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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Nov Mon 03, 2014 7:47 pm 
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Saw this in a set I recapped Saturday. The thing is that I've seen this probably 4-5 times before with these bumblebee caps. When they go.. I imagine they go literally with a big "Bang!"

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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Nov Mon 03, 2014 7:53 pm 
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Here's another one.

This one is a game of which came first, the botched repair or the burned out resistor? The 830 mmfd micamold capacitor is supposed to be a 870 ohm 1 watt resistor between the + side of a 200uf cap & B-. Hey, the numbers look close enough. Resistance, capacitance, same difference??

Image

But the more visible problem is that 140 ohm 3 watt resistor has been cooked well-done.


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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Nov Tue 04, 2014 12:54 am 
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That IS a wirewound resistor! Micamold made them, between 1935-55 or so. If it measures OK, leave it alone; the violet dot is a bit faded in the photograph. Looks like it's in a Zenith, and that's no surprise, as they used them quite a bit.

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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Nov Tue 04, 2014 1:03 am 
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Yeah, that REALLY confused me on a '42 Zenith that I was fixing up. Wirewound resistors in molded domino packages, totally threw me off. Never seen them in any other radio, ever.


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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Nov Tue 04, 2014 3:44 am 
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Never seen them in anything other than a Zenith. Their 1940's era car radios had them. Okay, one possible exception: Those 1946-48 Ford/Mercury Rotomatic radios; if it has provision for the foot pedal it's a Zenith. If it doesn't, it's a Detrola. Exactly the same radio, except for Detrola logo on the caps and other components, and of course the lack of a foot pedal connector. The Zenith has a domino resistor in the power supply, between the first and second electrolytic. I can only assume the Detrola version has the same thing.

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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Nov Tue 04, 2014 4:09 am 
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Here are some pictures of Majestic model 20 clock radio that I fixed for a friend a few years ago. It had some melted tar issues.

Some signs of melted tar when I pulled the chassis from the cabinet:

Image

Bottom of the chassis:

Image

The surprise hiding inside. I finally got the bottom cover off with a heat gun:

Image

It turns out that the filter capacitor bank had overheated. All of the tar like potting material around the capacitors had leaked out into the bottom of the chassis. This radio actually sounded pretty good when I was done, but it wasn't simple to rebuild.


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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Nov Tue 04, 2014 3:42 pm 
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It helps to think of the tar as an automated anti-rust protective covering material.


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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Nov Tue 04, 2014 6:33 pm 
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That micamold is a resistor?! How about that. I had no idea. Mine measures open. Is it odd that its value doesn't match the schematic [830 v 870]?


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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Nov Tue 04, 2014 6:45 pm 
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Quote:
That micamold is a resistor?!

yep. i just replaced a few in radios that were 150 ohm 1-2 watt cathode resistors.

steve


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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Nov Fri 07, 2014 12:25 am 
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Besides Zenith, I have seen them in a few other makes. Emerson and Stewart-Warner used them, and there are a few in my Farnsworth-made BC-312.

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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Sep Tue 14, 2021 7:47 pm 
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jkoebel, did you ever write the article?

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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Sep Tue 14, 2021 8:01 pm 
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Had to look through my archives, looks like this was in the March 2015 issue of Nuts & Volts Magazine

chaz's picture of the mouse nest, Rocco53's picture of the juice can coil shield, and I did use your picture of the AK 55 lava flow it looks like. (I also used two of my own photos, a Simplex Model P which had both missing and extra parts, and a 1931 Westinghouse grandfather clock which caught on fire.)

phinegan wrote:
jkoebel, did you ever write the article?


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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Sep Wed 15, 2021 2:07 pm 
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I take it that the article isn't available online. Correct?

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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Sep Fri 17, 2021 9:19 pm 
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Not a radio, but the worst for me the PC computers I was working on back in the bad electrolytic formula capacitor era. Very common to open the case, and see popped top capacitor cans with leaking goo, and even the unraveled innards and cans shot off and scattered about. Service philosophy was to replace the motherboards and power supplies in the field, and I must have replaced thousands.

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 Post subject: Re: Pictures of radios that have had a problem or meltdown
PostPosted: Sep Thu 23, 2021 4:45 am 
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phinegan wrote:
I take it that the article isn't available online. Correct?


Apparently not. Only two articles from March 2015 on their website, unrelated to this subject.

https://www.nutsvolts.com/blog/archives

Edit: The above is a blog on their website, not the magazine archives. If you're a subscriber, you can view old issues online. There's a sort of preview which has the table of contents for each online issue. Here's the March, 2015 issue: https://nutsvolts.texterity.com/nutsvol ... 3?pg=6#pg6

But... There have been no new issues for 2021, and even the blog stopped in March of this year. I sent an email yesterday inquiring if the magazine is still being published, no reponse yet.

As to JW Koebel's "meltdown" article, it's not listed in the March, 2015 table of contents. I also looked at earlier and later issues, while I did see there had been some articles he wrote on radio or hifi restorations and other topics, however I couldn't locate this one.

-Ed

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