[DavGoodlin]

Having been a member for a dozen years as of today, I know this should be old hat by now. This is literally a brain trust for early color (any roundy IMHO) present company included these RCAs will test you. I started repairing curb finds when Ford was president!

I have four RCA CTC12 chassis to work on and while I am familiar with the usual task list, the original problem was an arcing vert centering control, causing CB to pop. Easy stuff, right? Not so fast, one has an oddly intermittent short that cause HV to drop out and return (blink), as HOT cathode current jumps from 190 to 270 mA, with flashes on the screen. Never had an early color RCA do this, always either the fly is good or its fried!

This is the customers one I need to fix and came with a parts chassis having a good-testing fly that has the 3A3 cap lead burned off, needing some surgery. I was suspecting an intermittent short in the flyback, so I'm ready to swap them if needed.

I ran it last night for an hour and no blinks occurred, though fly was a bit too warm and some new wax stalagmites dropped. The PS caps are still original, so sync was touchy but it had good video, sweep, color and sound. What I noticed next gave me doubts of any flyback issue. Please share any thoughts you may have on this.

After a second power-up, it began blinking again. Suspecting a shorting disc capacitor between the grid and cathode of the 6BK4, measuring voltages on both pins 1 and 5, the grid voltage drops from 375 to 280 when it blinks, cathode is steady 380v supply. So the boost supply is dropping out, allowing HV to go up by cutting off 6BK4.

Note that Horizontal drive to 6DQ5 is steady 190 vp-p, other tubes swapped were 3A3, 6BK4, 1V2 and 6DW4. The boost supply does not go too many places other than screen controls but there is a .047 maroon drop from boost to 385v supply that is suspect #1.