[Zenith6S321]

I thought it might be helpful to make a thread that collected the information about my original VA62 modifications. I also want to describe the second version of the modification that adds features, provides more frequency resolution, and is easier to use.

First maybe I should describe why I did the modification in the first place. I have limited bench space and was looking for some kind of TV testing/alignment generator that would work on all TVs. The VA62 looked like it could do a lot and I got one off of Ebay for cheap. I had to clean mine up, lube the knob shafts, and get the RF oscillator working before I could use it. I got the schematics and maint manual and got it working. The VA62 was designed to allow touching up the IF and color alignment by looking at the TV picture and an oscilloscope display of the demodulated video waveform. Unfortunately it only provides the 45.75 MHz IF output. I wanted to be able to use it for both early and later TVs. If your set is mostly working you can generate an RF antenna input and use the test patterns, but if your tuner or IF is busted or way off you may not see any demodulated video. I find it easiest to inject signals starting at the CRT grid and work my way back through the video signal chain (video amps, video IF, tuner) fixing each stage until I get it working back to the antenna input. The VA62 provides the signals to drive all the stages if it has a 45.75 MHz IF.

So I decided to read the Sencore EPROM, disassembled the code, and tried to find a way to add a user adjustable early TV low IF frequency output. That's what the first modification did for the VA62. I'll describe that mod in detail next.