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 Post subject: TO 7000-1 Transistor Measles
PostPosted: Jan Sat 26, 2013 12:36 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 4766
Location: Melbourne, Florida
My thirteen dollar 7000-1 Transoceanic stopped working last night. I traced the problem to one of the transistors in the IF strip, then substituted with the ubiquitous 2N2222A and the set came right up.

When I examined the transistor I took out I noticed some bright places around the leads. Examination under magnification revealed lots of tiny bright spots all over the insulator between the leads and the case. Cleaning these deposits off brought the transistor back to life and made the radio happy.

This phenonenom is the transistor version of the infamous silver mica disease and was found back during the space program. Apparently it was not yet fixed when the transistors for this TO were made. Now I can wait for the next infection.

RRM


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 Post subject: Re: TO 7000-1 Transistor Measles
PostPosted: Jan Sat 26, 2013 1:57 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 6838
Location: Indianapolis, IN
Interesting & thanks for posting... What did you use to remove the conductive "spots" ?

John


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 Post subject: Re: TO 7000-1 Transistor Measles
PostPosted: Jan Sat 26, 2013 2:05 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 4766
Location: Melbourne, Florida
The tip of an exacto knife blade.

RRM


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 Post subject: Re: TO 7000-1 Transistor Measles
PostPosted: Jan Sat 26, 2013 6:04 am 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 5594
Location: Sunnyvale CA
Retired Radio Man wrote:
My thirteen dollar 7000-1 Transoceanic stopped working last night. I traced the problem to one of the transistors in the IF strip, then substituted with the ubiquitous 2N2222A and the set came right up.

When I examined the transistor I took out I noticed some bright places around the leads. Examination under magnification revealed lots of tiny bright spots all over the insulator between the leads and the case. Cleaning these deposits off brought the transistor back to life and made the radio happy.

This phenonenom is the transistor version of the infamous silver mica disease and was found back during the space program. Apparently it was not yet fixed when the transistors for this TO were made. Now I can wait for the next infection.

RRM


That's very interesting! Hadn't seen that one before.

Brett


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 Post subject: Re: TO 7000-1 Transistor Measles
PostPosted: Jan Sat 26, 2013 11:19 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10267
Location: Beaver Falls, PA. USA
Sounds like the "tin whiskers" problem.

_________________
Tim KA3JRT


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 Post subject: Re: TO 7000-1 Transistor Measles
PostPosted: Jan Sun 27, 2013 2:31 am 
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Joined: Sep Fri 07, 2007 2:21 am
Posts: 1709
Location: Brunswick, ME 04011 (USA)
...now, this makes me wonder if the transistors in the (a few years later) D7000 series were also subject to this phenomenon...something to watch out for, for sure...


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