Max 2 LCD Conversion - So Close

[gthlm]

But not quite there...

I bought a GBS8219 converter (a very good piece of kit btw, bit pricey though...). I found some basic schematics for the ultimax 2 console that I managed to use to hook up the converter.

I can get a perfect image for the graphics. No problems there.

However, I'm not having so much luck with the text screen. I've got a lovely clear image, BUT, it's like image has been cut in two vertically and the two sides swapped round. The picture is NOT wrapped, adjusting the horizontal position to the extremes just results in a cropped image with blank/corrupted image to either side. I've been in touch with tech support and the factory for the converter but we've been unable so far to solve this problem.

If anyone could help me out with the specifics of the video output from the CRT controller card it might help get to the bottom of the problem!

Thanks, Gregor

[fasto]

Text screen uses CGA for horizontal and vertical timings, and is monochrome although CGA defines 4 or 16 colors. If I recall correctly, it's 15.7 kHz for horizontal and 60Hz for vertical. My notes are elsewhere. Check if the scan converter goes this low in frequency. Your symptoms seem to me like the scan converter is locking into the 2nd harmonic - ie, 31.4 Khz which is within the VGA range that these scan converters are usually used for.

Graphics screen uses EGA for video display, as far as horizontal & vertical timings, though it's monochrome and EGA defines 16 or 64 colors. Of course, you've already got this one sorted.

[gthlm]

Thanks for the reply. The converter has a horizontal frequency range of 12-40khz and has the signal locked at 16.23khz x 60hz vertical.

I have only a very basic understanding of how the video signal is interpreted at the crt board side in this kind of system, and have no idea whatsoever of what variations in the input signal cause what symptoms on the output image!

I'm not having much luck finding people who DO have a good understanding of this stuff either, locally or on the internet, so I appreciate your input

If the horizontal frequency of the video source is 15.7khz and the converter is miscalculating it as 16.23, would that cause the problem, or is it more likely that the source is actually 16.23khz due to imprecision/aging of the components or whatever?

I believe there are means to override the auto detection on the converter, but I would need to ask tech. support for the parameters. It's not one of those cheap arcade game converters off of ebay

Thanks, Gregor

[bloke]

Gregor, I'm sure I've seen something about a switch on the CRT controller that changes frequency. I'll check in the morning for you.

[bloke]

Gregor, There was a switch on the older CRT controller 1 that toggled between 50Hz and 60Hz. It was on SW1 number 5.
I'm still trying to find out if CRT controller 2 has an equivalent...

[gthlm]

Gregor, There was a switch on the older CRT controller 1 that toggled between 50Hz and 60Hz. It was on SW1 number 5.
I'm still trying to find out if CRT controller 2 has an equivalent...

Well, mine has a second jumper that I've never worked out the purpose of...

Appreciate your help, Gregor