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 Post subject: Zenith porthole 1B3 HV Resistor Question
PostPosted: Sep Thu 28, 2017 3:48 am 
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Joined: Jan Sat 16, 2016 10:03 pm
Posts: 316
Hello everybody

One of my Zeniths Porthole CRT picture started to display an extremely dim/foggy raster out of no-where. I pulled the chassis (23G22) and checked out the high voltage section and found the high voltage filter resistor under the 1B3 socket connected in-between the door knob cap and the CRT anode (R123) (470K) looked rather burnt up. So I removed it and it checked out at 52K. I've never experienced a resistor dropping almost 10 times in value. Has anybody else experienced this before or anybody interested in educating me a little.

Thank you very much

Curt


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 Post subject: Re: Zenith porthole 1B3 HV Resistor Question
PostPosted: Sep Thu 28, 2017 3:55 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 31179
Location: Maryland 20709, USA
clsoca wrote:
So I removed it and it checked out at 52K.
52K what?

Is that leakage resistance or capacitance?

- Leigh

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 Post subject: Re: Zenith porthole 1B3 HV Resistor Question
PostPosted: Sep Thu 28, 2017 4:04 am 
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Joined: Jan Sat 16, 2016 10:03 pm
Posts: 316
Its a resistor rated at 470K that test at 52K


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 Post subject: Re: Zenith porthole 1B3 HV Resistor Question
PostPosted: Sep Thu 28, 2017 4:07 pm 
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Joined: Nov Thu 11, 2010 6:03 pm
Posts: 629
Location: Pewaukee, WI
HV can arc, arcing causes carbon tracking, carbon tracking causes KV rated plastic insulators to have K ohm resistances.... I'm not surprised by that change in value.


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 Post subject: Re: Zenith porthole 1B3 HV Resistor Question
PostPosted: Sep Thu 28, 2017 4:42 pm 
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Joined: Jan Sat 16, 2016 10:03 pm
Posts: 316
Electronic Memory wrote:
HV can arc, arcing causes carbon tracking, carbon tracking causes KV rated plastic insulators to have K ohm resistances.... I'm not surprised by that change in value.


Thank you for your response. I understand now how the ohm value dropped dramatically. There is very little on the internet about this subject.


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 Post subject: Re: Zenith porthole 1B3 HV Resistor Question
PostPosted: Sep Thu 28, 2017 6:33 pm 
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Joined: Apr Thu 14, 2016 8:25 pm
Posts: 278
Location: pensacola fl
Yes resistors do go down in value. Carbon resistors have done it. Sylvania had a hybrid set with 2 47k 2W resistors in the chroma section that would go way down resulting in transistors litterally burning up. there are other examples as well so check those carbon resistors from the day for this condition.


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