Zenith Roundie HV Question - Help Please

[julianburke]

When I was doing Zenith TV's (others too) and you are not getting raster, the first thing is to pull the damper tube out slightly and if it arcs on the socket it is good and conducting. If it didn't arc you would replace the damper tube for starters to go on to the next step. (or fixed it at this point) If damper is good, next pull the cap off the the HV rectifier, stick an insulated Xcelite nutdriver or other in the cage and touch it to the cap from flyback. (don't ground it-any arc or corona is enough test) If you get arc there, you have a bad 3AT2 (or 3A3 in other sets) rectifier. Usually the HV rectifier filament opens and then will "lay" on the plate internally creating a short and keep HV from building so disconnecting the cap will prove this point. The focus 1V2 or 2AV2 rarely goes bad and if it does, will not cause loss of raster. If you still can't get it to work, measure resistance between the two caps of the HO tube and the HV rectifier (power off of course) and the resistance through the flyback should be about 75 ohms. If near zero or infinity, fly is bad. Julian

[compucat]

Thanks for the useful information Julian. I did get the HV to work if I pulled the CRT socket. With the CRT connected, I get no HV although I can hear the Horizontal oscillator squealing and I was getting pink and purple glow and flashes inside the CRT neck. I have sent the tube to Hawkeye for rebuilding. In fact he should be working on it this week. The cabinet is still at the refinisher's. I will be so glad to get this put back together. In the meantime, I'm doing a lot of parts and chassis cleaning. I can't wait to watch Star Trek on it.

[julianburke]

You have an easy one here. Your CRT is broken or cracked and has aired. When a CRT has gone down to air, it will arc internally all over the guns or half down to air will produce a strong blue or pink glow internally. When down to air, tube is "shorted" and will build HV and arc internally but no raster and I have seen some tubes that are internally shorted (perhaps not down to air-your case) and by removing the CRT socket will build HV again. Remember, any arcing around the guns indicates your tube has "aired". When first you see this condition, turn set OFF immediately as it is very hard on the sweep circuit (short across flyback) and will ruin the HO tube and/or flyback if left on. Julian

[compucat]

I'm sure my tube has not completely gone to air because the filaments did not burn out. I suspect that the tube was the cause of most of the problems. The chassis seems to be in good shape. I just love the way these Zeniths were built to last. I'm hoping to get many years of service out of this set. I plan to connect it to a digital set top box/DVD recorder combo.

[julianburke]

Contrary to popular belief, Zenith did build a quality set BUT that's not the main reason they built them like that. They were expensive and labor intensive to manufacture because they were too cheap to upgrade their facilities! They did too little to late to upgrade and this is the main reason they went out of business sooner than they should have. Zenith always shouted "QUALITY AND HAND BUILT" but no one else was doing this in the competitive market. Julian

[compucat]

I'm glad Zenith was slow to upgrade. Tubes and PC boards are not a good combination. Restorers of RCA roundies have to contend with broken connections, loose grounds, brittle boards and crumbling tube sockets. The heat just tears them up. PC boards are fine for solid state although I think heat generating components like large wattage resistors and power transistors should be chassis mounted. When it comes to tubes, handwired is the only way I'll go.

[Carmine]

Originally Posted by julianburke

Contrary to popular belief, Zenith did build a quality set BUT that's not the main reason they built them like that. They were expensive and labor intensive to manufacture because they were too cheap to upgrade their facilities! They did too little to late to upgrade and this is the main reason they went out of business sooner than they should have. Zenith always shouted "QUALITY AND HAND BUILT" but no one else was doing this in the competitive market. Julian

This was mentioned before, and I don't know if I buy it. Seems to me that Zenith didn't skimp on the R&D money, afterall they gave us a lot of great radio innovations, ever-smaller & better hearing aids, and in the TV world:

Wireless Remote Control
Phone-o-vison (ok, that didn't catch on)
Chromacolor CRTs
Stereo TV (I think)

...didn't they also have a "better" color demod circuit?

And when they finally went to PC boards, the chassis were still tanks.

They were also the number 2 set maker, so being as how they must have been pretty profitable, I'm sure they could have gone to PC boards and made even more cash by cheapening the sets and laying-off a lot of solderers!

[ChrisW6ATV]

Originally Posted by Carmine

Stereo TV (I think)

Yes, Zenith invented the U.S. (BTSC) analog stereo-TV audio format.

Zenith also invented the digital TV system now in use in the USA, Korea, and other countries. When the commission was formed to study and approve high-definition TV, three other companies came up with analog proposals but Zenith invented a digital format. Zenith's signal was so superior, the commission (ATSC) told everyone to give up on analog entirely.