ArcadeVGA 5000 + Trisync = horizontal wrap (TOEI TC-AX293)

[Howdoken]

Hey guys,

Just built a new MAME PC to hook up to an Astro City and have hit a stumbling block.

Set-up

• ArcadeVGA 5000
• Win7 x64
• Toei TC-AX293 Trisync

Monitor spec: http://web.archive.org/web/20020718200115/http://www.toeitsushin.co.jp/display/tc-ax293.htm

Issue

• I get a perfect Windows desktop at 640x480 61Hz.
• At any other res the horizontal image is way off centre and wraps around the screen causing a layering effect (see image below).
• Vertically the image seems perfect.
• The image is completely stable with no rolling or other movement.
• No amount of fiddling with the H POS and H SIZE pots will fix it.
• The issue is evident on the PC boot screens, on the Windows desktop and in MAMEUI64 when set to the recommended AVGA config.

Theories

• On the chassis I spotted a pot labeled V/F HIGH, wired to an area marked V/F LOW. This pot isn't mentioned in the spec. I was wondering if it might be a manual switch to low frequency mode but I don't want to fiddle without some advice first.
• Andy from Ultimarc has suggested it might be caused by incorrect sync polarity. I'm not sure what that means or what I can do about it.

If anyone can shed any light on this issue, or give any hints or workarounds I would be extremely grateful. Thanks for reading!