[Zenith6S321]

I found HV service tips covering early Zenith color TVs in Tab Books No. 502 by R.L. Goodman, Zenith Color TV Service Manual chapter 5 page 68. It says:

"In all chassis using the 3AT2 HV rectifier, the picture may have all sorts of vertical, horizontal, and diagonal lines across the screen, plus elaborate rainbow effects. Also, there may be a loss of color, even though RF interference is not evident in the picture.
The cause, in this case, is an isolation resistor, located under the HV rectifier socket that has burnt or deteriorated. This is caused by a shorted HV rectifier. The most effective solution is to eliminate the resistor completely. Solder a wire across the socket terminals where the resistor was wired in, and replace the 3AT2 HV rectifier."

" ... check the filter resistor under the HV rectifier socket for arcing. DO NOT replace the resistor. Solder a lead-wire between the socket terminals where the resistor was removed."

"Improved High Voltage Rectifiers
(X and N Series Chassis)
Improvements in 3AT2 high-voltage rectifier tubes has eliminated the possibility of vertical streaking known as diodehausen. Thus, the 1.5K resistor in series with the high-voltage anode lead is not needed and has been replaced with a jumper wire to keep the outer shell of the 3AT2 socket at high-voltage potential."

I bought my used copy on Amazon. It covers from chassis 27KC20 through 14Z8C50, which includes the 25MC30 chassis.

Dave