Problem with Hantarex (polo?) 25" of 1991

[trick72]

Hi,
I have a mame cab and i'm using the original hantarex monitor in combination with a J-PAC. Some games (it is certain resolutions) run perfect on this screen, but for some games like most neo geo games, the screen displays "garbage" or part of the bottom of the screen is displayed at the top (see screenshots). the picture is stable (it's not rolling) but is displayed like on the screenshots. It's strange to me that the screen is incorrect *only* during certain parts of the game, for example, with InsectorX, only the title screen displays incorrect (like you can see in the screenshot), but when the actual game itself starts, the screen somehow "clicks" correct and stays correct during the game. For Metal Slug, it's also during the attract mode and on some parts during the game that the monitor displays the picture incorrect. I have tried to run on advanceMame in dos, or in Windows XP with soft-15khz, all the same. I also tried different video cards, without any luck, so it's really a monitor issue. When I put the same PC in my second cab, I don't have this problem.
I also tried to run InsectorX on a higher resolution than it's own and than I don't see the problem either and the screens are fine (ofcourse too small because of the higher resolution, but not garbled up). So it's clearly a problem that only appears on *certain* resolutions for this monitor.

Any idea's if this is fixable?

screenshots comments:
1st screen: during the display of the highscores in metal slug, the screen "pops" into this incorrect mode
2nd screen: during the title screen of metal slug, the screen "pops" into this incorrect mode, but afterwards when I play the game the screen is correct again.
3rd screen: the title screen of insectorX is all messed up. please note: it is a stable picture, not rolling.
4th screen: but ingame, the display is correct again.

[grantspain]

snk neo geo needed the vertical and horizontal sync linked on arcade cabs or you would get the problem you describe,if you have a hantarex polo there will be a seperate vert and hor sync wire on the video input plug

[trick72]

Okay thanks for the answer.
That makes sense and it sounds like something that a newbie like me should be able to fix 
So if I understand correctly, I should be able to find a "loose wire" in the cab for hsync (or vsync) that I should connect to the composite sync pin of the jamma connector together with the currently attached wire?
I'll check it this evening
Thanks

[grantspain]

pin 5 is horizontal(composite sync)
pin 6 is vertical sync
this is at the green video input plug on the monitor chassis
1991 is very early for a polo chassis,are you sure its not a mtc9000

i think the mtc9000 had a sync switch on the chassis(last one i worked on was about 10 years ago)

maybe a photo of your chassis will help move things on a bit

[trick72]

Hi grantspain,
yeah it's possible that it's a mtc9000 rather than a polo.
you were correct, it certainly was the vsync which was not set correct. I found a vsync knob which I could turn left/right. although the picture was stable on most games, It seems that I had to turn this knob even more counter-clockwise for these specific neo geo games to be displayed correctly too. So it was an easy fix after all.

While looking at the chassis, I indeed noticed a "switch" on the board which was in the "down" position. But this was not labeled on the system board so I didn't want to touch it before i'm sure what this is. Maybe that was the sync switch you mentioned...

However, the problem seems to be solved now by the further adjustment of the vsync dial knob.
So thanks for pointing me in the good direction

I have another cab with exactly the same type of monitor (also a hantarex of 1991) but I opened a new thread for that since it's a different problem I have with that screen. 

thanks