Hi All,

My father a while ago game me his old Panasonic portable black and white TV. I have plans on cleaning it up and using it again, but I would like to add a composite video input and audio so I don't have to use the original tuner (though it still works but I currently don't have a modulator). Can anyone provide me with a PDF of a schematic so I can attempt to add it in while I work on acquiring a VHF modulator.

Thanks.

A bit non-trivial on that model, easy enough to get something working, not so easy to get it working properly.

Can you assemble a kit? If so:

https://vintage-radio.com.au/home.asp?f=6&th=214&offset=3

Silicon Chip mag published this and you can buy the PCB and some parts from them.

Thanks for your reply,

I do have experience building kits so I will give it a go. Can the Silicon Chip kit also transmit in colour because it would also like to use it on some other sets that are colour.

But I would also like the option to just go in directly. I have tried to put in the signal of a portable DVD player into the IF part of the TV at the terminals that are on the tuner and it was able to process the signal but it was distorted. Would disconnecting the tuner fix this, does the RF AGC trimmer on the back of the set need to be adjusted because it is overloading the circuit or do I need to inject it directly into the video part of the set?

Thanks.

Yes that modulator does colour just fine.

You need to go in at the video detector generally. Sometimes you can get away with just AC coupling the video to the cathode of the diode and disabling the IF. But this will rarely be ideal. Levels, bias need to be right to get good sync.

If your set has a high 'level contrast control it's easier. Contrast via the AGC won't work here.

I did these conversions for years, I built a business doing it, sold mod kits to NEC, Philips and Mitsubishi. But for vintage TVs a good modulator is what you want. So I designed one of those too!

Thanks for your reply,

I will have to try to experiment with it, In the mean time I am going to invest in one of the Silicone Chip modulators just so I have a second option just in case it fails.

Where can I go to find a schematic or even better, a service manual on it so I can find the appropriate injection point on the set?

Thanks.

You're in luck!

I have the service manual & I'll scan it for you.

National TR602A Circuit Diagram
National TR602A Service Manual

Thanks for your reply,

Thank you very much, I have been looking for a schematic or service manual ever since I first got the set, Apart from this modification, the set just needs a good clean and polish because it has been sitting in a unused caravan for I believe the past 10+ years. I use to have a Jaycar VHF-UHF modulator but it kicked the bucket recently.

Thanks

Documents uploaded to Post 6.