested all 6 slots and the games seems to change from one another without any issue. When turning the arcade on, a buzzing sound comes from the speakers and the screen is what is shown below.

The arcade has all original parts, which have not been changed since. I've had substantial help from BuddyC here at this forum, and I have been talking to him regarding this issue. He pointed out that it could be a wiring problem that is limiting the board from getting enough voltage (5V). Or it could be another issue? I would appreciate some input as to get this thing working again. Thank you.

 

[nem]

Have you measured voltage at the edge connector?

 

[mob-z]

I just measured it and it is extremely low. I am not very friendly when it comes to electricity. I've had my fair share of shocks .

The measurement reads 3.59V.

I have a new 5V/12V power supply that I haven't used yet (bought from retro arcade.us) not sure about its quality though.

I have bought one from arcadeworld UK (thanks to BuddyC) but it's still on its way which might take a while.

For the time being, I will test it with the one I have and post back for any updates.

 

[mob-z]

I have tested my other power supply and the voltage reads V4.20 which is insufficient to even make it work. Nonetheless, now I know atleast what my current issue is.

 

[nem]

The original CSK power supply is a very good little unit. I wouldn't replace it.

There's a small adjustment knob at the top, V. ADJ. You will need to adjust it. Turn it a bit clockwise, then measure your voltage. Repeat this process until you (hopefully) hit around 5.05V.

 

[mob-z]

Nem,

Thank you for your input. I tried rotating the little knob but it seems that it is going clockwise (or counter clockwise) nonstop? I would assume that there would be an end lock of some sort so it would move any further?

 

[nem]

Sounds to me like it's broken. It should turn around 270 degrees. That could explain why you're getting the bare minimum voltage out of the PSU.

 

[mob-z]

Yes indeed. I have spare original power supply that I could try as well. I'll try it tonight and see how it goes. Thank you Nem.

 

[mob-z]

A quick update on the issue. I have measured the voltage when put underload and without any load (i.e. Plugging in the motherboard) in both cases. The voltage is showing as 3.60V. This using the original power supply.

After changing the power supply (attached), without any load the voltage reads 4.30V (setting voltage to highest at counter clockwise), while with load it is reading 3.60V.

I am puzzeled at this stage as I am uncertain what causes the voltage to decrease. Any help would be appreciated.

 

[nem]

That is really odd. What does your AC voltage show? Measure at AC/L and AC/N with multimeter set to AC.

 

[thegreathopper]

It’s the load and a 6 slot is a big load, it draws quite a bit of current.

 

[mob-z]

That is really odd. What does your AC voltage show? Measure at AC/L and AC/N with multimeter set to AC.

It reads 50V solid. I tested also the same thing with the new power supply and both give the same reading.

 

[mob-z]

It’s the load and a 6 slot is a big load, it draws quite a bit of current.

It does, my. Only issue is with the power supply. It is nowhere near 5V. Even without any load it gives 4.3V (newer power supply) which is too low for a 6 slot to even work.

I can rule out that the original power supply is faulty because even when turning the adjustment needle, it always staysbat 3.60V

 

[nem]

That can't be right. Did you put the meter leads on AC/L and AC/N and set the multimeter to 200V AC (V with a wavey line over it)?

It’s the load and a 6 slot is a big load, it draws quite a bit of current.

That's not it.

 

[mob-z]

That can't be right. Did you put the meter leads on AC/L and AC/N and set the multimeter to 200V AC (V with a wavey line over it)?



That's not it.

I am certain that I did it correctly. I am also. Skeptical about this, which lead me to check the wiring to see if I missee anything.

Let me recheck just incase I made a mistake and I will confirm the AC voltage reading.

 

[nem]

If you put one meter lead on Earth ground (like you were measuring DC), you would get 50V (provided your AC input is 100V).

What kind of transformer are you using? Saudi Arabia is 230V, correct?

 

[mob-z]

If you put one meter lead on Earth ground (like you were measuring DC), you would get 50V (provided your AC input is 100V).

For the leads, one is set to the N while the other on the L. This gives me a solid 50V.

I am using a voltage regulator and plugging in the 110V output to power up the arcade. (attached)

What kind of transformer are you using? Saudi Arabia is 230V, correct?

Yes it is 230V. The one inside the cabinet has a transformer that reads 220V which really confused me. I dont want to assume that it is safe to plug it in 220V AC? I know Japan uses 100V AC and hence I'm always using with the stablizer.

 

[nem]

A-ha, you're using an external transformer. You can see from your photo that there's an internal stepdown as well. Two transformers will explain the 50VAC you're seeing.

Plug it without the external transformer.

Maybe unplug the monitor from the cab, just to be on the safe side.

Measure AC on the PSU again.

 

[mob-z]

A-ha, you're using an external transformer. You can see from your photo that there's an internal stepdown as well. Two transformers will explain the 50VAC you're seeing.

Plug it without the external transformer.

So plug it directly to the 220V AC?

Maybe unplug the monitor from the cab, just to be on the safe side.

Yes I will do that just to be safe.

Measure AC on the PSU again.

Let me do that and get back to you .

 

[thegreathopper]

Haha 2 step downs that will do it, no wonder your volts are low.