Zenith 19L25 Chassis Restoration - Advice?

[Phil Nelson]

Originally Posted by RitchieMars

What would be considered "normal?" As in, should I set the brightness, contrast, AGC delay, etc, to their middle positions?

Sounds sensible. If the manual has a separate procedure for setting the AGC, I'd follow that, of course.

Guess it's time for another peek with the lights out. Finding the HV leak may be frustrating, but there must be a solution. The TV worked when it left the factory, right?

Phil

[RitchieMars]

Apparently I've had a couple leaks so far, the first from the flyback itself and then the next time I was getting something around the base of the HV rectifier tube. Well, that little "tic" inside the base I had went away completely and I've heard nothing sense until today when it starts hissing out of nowhere. I had the chassis back in the cabinet when it was hissing, so I pulled it back out to have a look and so far, I've had it running about 45 minutes or so with no sign of a leak at all. But... did find something; The metal base of the HV rectifier is charged with HV. I'm not sure if it should be or not, but it is. I can take a screwdriver with a ground wire attached to it and get a vicious arch just by putting the tip within about a quarter of a inch from the metal and the bolt that holds it on that tan plastic bracket. Now if it were normal to be charged like this, that would explain the plastic bracket... but anyways, I may just need to go back and coat the rest of the flyback and seal it up a little thicker, but that tube base sure makes me wonder.

[wa2ise]

Originally Posted by RitchieMars

... did find something; The metal base of the HV rectifier is charged with HV. I'm not sure if it should be or not, but it is. I can take a screwdriver with a ground wire attached to it and get a vicious arch just by putting the tip within about a quarter of a inch from the metal and the bolt that holds it on that tan plastic bracket. Now if it were normal to be charged like this, that would explain the plastic bracket...

They probably did that to act as an electrostatic shield to the wiring in the base of the HV rectifier. Otherwise the sharp ends of terminal lugs and wiring would cause corona discharge, which might make radio frequency interference. I suppose that there is normally a metal cage to keep it out of reach.

[RitchieMars]

That's a good point, and it makes sense seeing that there's a small wire coming from inside the metal base that's soldered to the outside. There is a metal cage protecting this whole HV section, but of course it's on the topside of the chassis. I suppose that your Zenith serviceman would have known about the voltage present here, so I guess they saw no need to enclose it from the underside. I've tried to be careful around the HV section whenever I have the chassis running on it's side, but I did carelessly swing my probe past this area when I was taking some voltage readings and that's actually how I noticed the presence of HV in this area in the first place. A sudden zap from the base of the 1B3 caught me off guard, so I took note of that and later used the grounded screwdriver trick I use to discharge the CRT in order to confirm it.

I'm still going to be keeping an eye out for that HV leak, although it seems to be hiding from me at the moment. Perhaps another coat of RTV on the flyback will silence it for good. If this little nuisance will leave me be, I can get back to tracking down that contrast problem I've yet to cure as of yet.

[wa2ise]

Originally Posted by RitchieMars

I'm still going to be keeping an eye out for that HV leak, although it seems to be hiding from me at the moment. Perhaps another coat of RTV on the flyback will silence it for good.

Don't overlook putting the RTV on the sides of the HV winding. Many flybacks had a coating of thick wax or such on the outer half of the HV winding, made it look like a car tire.