[Zenith6S321]

I bolted the chassis into the cabinet and tipped it on its side so that I could get at the underside of the chassis and see the picture. I started through the color AFC alignment procedure but I could not get a zero beat pattern with the reactance tube input grounded. I put my Heathkit frequency counter on the color oscillator and found it running at 3.581391 MHz, pic attached. After scoping a few points I found a bad connection on the reactance transformer supply input. I guess it had been cut at some time and poorly soldered back. This is probably the reason I could occasionally get the color to lock 30+ years ago. With that fixed and some fiddling with the fine tuning I got the color to lock, but I still could not get a zero beat pattern when adjusting the reactance transformer. I could reduce the number of out-of-sync color bars, but there was not enough range to reach zero beat. I put the frequency counter back on the color oscillator and found that when it locked the frequency counter read 3.579445 MHz, pic attached. With the reactance transformer adjusted for the minimum number of color bars, the counter read 3.579653 MHz. So the reactance transformer would let me adjust the frequency down, but not down far enough to reach zero beat. I had one old crystal and five NOS I just bought, so I tried them and got these frequencies:

RCA crystal dated 11/56 3.579653
Crystek #1 3.579651
Crystek #2 3.579644
Crystek #3 3.579625
Crystek #4 3.579647
Crystek #5 3.579632
COYSON dated 3/75 3.579614

I put the Crystek #5 crystal back in, since it was about the middle of the set of frequencies, and verified it read the same after putting it back in. Then I added a 1pF ceramic cap to across the crystal and saw it lower the frequency. I ended up with 3pF across the crystal to get a frequency lower than the locked frequency with the reactance transformer adjusted for its lowest frequency. Now I could adjust the frequency up to get a zero beat of the color bars with the reactance input grounded. I did the rest of the color AFC alignment and ended up with color that remained locked with acceptable fine tuning.