MAME cabinet picture is off-center horzontally.

[Shaddycat]

I'm putting together a MAME cabinet with a spare PC board and components I had lying around.  It's hooked up with an Ultimarc ArcadeVGA and a J-Pac.  The monitor is a Wei-Ya Makvision M3125.  I have Groovymame installed as well.  I get the happy lights on the J-Pac saying it's all synced up, and the vertical sync is working just fine.  However, I'm having an issue where the image is off center to the right, and if I adjust the H-Pos pot, the image turns to garbage.  No matter how much I adjust H-Hold after that, I can't get the picture back without putting H-Pos back to where it was before.  The last time this monitor was working was maybe about a year ago when I had a Pandorabox DX hooked up to it, which had good image.  Unfortunately I don't have the Pandora available for me to test with again, but I'm trying to get my hands on it. 



Video above of the issue.  You can see when the screen turns to garbage is when I adjust the pot labeled H-POS.  Then at the end when the image shifts back and forth but is clear, I'm adjusting the H-Hold pot. 

Any help is appreciated, I'm a bit of a newbie! 

Edit: The H-POS pot was worn out and after replacing it, the issue was fixed.

[Zebidee]

The pot is just doing what it is meant to do.

H-Hold, or horizontal hold, tunes your monitor into the horizontal sync signal. It usually has just one good position. When you adjust it, monitor goes out of sync!

Most monitors will have another pot called something like H-POS, or horizontal position, and/or H-WIDTH, obviously for wider/narrower. You want these pots.

Because you're a noob, a warning: If your monitor has a H-WIDTH adjustment with a ferrite core and a hexagonal hole (you'll know what I mean if you see it), DO NOT attempt to adjust it with a screwdriver or other metallic tool. That will likely break it. There are special plastic tools cheaply available online for this stuff; I've made some before by trimming back plastic tweezers or a pen lid.

EDIT: Obviously you found the H-POS pot already - maybe the pot is a bit worn out. That does happen over time as the carbon film inside is eroded slightly every time you adjust it.

[Shaddycat]

The pot is just doing what it is meant to do.

H-Hold, or horizontal hold, tunes your monitor into the horizontal sync signal. It usually has just one good position. When you adjust it, monitor goes out of sync!

Most monitors will have another pot called something like H-POS, or horizontal position, and/or H-WIDTH, obviously for wider/narrower. You want these pots.

Because you're a noob, a warning: If your monitor has a H-WIDTH adjustment with a ferrite core and a hexagonal hole (you'll know what I mean if you see it), DO NOT attempt to adjust it with a screwdriver or other metallic tool. That will likely break it. There are special plastic tools cheaply available online for this stuff; I've made some before by trimming back plastic tweezers or a pen lid.

EDIT: Obviously you found the H-POS pot already - maybe the pot is a bit worn out. That does happen over time as the carbon film inside is eroded slightly every time you adjust it.

I suppose what I am confused about is why is the H-POS pot turning the picture to garbage/throwing the image out of sync when adjusted, when the H-HOLD moves the picture back and forth slightly?