[drh4683]

bob,

you lost your color sync. I remember seeing corrosion inside that set. Try rocking the color tubes around, color should pop back in. If not, either a defective 3.58osc.,reactance, or AFC tube is causing trouble. Should that fail to cure it, there are probably cracked solder joints on the PCB. The only thing I can think is that when you removed the 6GF7, the PCB pulled up and either cracked a solder joint or caused a tube pin to lose good contact. Be very cautious when pulling a tube out of a set with PCB (printed circuit board). If I remember correct, its just one huge PCB with no support on it at all, the entire board would bend and flex when a tube was pulled.
Flip the set on its top and pull the bottom cover off and inspect the tube socket solder joints very carefully, if they are cracked it will be a very fine circular crack around the pin of the socket. You need a sharp eye to catch it, so be patient. If you want, rotate the suspect tubes in their sockets while looking at the solder joints, it will help you pin down the loose cracked one as you will see very slight movement or opening of the cracked spot. Its no zenith thats for sure.

Good luck-Doug