Nanao MS9 acting weird

[Mokum]

So, I've got this vertical NAC. Everytime I plug a vertical game (tried 3 Psikyo shooters so far) I get some noise coming from the speakers (Strikers 1945) and, when the screen is brighter, the image trembles a little bit emitting some tiny noise as well (Strikers 1945 II and Gunbird 2).
After a while (like a game lasting about 20 minutes) the image's issues seem to cease.
The odd thing is... when I plug an horizontal game nothing of this happens! I've tried with Double Dragon and a KoF '99 MVS cart so far.
I then tried the vertical shooters on my friend's NAC and he got none of my issues.
How's that? Why does my monitor act weird with vertical games only? Is there any pot I can use to try and adjust anything helpful?
Thanks.

[Asayuki]

*sniff* *sniff*
Power supply
*sniff*

[Mokum]

*sniff* *sniff*
Power supply
*sniff*

Ok. But why does it only affect vertical games? I know this sounds crazy but I've got absolutely no issues with horizontal ones!
Is there any pot (on the chassis, neck board, I don't know...) I can try and see if it might fix my problem?

[zak]

*sniff* *sniff*
Power supply
*sniff*

Ok. But why does it only affect vertical games? I know this sounds crazy but I've got absolutely no issues with horizontal ones!
Is there any pot (on the chassis, neck board, I don't know...) I can try and see if it might fix my problem?

Have you tried a vertical game in horizontal orientation (i.e. without rotating the monitor)?

[Mokum]

*sniff* *sniff*
Power supply
*sniff*

Ok. But why does it only affect vertical games? I know this sounds crazy but I've got absolutely no issues with horizontal ones!
Is there any pot (on the chassis, neck board, I don't know...) I can try and see if it might fix my problem?

Have you tried a vertical game in horizontal orientation (i.e. without rotating the monitor)?

Not on my cab. I've tried the vertical games on my friends' NAC, which is horizontal, and they play just fine.

[zak]

Does your cab have a working light bulb?

[Mokum]

Does your cab have a working light bulb?

Nope. I've installed one but it lacks the starter. Anyway the problem was there even before installing the light bulb.

[Asayuki]

Ok. But why does it only affect vertical games? I know this sounds crazy but I've got absolutely no issues with horizontal ones!
Is there any pot (on the chassis, neck board, I don't know...) I can try and see if it might fix my problem?

Well, you have to admit that we don't have much information to base an opinion onto.
You might have issues with the power supply, which is causing some games to output glitched sync signals, or you might have an issue with voltages inside the monitor (again, power supply). For what we know, your games being vertical or horizontal might be just a coincidence rather than a cause...

EDIT: Oh, and let's not exclude proper grounding of the monitor. That can also be a possibility.

[grantspain]

strange fault,where is the video ground wired to on the jamma interface

[Mokum]

Ok. But why does it only affect vertical games? I know this sounds crazy but I've got absolutely no issues with horizontal ones!
Is there any pot (on the chassis, neck board, I don't know...) I can try and see if it might fix my problem?

Well, you have to admit that we don't have much information to base an opinion onto.
You might have issues with the power supply, which is causing some games to output glitched sync signals, or you might have an issue with voltages inside the monitor (again, power supply). For what we know, your games being vertical or horizontal might be just a coincidence rather than a cause...

EDIT: Oh, and let's not exclude proper grounding of the monitor. That can also be a possibility.

You're right but I really dunno what more I could tell you about it...
I will test another vertical and horizontal pcb's and see what happens... but I need to borrow them from my friend so I will take a few days...
Wanting to test a diffeent PSU, where I can get one? I've browsed a bit and kind of found none...

[Asayuki]

I guess measuring B+ at the monitor doesn't hurt. As for the power supply, would it be possible to power the game alone from just a random arcade PSU? You know, the ones which go cheap enough on ebay more often than not like this one for example: http://www.ebay.de/itm/5V-10A-12V-5A-5V ... Sw8gVX3mQI Not meant as a definitive replacement but rather as a test to rule out one of the components.

[Mokum]

Yes, I was thinking about such a cheap PSU actually.
I'll give a try. The one you linked should do the trick.
On a couple side notes: how do I measure B+? Also, are ground wires ok?

[ebinsugewa]

Test at C953 I believe, should be about 75V.

[Asayuki]

Also, are ground wires ok?

Most metallic parts are going to be connected through grounding cables. You can ensure that those connections are present and stable. Grantspain was also suggesting to check video ground (pin 14, parts side) which is very important to reduce noise and sometimes to even allow the monitor to lock to the signal.
I personally know of a lot of bootlegs which leave such pin of the jamma edge unconnected. In this case, depending on how the cabinet is wired up, ground has to reach the monitor through a much longer path through the power supply and this creates all sorts of issues. This might well be the difference between one cabinet and the other and between one board and the other.
Let us know what you find.