flagging on rgb screen

[Hurleyautoaudio]

Any help is appreciated. I got some inexpensive ntsc to rgb convertor boards
to convert and send dvd movie to gps screen on a customer's car. All is well
with system-except a flagging on upper right hand corner of screen. It looks
kinda like the corner of a page turned down. No other source can tell me what
i need to do to get rid of this.

-poor sycn
-voltage mismatch
-bad freq refresh

thanks

gar