ADVCFG Display Blank Between 201 and 240 lines

[Kook]

Maybe one of you video gurus can help me. I've been playing around with advcfg.exe a long time, trying to get the perfect video configuration. My setup is as follows:

Trident Blade T64 driving a Wells Gardner 25" display (through a JPAC card). It's a standard resolution arcade monitor in a Mortal Kombat II cab. I boot into Windows 98SE and load blade15.exe. Thus Windows looks good at 640X480. Normally, I run MAMEWAH from here and launch my MAME games using ADVMAME. It works great. But now I want to set it up for perfect video using advcfg. So here's my problem. From Windows, I open a DOS full screen and load BLADETSR. Everything looks good. Then I run advcfg and specify valid settings (5-90 / 15.72 / 51-63). I get to the ADVCFG screen where you are supposed to adjust and center the screen, and everything still looks fine. If I adjust the vertical size of the screen using k and Shift+K, the screen goes completely blank for any settings between 201 lines and 240 lines. 200 lines are fine. 241 lines look fine. However, what I want is 240 lines (to match most games out there). It doesn't matter what pclock, hsync, or vsync settings I use in advcfg... the centering screen always blanks out for settings between 201 lines and 240 lines.

What the heck is going on???

Kook