Zenith 25MC33 HV Trouble

[compucat]

I pulled the chassis today. After partially dismantling the high voltage cage, I found the trouble. A hole had burned into the hv rectifier filament wire. I found another wire in a box of Zenith roundie parts and installed it. I also replaced the 1.5k resistor with a 1k since it is all I had. The high voltage came right back up with no arcing. I put the set back together and checked the high voltage. It was a 30kv presumably because of the resistor replacement. I turned it down to 25kv as recommended in the Sams. Now for a new problem. The horizontal hold will not lock. I suspect the afc diodes because it will operate throughout the range of the horizontal hold control but at center it will not lock in. I have been having trouble up to this point where the horizontal hold would drift especially after being on for a half hour or more and would have to be set further toward the end of the control range to bring it in. I don’t have any diodes to replace them with so I will have to wait until I can order them. I did replace the 6U10 horizontal osc, afc and discharge tube to no affect. I am just glad the flyback did not fail.

[Penthode]

There may be more problems lurking around the flyback transformer. Generally a pulse winding on the fly back feeds the phase detector and if it is open, you will lose lock.

Can you post the schematic focussed on the horizontal afc?

[compucat]

I got it fixed. It turned out it was a dirty tube socket causing the horizontal hold not to lock. I touched up the convergence and a few other adjustments and now it is back as great as ever. These old sets will keep you guessing sometimes.