Hantarex mtc 9110 vertical sync problem

[ginocomino]

Configuration : Hantarex mtc 9110 monitor (old cabinet)
j-pac
vga arcade 3000

the original game  ran perfectly, but as soon as I connected j-pac,arcade vga 3000 and my pc it was impossible to keep the image stabilized vertically. I changed the v-sync 10k potentiometer with a new and better one but same result... as soon as the image looks stilll after few seconds it starts to roll upwards....
any hint?

I have googled around and found many people with the same problem but couldnt find a solution
TIA

[grantspain]

there was an old trick with hantarex monitors whereby you attach a 5k resistor from vertical sync to ground on the video input plus

[ginocomino]

there was an old trick with hantarex monitors whereby you attach a 5k resistor from vertical sync to ground on the video input plus

I read about it

http://forum.arcadecontrols.com/index.php?topic=86606.0

but it sounds like a "work in progress", not a final solution...