...digging deeper into the 486 'Chips' video card - it has become clearer that it video output isn't to spec.
For MS DOS text mode (assuming 720x400):
Actual (Video= 'CHIPS F65548')
Expected (based on what I could find in few monitor user manuals)
FYI - Here is what my Samsung 940N LCD is reporting - even though it is actually showing the image really well (with no scaler inbetween)
So its important to keep this in mind with any reports (including my own!) that a certain upscaler or even LCD Monitor combination 'didn't work properly' .
Its very likely the lcd screen / upscalers have a tolerance threshold that a non standard signal falls well outside of (hence the need to mess with manual adjustments). CRT screens are not as fussy.
I'm going to see if I can find any ways to adjust / correct/ clean the output kHz and hz on the video card itself or if there is a circuits that may help before I try and scale the image ( if such a thing exists) before plugging it back into a gbs or extron.
Its definaltely the video card in this 486. The default mode is out of spec refresh rates (confirmed in the video ic chip datasheet) - with a few tweaking options found in the win95 drivers.
It was originally configured to support both a directly connected digital LCD panel and an external crt. Now looking how to fix this in dos.
GBS Control via RGBs looks like it maybe the cheap winner after all.
Now that I have resolved the weird vga refresh issue in dos, I decided to re-test my scalers.
What is interesting is that my cheap aliexpress vga to hdmi converter actually performed worst than it did prior - specifically for resolution 720x400 which is typically for boot screens It resulted in a blank screen until I loaded a game. Still cropped some parts of the screen.
Gbs control was a lot easier to work with now and even worked ok when feedingVGA HV into it but will test further.
The extron 300 - worked even better than before- once I loaded a game that used 720x400, selected auto adjust in the 300 menu - it snapped the picture into the centre with correct aspect ratio and retained setting after a reboot.