zenith roundie in detroit

[Robert Grant]

I have since acquired all of the tubes I may need for the set (except the 21FJP22). It is amazing how many of the chassis tubes seem to be original equipment (Zenith branded with "65-nn" codes which I suspect are date codes from the summer of 1965).

Last weekend, I removed the bottom service panel of my set for the first time to look for damaged parts.

I immediately noticed a large blue axial electrolytic cap under C1 and C2 (completely blocking my view of C1). It is a CDE cap at 160μfd, the value of each of the caps in the voltage doubler circuit. Noticing that the C2 ▲ lug has been cut from the bottom of C2, I'm assuming that the newer (circa 1980?) replacement cap replaces a defective section of C2 ▲.

The big surprise was one old-looking Mallory paper tube electrolytic that was held in place by the access panel. It had a piece of electrical tape that had been holding it to something, but had broken off sometime over the years. Its paper tube also seems to be peeling away from the cap.
Someone had combined the 80μfd and 50μfd units of it to produce a 130μfd cap, with the + end connected by long, loose wire to the cathode of the 6HE5 (vertical out) at pin 4.

At first, I had taken this to be a shoddy replacement of C5, but after a closer look, this thing really has me shaking my head. It is not in the same place as C5. In fact, C5, along with the resistor parallel to it, are still in place. C5- does not go to ground, but to part of the convergence circuit. This additional cap is between the cathode of the 6HE5 and GROUND. I don't see how the set could ever work properly with the vertical convergence given an AC path to ground. I am tempted to simply remove this strange part.

One problem I am having is that the legs on the 5317 are so short, I can't get my head under the set to see the underside and work on it, only enough clearance for a camera.

[DaveWM]

thats correct a 100uf from pin 4 6HE5 to the convergence plug for a 25v pulse.

[Electronic M]

Now for the "OH duh" moment. The pannel on the bottom was not meant to be used by sticking your head under the set. It was put there so a serviceman could tip the set on it's side and work on the under-chassis without going to the trouble of pulling the chassis out. The only things to be careful of when tiping the set on it's side are that 1.) there are atleast two screws holding the chassis in, and 2.) that you don't put too much weight on the TV's legs when tiping it on it's side lest you end up snaping one off (that will ruin your day, trust me).

I'm not familiar with Zenith roundy chassis yet so that is all the help I can presently offer.

Good luck on your restoration.

Tom C.