Hi Guy's it's been a while.
I'm in need of a Mod for a composite input for a Pye 12G15B 12" solid state B/W portable.
I recently received an old Genie 1 computer a clone of a Dick smith System 80 or TRS80 model 1 1980's computer. Anyway I don't need sound, only video, the computer does have RF UHF36 out but it also has Composite out as well. As I have a perfectly operational Pye 12G15B 12" B/W TV I should use it. I am capable of doing the mod & can read schematics. I just need some instructions to cut what tracks & solder in the mod.

I hope someone can help!

Doug

Your in luck, I have the schematic for the 12G15B. It uses a Japanese chassis (probably Sharp) not an Australian Pye chassis so I wasn't sure if I had it. Give me a day or two and I'll scan the circuit and try and talk you through what you need to do to mod yours for video input.

Fantastic, What a champ!

Cheers
Doug

This should be a fairly easy conversion. The TV has a grounded chassis so it will be safe to work on. I thought it may have been a Sharp chassis but it's actually Korean I think, as it uses KS series transistors.

You'll need to connect the composite video input to the base of Q201 the video amplifier. It has a test point marked TP-12 on the circuit diagram which would be a good place to make a connection. You'll need to connect to TP-12 via a electrolytic capacitor with a value around 100 to 220 μF. The positive end goes to TP-12, the negative end to the video input socket that you'll need to add. You'll also need to add a 75 or 82 ohm resistor from the negative lead of the capacitor you are adding to ground to provide the correct video input impedance and also to keep the capacitor polarity correct.

To stop the noise from the tuner and IF from interfering you'll need to lift one end of L103 or L104 to disconnect the TV video source. Do not remove R109, R110, R111 or R123 as they are needed to provide bias for Q201.

If the picture ends up inverted, with poor sync you'll need an inverting buffer amp added. I'll wait and see how it goes before we try that.

You'll also need to check if the signal ground from the computer connects to mains earth. If it does, you'll need to be careful about creating an earth loop when connecting the computer and TV together. It will be pretty obvious from the picture if you do have this problem.

Pye 12G 15B Circuit Diagram

Thanks for that, I'll get stuck into the mod in a day or two. Thanks for the time taken to do the mod.

Cheers,

Doug

Glad to help. Good luck with the mod.

TV collector, thanks so much for the mod, It works. The only issue I had was de-soldering the L103 leg as it was located in a shield box & I had to disassemble half the TV to get to it. Anyway here are a couple of photo's to show the result. Since taking the photo's I've re-done the job with some shielded cable & ordered a 5 pin din plug for the computer composite input.

Looking good, I'm glad it worked out.

Nice to see what the Pye 12G-15 looks like as well. There is nothing more annoying than having a circuit diagram for something that you have no idea what it looks like.