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 Post subject: 21” Zenith 22t20 chassis *problem*
PostPosted: Apr Sat 27, 2019 10:46 pm 
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Joined: Sep Sat 12, 2015 10:13 pm
Posts: 98
Location: Knoxville, Tn
Hello all, i bought today a Zenith 21 inch console tv set from the mid 50’s. When i plugged it in at the place i bought it from, the all the tubes would glow, but there would be no picture or raster on the screen. I got it home and took the back off, and saw that the 1b3gt tube was glowing purple inside, so i replaced that tube, and when i powered it up, all the tube filiments would light up, except for the picture tube. I have tested the picture tube, and it appears to be ok. I put a multimeter on the 2 pins on the back of the tube that go to the filiment, and it reads no voltage. Whats wrong with the set? The chassis number is 22t20.


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 Post subject: Re: 21” Zenith 22t20 chassis *problem*
PostPosted: Apr Sun 28, 2019 3:12 pm 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 476
Location: New Hampshire
Should have 6.3VAC on them ( usually black & brown wires) It could be the pins
are offset & fooling you.
Another common thing was the CRT itself would get cold joints in the socket & the
filaments would go intermittent.

73 Zeno 8)
LFOD !


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 Post subject: Re: 21” Zenith 22t20 chassis *problem*
PostPosted: Apr Sun 28, 2019 3:34 pm 
Member

Joined: Sep Sat 12, 2015 10:13 pm
Posts: 98
Location: Knoxville, Tn
zeno wrote:
Should have 6.3VAC on them ( usually black & brown wires) It could be the pins
are offset & fooling you.
Another common thing was the CRT itself would get cold joints in the socket & the
filaments would go intermittent.

73 Zeno 8)
LFOD !

Actually what i meant to say is that i measured the 2 filament pins and got continuity, but i unplugged the socket from the back of the picture tube and measured the voltage on the heater pins, and didn’t have any voltage.


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 Post subject: Re: 21” Zenith 22t20 chassis *problem*
PostPosted: Apr Sun 28, 2019 6:19 pm 
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Joined: Mar Sun 01, 2009 10:27 pm
Posts: 4978
Location: Ann Arbor, MI
You could have a bad solder connection at the picture tube socket or where the wires from the socket connect to the filament wiring. It sometimes happens that people will discover a connection that was never soldered at the factory.
Some TVs have a separate filament winding on the transformer for the picture tube. Having a schematic for this set would help, but you can also trace the wiring. If you have a bad filament winding you can get a separate filament transformer to fix that.

_________________
Tom


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 Post subject: Re: 21” Zenith 22t20 chassis *problem*
PostPosted: Apr Sun 28, 2019 6:40 pm 
Member

Joined: Sep Sat 12, 2015 10:13 pm
Posts: 98
Location: Knoxville, Tn
Tom Schulz wrote:
You could have a bad solder connection at the picture tube socket or where the wires from the socket connect to the filament wiring. It sometimes happens that people will discover a connection that was never soldered at the factory.
Some TVs have a separate filament winding on the transformer for the picture tube. Having a schematic for this set would help, but you can also trace the wiring. If you have a bad filament winding you can get a separate filament transformer to fix that.


What confuses me though is i powered the set up at the house i purchased the set from, and the filament in the picture tube would glow, but as soon as i got the set home and powered it up, it wouldn’t glow anymore. Is it possible that there has been something knocked loose during transportation?


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 Post subject: Re: 21” Zenith 22t20 chassis *problem*
PostPosted: May Thu 02, 2019 7:28 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 570
Location: Belrose, NSW, Australia
Ah, that is the nature of intermittent faults that plagued this generation of technology!

When restoring old TVs I have often found soldered connections that were never properly made in the first place. Movement and temperature can dislodge them, resulting in sometimes on, sometimes off connections. You will need to chase the CRT's heater wiring back through the chassis if you have no voltage on pins 1 and 12 (either side of the key on the CRT's base).

BTW, don't get hung up on tubes and filaments lighting up. They are the least of your worries. By this time in a vintage TV's life you will rarely if ever fix a TV by changing tubes, but you WILL need to change all the paper capacitors, probably the electrolytics and even some of the mica caps. Check all resistors too while you are doing that.

You really should not power up vintage electronics like that. Doing so often causes more damage, sometimes to parts that are made of unobtainium. Google "dim bulb tester".

You are at the beginning of a long journey of learning!!

_________________
Wax, paper, bitumen, cotton, high voltages - what could possibly go wrong?


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