[wa2ise]

I did a 2nd CM7000 CECB with a modulator salvaged from another VCR. This chip was marked "3129", which I couldn't find any info on. But it had a similar 4 legged 2 channel crystal SAW TV frequency module next to it, like the other one I modified earlier. But this 3129 chip looks to have separate video and sound carrier output pins, and it uses resistors and caps to merge them together. I changed the resistors to get more signal strength. The video carrier should be about 14dB stronger than the sound carrier. That works out such that the video resistor is 1/4 that used for the sound.

This box became a channel 2 source, used a 18.432Mhz crystal to get me 3x which is very close to what channel 2's RF carrier frequency should be. Only 46KHz off. Which most TVs will fine tune into.

Noticed some audio buzz on the TV set when the bright white menu or info on-screen-display is activated. First tried reducing the video level feeding the modulator chip, but later I found that the sound carrier LC tank circuit was slightly off frequency, so I tweaked it and most of that buzz went away. Only time the buzz happens is with the menus, but not with program material, so I'll forget about it.

Just got some 28MHz fundamental crystals, and they put me at 84MHz, which turns out to be one of the frequencies CATV systems use for channel 6, and the BPC set easily tunes it, and so does a Panasonic VCR I have here also has no problem tuning it as well.