UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Converting RF TV to direct Video and Audio

Argus25 · 24th Nov 2019, 10:05 am

It is actually very easy to couple into the video circuitry of a TV, to inject a composite video signal, and couple into the audio circuitry to inject an audio signal to turn the TV into a "video monitor".

Sure you can get your video and audio signals, feed them to an RF modulator and then feed that to the TV as an RF signal at the antenna input, as has been suggested, but the quality loss is pretty severe. Maybe you can tolerate that.

In fact , back in the mid 1970s' when TV's were cheap, but video monitors with composite video inputs and line audio inputs were expensive, many home computer enthusiasts modified the TV sets to receive video inputs to save themselves a truckload of cash.Even one of the first video arcade games, Atari's Pong 1972, had inside it no more than an off the shelf Hitachi TV set , modified to have video & audio inputs.

Its fairly easy on the audio side, you can usually just inject the audio at the top leg of the volume control normally and disconnect or disable the TV's audio detector/IF so you don't get hiss mixed in or disconnect the top leg from the feed in the TV set.

In the video circuit (of the particular set) you need to look at the output of the video IF & detector and work out the polarity of the video signal there and where the sync is taken off so you can inject your video signal (typically 1V pp terminated) into the correct part of the circuit with the correct polarity and so the H & V sync are stripped off downstream of that point in the circuit.

So clearly, as many questions like yours dictate, you will require the schematic of your set unless you are prepared to trace it out (which I have done many times when the schematic is not available)

To help with the many iterations that are possible with this solution, Don Lancaster wrote an article about it in Byte magazine 1975. It is reprinted in this computer manual, you will have to scroll to page 234 of the page numbers on the pdf not the document page numbering. The article is called "Television Interface":

https://deramp.com/downloads/process...s%20Manual.pdf

Hugo.

24th Nov 2019, 10:05 am	#5
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Converting RF TV to direct Video and Audio It is actually very easy to couple into the video circuitry of a TV, to inject a composite video signal, and couple into the audio circuitry to inject an audio signal to turn the TV into a "video monitor". Sure you can get your video and audio signals, feed them to an RF modulator and then feed that to the TV as an RF signal at the antenna input, as has been suggested, but the quality loss is pretty severe. Maybe you can tolerate that. In fact , back in the mid 1970s' when TV's were cheap, but video monitors with composite video inputs and line audio inputs were expensive, many home computer enthusiasts modified the TV sets to receive video inputs to save themselves a truckload of cash.Even one of the first video arcade games, Atari's Pong 1972, had inside it no more than an off the shelf Hitachi TV set , modified to have video & audio inputs. Its fairly easy on the audio side, you can usually just inject the audio at the top leg of the volume control normally and disconnect or disable the TV's audio detector/IF so you don't get hiss mixed in or disconnect the top leg from the feed in the TV set. In the video circuit (of the particular set) you need to look at the output of the video IF & detector and work out the polarity of the video signal there and where the sync is taken off so you can inject your video signal (typically 1V pp terminated) into the correct part of the circuit with the correct polarity and so the H & V sync are stripped off downstream of that point in the circuit. So clearly, as many questions like yours dictate, you will require the schematic of your set unless you are prepared to trace it out (which I have done many times when the schematic is not available) To help with the many iterations that are possible with this solution, Don Lancaster wrote an article about it in Byte magazine 1975. It is reprinted in this computer manual, you will have to scroll to page 234 of the page numbers on the pdf not the document page numbering. The article is called "Television Interface": https://deramp.com/downloads/process...s%20Manual.pdf Hugo.