Zenith 25MC33 HV Trouble

[oldtvman]

Originally Posted by compucat

I was watching my Zenith tonight for about two and a half hours with no problems and I leave the room for a moment and I hear this loud hissing sound. I check on the set to find no picture, and a slight burning smell. I pop the back off the set, open the HV cage and the flyback is hot but I can keep my finger on it. I turn the set back on and find the high voltage rectifier red plating. I have not swapped any tubes as it is late but I hope it is not the flyback. I restored this set eleven years ago, replacing all the sweep and High Voltage tubes in the process. I set the cathode current per the Sams and have never had high voltage problems with this set. Can a shorted HV rectifier cause the red plating or might I be looking at a bad flyback?

I have the same set and was lucky enough to grab an extra FBT. Check the boost rectifier diode. It sounds like time to break out the schematic and do some troubleshooting.

[compucat]

I took the second anode lead off the CRT and still no HV. At least I know the CRT is no loading it down. I do have the schematic and when I get time, I will pull the chassis and really dig into it, hopefully this weekend.