No love on the TV front

I had hoped that adding Composite Video to my little black and white Panasonic television would be a piece of cake, and in fact it looked like it would be a piece of cake. But it is not. It is not a piece of cake. It is not a piece of any kind of pastry.

After a lot of time playing around and poking and prodding and probing signals here and there, I have successfully gotten composite video to appear on the screen, sort of, by putting an ordinary 1V P-P composite video signal into the video driver transistor’s base (pin 3 of IC12), and grounding the video coax to the input of the horizontal sync separator (pin 1 of IC12), which is just not at all how I expected it to work. But “work” is not really the right term, because it’s obviously not really right; the video looks weird and very washed out, and no amount of futzing with controls gets it looking acceptable.

The problem here is twofold: One, I don’t really grok analog TV circuits yet, and two, this TV is a hybrid between discrete logic and ICs. I think the circuit would be a lot simpler for me to understand if it were fully discrete, and I think it would be a lot easier to add composite input if it were either fully discrete or more fully IC based. But since it’s a weird in-between thing, some of the functions are separated into ICs in such a way that I don’t really “get” it. So, I think this will just be a TV I’m willing to junk so I can learn about how to drive a CRT in general, and not something for any specific project ideas.

That said, if you’re curious here’s the schematics and the IC details.

Schematics
Schematics
IC Descriptions
IC Descriptions

Composite Video

Sweet, I just found this YouTube video about adding composite input to a television. It looks much simpler than I anticipated.

I also just got the schematics for my set, so I’m in business.

Adventures in NTSC

While I was in Seattle last weekend I popped into a few thrift shops looking for vintage electronics goodies to pull apart. I found this little 5” television from 1984, for a whopping $2.50:

Panasonic TR-5110T

I know it looks like it’s color, but it’s actually black and white—I connected a Commodore 64 through a horribly kludged together RF demodulator just to test it out, since we don’t have analog television broadcasting any more.

What I’d like to do first is open it up and add a composite video input, so maybe I can drive it with a Raspberry Pi or something. It has no video input other than antenna right now. I’ve never really hacked video equipment before, so it’ll be fun new territory for me. Don Lancaster’s classic book “TV Typewriter Cookbook” (PDF, 13.5MB) has a treasure trove of information about how to interface with an analog television, so it’s going to be my bible for TV experiments.

I do need to get my hands on a service manual for the TV. I found a place that sells them online (for $17, almost 7 times what I paid for the TV itself!), so maybe I’ll just have to do that.