Quick screen roll when screen flashes white on games

[RyuHayabusa78]

I have a Wells Gardner 25k7191 and I'm running games to it through an ArcadeVGA card. I've noticed that when I play certain game where the screen flashes really quickly, like the lightning in the Super Street Fighter 2 intro, the screen rolls really quickly. This happens in other games as well. It's nothing major but it is an annoyance. Any idea what may cause this and how to remedy it? Here are a few vids of it happening. Thanks

[RyuHayabusa78]

Just discovered that it does it badly during the Ninja Gaiden intro when the lightning flashes. It always seems to be when lighting flashes in games that it does the screen roll. Here's a vid of the NG intro. Any ideas?

[RyuHayabusa78]

Hmm, no one has any ideas about what is causing this to happen?

[lilshawn]

maybe your vertical hold is right on the edge of rolling.

give it a few turns back and forth and then find where it rolls one way then turn it until it rolls the other way... set it in the middle of these 2 points.

also check the 50/60hz pot...it's tucked just behind the h-hold adjust

[Rickn]

Yes it could be vertical hold....
If So adjust it so it rolls down and then bring it back till it snaps up and locks.
Chances are that it is related to the B+ supplied to the vertical IC.
I have not looked at the schematics, but if the B+ to the vertical IC is supplied off of a winding of the Flyback, then when the screen flashes, it draws down the B+ and causes the roll.

[boardjunkie]

Sounds like a cap in the Vert section ain't doin' its job so well anymore....

[lilshawn]

i concur, a cap kit solves all sorts of issues. so many caps all do different jobs... it's not uncommon for a monitor this old to need them replaced.

[RyuHayabusa78]

I had to make an extremely minor adjustment to the vertical hold knob to fix it. It's EXTREMELY touchy. Balancing the vertical hold to make the screen roll stop during these particular games while not rolling when my front end is displayed was tricky. It was super touchy. One or the other would roll when I switched between them but I finally fixed it. Thanks for the advice.

[lilshawn]

those knobs wear out really fast especially if it's been tweaked allot.

those knobs are also rated at about 200 cycles (movements) before they start getting sketchy. maybe its time for a replacement pot.

[boardjunkie]

Try cleaning the pot. They get dirty from use and age. But....here's my experience. I found that the 7000 series monitors sync better when you use seperate H/V sync. The adj was touchy with a tiny window of correct adj when I used composite sync. With seperate sync it was much happier and the correct adj "window" was closer to what I'd look for under correct operation. If you're using the Ultimarc video amp, there is the trace that can be cut to allow seperate H/V sync. Try that, modify your cabling to add the extra line.