Author Topic: Resistor on a post in CRT monitor?  (Read 401 times)

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Offline gmcTopic starter

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Resistor on a post in CRT monitor?
« on: May 27, 2024, 03:31:21 pm »
I'm busy trying to repair a old 12" CRT from the early 80's - Yes, I'm  aware of the electrical dangers  ;)

One of the components is a 56R resistor which is now reading 100R. Looking at the schematic it's a 56R RN1/4 which from what I can gather is a 0.25W Metal Film Resistor.  Resistor looks a bit worse for wear and has overheated.

That's all good and easily replaceable. One thing that I've noticed is that there are a few resistors around the HV side that have one leg soldered to a post which I've not seen before.

Guessing it's to keep it off the PCB for cooling? But why one leg and why mount it to a post? (Or is the post also some sort of heat sink?)

Was this a standard for the CRT's in the 80's?

 

Offline johansen

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Re: Resistor on a post in CRT monitor?
« Reply #1 on: May 27, 2024, 04:38:31 pm »
Usually 2 posts were used to keep the heat away from the board
 

Offline jonpaul

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Re: Resistor on a post in CRT monitor?
« Reply #2 on: May 27, 2024, 04:56:26 pm »
post keeps HV arc to PCB surface eg dust.

Very common.

Use carbon comp resistor rated for the HV

Jon
Jean-Paul  the Internet Dinosaur
 
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Offline gmcTopic starter

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Re: Resistor on a post in CRT monitor?
« Reply #3 on: May 27, 2024, 06:08:33 pm »
Thanks for the info. Will source the correct resistor replacement.
 

Offline inse

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Re: Resistor on a post in CRT monitor?
« Reply #4 on: May 28, 2024, 03:57:50 am »
You can see the windings, this isn’t a carbon composition resistor but a metal film type.
« Last Edit: May 28, 2024, 04:52:41 am by inse »
 
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Offline CaptDon

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Re: Resistor on a post in CRT monitor?
« Reply #5 on: May 28, 2024, 04:31:22 pm »
I absolutely agree that it is metal film!!! Carbon Comp replacement is a huge mistake seeing how the metal film burned up. I would also recommend the flameproof version FP which the original resistor probably was. Looks like the O.E.M. expected a possible failure mode of this part and could be part of the reason for the post mounting.
Collector and repairer of vintage and not so vintage electronic gadgets and test equipment. What's the difference between a pizza and a musician? A pizza can feed a family of four!! Classically trained guitarist. Sound engineer.
 
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