In Car TV (CRT, yes CRT) Help.

[derekjay]

Background

I am currently working on a project to restore a Toyota Soarer MZ12 from 1985. It was the first car to have an in dash TV (obviously CRT). Here is a page detailing the TV and Driver system.

Problem

The CRT appears to have given up. When I had the CRT plugged in, I could vaguely see the Multivision display, but it appeared ghostly, and looked like the CRT tube was not happy.

Solution

Replace the CRT with an LCD. But to do this, I need an LCD of the right size, LCD driver board, and something to convert what was being sent to the CRT into something that the LCD driver board can use.

Conundrum/Question

Here is what I know so far: http://yojiko.com/yo/ji/ko/pw/EMV_to_LCD-Part_1 and Here are the circuit boards: http://mz12gt.com/?p=293

The last point of the driver box are two chips. AN5315and AN5352.

The AN5315 takes a composite video signal and converts it into "color difference" signals. B-Y, G-Y, R-Y and Y(Y is luminance).

The AN5352 takes a teletext character signal in R, G, B and adds it to the B-Y, G-Y, R-Y and Y output of the AN5315. Here is what I see when I run the teletext character signal through a Jamma board into a monitor. There is something.

What I want to know is. How do I convert the B-Y, G-Y, R-Y and Y or RGBS to something I can see on a monitor?

Here are some things I have tried:

• I have tried running the B-Y and R-Y and Y signals into the Jamma card, via YPbPr connections, but get junk, I think because the Y is missing the sync. Here is a video
• I have tried adding the sync to the Y channel using the circuit described here: http://www.raphnet.net/electronique/sync-on-green/sync-on-green_en.php but instead of adding the sync to the green adding it to the Y channel. This did not work, either because, I used the wrong sync (the TV driver board seems to offer 4 syncs, sync for the teletext signal, a combined sync (I think), H-Sync and V-Sync (I think)), I used what I thought was the combined sync, or the circuit doesn't work for adding sync to Y, or my prototype building skills suck. Does anyone know if this should work?
• I have tried to use the RGB signal that feeds into the neck of the CRT tube as input to the Jamma board. There seems to be a circuit, that adds the Y channel back into the R-Y, G-Y, B-Y channels, with adjustment, just before it is sent to the tube. Does anyone know if this would be a suitable place to source RGB for an RGBS input to the Jamma card? (it doesn't seem to work) Can anyone supply me with a diagram of a circuit that would add Y back to the R-Y, G-Y, B-Y channels? The one on the board before the CRT seems overly complicated as it has adjustments for brightness, which I don't need
• I have tried scoping the RGBS. http://yojiko.com/yo/ji/ko/pG/EMV_to_LCD-Part_2
  
  Sync
  
  Colour and Sync
  
• I have tried feeding the RGBS signal that was going into the AN5352 into the Jamma board. Which occasionally shows a frame grab, but won't lock on.
  Here is a video I have also tried using a variety of sync cleaning methods: http://yojiko.com/yo/ji/ko/pY/EMV_to_LCD-Part_3_More_Hardware none of which seemed to work. And in fact were worse than not using it. The RGBS signal would occasionally show a frame grab, but running through any of the sync cleaners I tried, I got nothing.

TLDR;

Does anyone have any experience with hacking TV circuitry especially colour difference circuitry? What is the simplest way to get the output of a AN5315 chip to produce something I can convert to VGA to power an LCD? Alternatively what is the simplest way to get the input to an AN5352 to convert to VGA to power an LCD?

Here is a video of an actual working In Car TV from a MZ12 Soarer:

Research shows that the AN5352 chip was used in the Commodore Amiga 1080 monitor Manual here The block diagram indicates to me that RGB inputs to the AN5352 work completely independently of the R-Y, B-Y, G-Y inputs that it takes from the AN5315 chip in my board. Which means I can just tap those inputs.

The upscalers/converters I have tried are GBS8200 and GBS8219. I have been able to get signals out of the GBS8200 but never managed to get anything out of the GBS8219 (despite it costing more and being advertised to handle a wider range of inputs).

[amyk]

What horizontal/vertical frequency does it run at? Is it interlaced?  If it's close enough to VGA timings (and often, even if it's not) multisync VGA scalers will have no trouble with the signal.

The AN5352 datasheet has an application circuit at the end that shows it driving a CRT through some circuitry; it might be easiest to take the analog RGB from where it drives the tube (dividing it down to VGA levels) and sync from the horizontal/vertical deflection circuits.

[Scrts]

You would need a video encoder, which would have analog inputs. These encoders usually have YUV output (you may find some RGB ones - check the manufacturers like ADI or TI), so then you need to change the YUV back to RGB and supply this directly to the LCD panel. This can be done by FPGA easily.

[derekjay]

Thanks for the ideas.

I can definitely scope the RGBs signal coming out of the computer in the boot. So far I have tried:
GBS8200
GBS8219
Additionally I have used LM1881 sync cleaners to clean the sync signal.
None of these have produced a usable signal.

Additionally, it is getting quite expensive trying this stuff, so I would like to know if there is a sure fire solution to the problem. Or even a way I can diagnose what is going on.

Do people have recommendations on RGB to VGA converters?

[amyk]

Additionally, it is getting quite expensive trying this stuff, so I would like to know if there is a sure fire solution to the problem. Or even a way I can diagnose what is going on.

You have a scope, make measurements of the signal timing that I wrote above. What you can do next depends on how close to VGA it is/what the montor you'll be using can accept. The conversion circuit could be as simple as a few passives and transistors, or you might need a full framebuffer-type scan converter.

[derekjay]

You have a scope, make measurements of the signal timing that I wrote above. What you can do next depends on how close to VGA it is/what the montor you'll be using can accept. The conversion circuit could be as simple as a few passives and transistors, or you might need a full framebuffer-type scan converter.

Ok. Will do.