Adding A/V input to hot chassis SS B&W TV

[radiotvnut]

Years ago, someone gave me this fairly crusty looking GE B&W TV from 1983, which is actually a re-badged GoldStar. After all this time, I decided to play around with it and discovered that its performance was very poor (very snowy picture). By using a Sencore analyzer, I determined that the IF circuit was working, the antenna isolation network was OK, and that the fault was with the tuner. Remembering from back years ago, the tuners in these cheap Korean B&W sets were crap, and I decided I didn't want to bother with it, especially since there is no analog broadcasting left.

So, I decided to add A/V input, since DTV boxes and most DVD players have composite A/V output jacks. This set uses a video processor IC and video detection is accomplished inside the IC. So, it was just a simple matter of lifting pin 3 of the IC and running my video from the DTV box into where pin 3 originally soldered to, and I had a beautiful picture. Then, I lifted the lead going to the high side of the volume control, connected the audio output of the DTV box to the high side of the volume control, and I now had clear audio.

Then, I rigged up the A/V inputs to be where the screws were for the UHF antenna, terminated the video input jack with a 75 ohm resistor, and connected a 100uf capacitor between the center pin of the video input jack and the point on the board where pin 3 of the video IC was formerly soldered.

For the audio, I simply coupled the center pin of the audio input jack to the volume control via a 22uf capacitor.

Of course, during all of these testing procedures, I had the TV connected to an external isolation transformer. Now, I need to decide on how to isolate the input jacks. If I can find an isolation transformer that's small enough to fit in the cabinet, I may go that route. However, if that does not work out, I'll see if I can come up with some way to isolate the inputs with opto-coupler ICs.

Have any of you ever done anything like this before?