Troubleshooting 15khz on Sony KX1901 RGB monitor

[txgraeme]

Hello forum, I'm working on a cabinet build involving an old Sony KX1901 Profeel monitor and a computer running GA-2015 which will output through an AMD HD 6310. I am using the monitor's 34 pin inputs on the 1v analog settings and have got the system running well and at correct sync rates but having some issues I am hoping someone can help me identify. I am struggling with how to define my problems, as my guesses at search terms have not been productive.

Here is a video of Mame running one of the included Roms:


And here is LXDE:


I have identified 4 issues:
1) Colors fade after initial appearance on screen.
2) Mame runs in the lower left corner, but desktop and system menus are correctly centered otherwise.
3) Scaling seems wrong/too small.
4) Overscan is not setup correctly.

My assumption is that the color issues are related to monitor hardware.  Something like output not being above threshold voltage. To clarify, the monitor works well as a television (ntsc) and I even prefer watching this unit to my newer hardware.  Great color, clarity, and blackness. It is from 1982, so I realize a cap kit might be in order, but if so then likely only for the rgb input card rather than main board.

I double-checked my cable and couldn't find a problem, but that also might be a source of trouble.  Unfortunately since it's all custom I can't swap to test it.

When I use an LCD monitor on vga out @ 31khz the output looks spot-on, but still not centered.

I can only imagine how much time this community has put into this amazing suite of software and drivers, so first off thank you for that.  I would appreciate any tips or helpful links as I continue my troubleshooting efforts.

[txgraeme]

I have an update on the work from first post regarding sending RGB to Sony KX-1901.  So after putting it aside for a while, I have recently made some progress.  I was able to output native 15khz signal from Raspberry Pi 2 w/VGA666, which allowed me to troubleshoot which problems come from TV set and which are from the Radeon side.  The pixel clock on RPi was giving me some problems, but there is enough sync ranges that overlap so you can get it to work.



I have been able to figure out that my software is responsible for the centering and scaling problems I was having, so should be able to resolve those eventually.  There are still some issues with the display, in that the colors are fading from screen when I use the RGB inputs.  Since the VGA output works well on other devices, then I believe the problem is now coming from the home-built cable I am using.  It's made from a IDC 34 pin floppy ribbon cable spliced to BNC breakout connectors.  I have tried 2 different VGA to 5-BNC (RGBHV) adapters and both give similar results. 



I'm trying to troubleshoot the cable, as that's the likely source of problems and also easiest to eliminate from suspicion.  My understanding of the Sony manual is that it expects a 75ohm connector and a 1-v peak-to-peak RGB signal, and my VGA is currently sending a 0.7v RGB signal down a cable with 7.5ohm (as measured on multimeter).  Would appreciate if anyone has a tip on what steps to take or a good guide on the basics of these custom cables.

[txgraeme]

Further along in my experiments now, and have been successful in generating 240p and 480i signals. I have also found that the tv unit will sync with NTSC and PAL frequencies, just need to be careful with sync pulse timings.

But have also found that the TV unit is not intended for analog RGB, even though it accepts an analog signal in place of TTL. I guess this is the difference between KX-1901/2501 and later KX-1901a/2501a units. The display converts the 1v p-p color signal and uses that to determine if color is full on/off, which yields a total of about 8 colors. Or in terms of SMB, it looks like this:



I believe there is a possibility of intercepting and injecting midtones via RGsB later on board, so am still experimenting with options. Here are boards that combine video & teletext before sending to neck:



You can see the 34 pin connector at bottom, and RGB out at top that goes directly to neck board transisors.



Reverse view of board with some of the 34 pin connector numbers and labels.

[txgraeme]

I have tried injecting vga level RGB at the board output and have confirmed it works well, but needs a higher voltage and DC offset. Looks pretty good so far, the 240p RGB really brings out the color and artwork.  I should be able to build an amp to get to right level, or may grab an off the shelf version if any are recommended.

Here is current screenshot from SMW.

[Tym01]

Hi! Could you please reattach the pictures of your mod to get proper RGB on the sony profeel monitor?
I have a KX20PS1 and the same problem occurs with colors on an analog RGB source, i was thinking about trying connecting the RGB inputs directly to the neck board RGB inputs, i would really love to see how you managed to have good RGB! You can also send me the pictures if you still have them, here is my email: azzamtym at gmail.com

Thanks a lot!!

Regards

Tymour