Shortly before the first portableMotorola DynaTAC "brick" cellular telephone filled the palm of a Wall street yuppie, the original Sharp Sidekick was illuminating the camping trips of working class families. No I'm not having an episode of temporal displacement, or writing an episode of the Twilight Zone. The original Sharp Sidekick was a portable 5" B&W TV, not a cell phone with a slide out screen.
My Grandfather bought a used 1981 vintage Sharp Sidekick model # 3S-62 at a yard sale back in the mid nineties. He gave it to me and it's been sitting on a shelf in a closet for many years. I decided to bring this relic out of hibernation and make it more useful in today's world.
This TV, of course, has an analog tuner and can only be fed an RF signal through the VHF and UHF antenna terminals. This isn't of much use since the transition from analog to digital broadcast in 2009. One way that this TV can be used to watch broadcast, or cable is by installing a 300-to-75 ohm matching transformer, then connect a digital converter or cable box via 75 ohm coaxial cable. Another option is to use an RF modulator to convert composite or S-video signals to RF.
I wanted to have a set of composite (RCA) input jacks built in to the TV for convenience. That's what I set out to do, and with some deduction and a little trial and error I was successful. While I was at it I also upgraded the built in speaker for better sound. Please read on to learn how I did it.
It seemed to me that I should be able to find the part of the circuit where the demodulated video signal is fed to the tube driving circuitry. I started by locating the demodulation section, which is housed inside the large metal shielding box. I traced the wire bundles from the horizontal PC board that the demodulator is attached to over to the vertical tube driver board. I determined that a grey three wire shielded cable was the demodulated audio and took note of this for a later step. I guessed that the demodulated video signal feed would be in the larger bundle connected toward the top back edge of the tube driver board.