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 Post subject: Tek 442 scope problem
PostPosted: Jun Thu 13, 2019 4:36 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4497
Location: Charleston, W.Va.
A friend of mine recently obtained a Tektronix 442 dual-trace triggered sweep 35 MHz scope and has asked me to take a look at it. Here is the story:

As received, he says the scope powered up and he was able to get two stable traces. CRT appeared very bright with intensity control only about 1/4 up. But after about 15 minutes it started smoking and he immediately shut it down.

I now have this 442 scope on my workbench. Cosmetics are excellent. But I have not yet opened it up or attempted to power up. Any suggestions on how I should proceed ? I don't have the manual or service data, so any suggestions on where I can obtain same?

Thanks in advance for any help.

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 Post subject: Re: Tek 442 scope problem
PostPosted: Jun Thu 13, 2019 4:43 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 4367
Location: Sunbury, Ohio 43074
Check the power supplies, starting with B+. I'd definitely look for what was smoking before doing anything else... that could be a clue to the problem, but could also just be a symptom.

http://w140.com/tek_442_service.pdf <<service manual

You might also try getting on one of the tektronix user group forums. Just do a web search

It may be that you can fix this one without the manual, if whatever smoked is in the part of the instrument that is CAUSING the problem.

odd however that it didn't blow a fuse if a power supply simply ran away .... hopefully it'll be somewhat obvious.

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 Post subject: Re: Tek 442 scope problem
PostPosted: Jun Thu 13, 2019 5:10 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4497
Location: Charleston, W.Va.
Hi Barry,
Thanks for your fast reply and the link to the service data. As you say, I may or may not need service data depending upon what I find inside.

Yes, I plan to check the power supply circuit first. Filter caps would of course be suspect, let's hope power transformer is OK. But I agree with you, odd that a fuse would have not have blown if trouble was in power supply.

Obviously if I can identify what smoked this might point to the problem. Once I open it up I may try a brief application of power to see if it repeats itself for me. Of course while monitoring current drawn.

Later today I will open up this scope and report back here what I find.

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 Post subject: Re: Tek 442 scope problem
PostPosted: Jun Thu 13, 2019 7:30 pm 
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Joined: Feb Sun 17, 2008 11:36 pm
Posts: 2007
Location: Dayton, Ohio
A good idea when encountering a strange scope, or other electronic equipment, is to not assume someone has not installed a wrong size fuse at some time.

I hope I have not offended anyone by stating the obvious.

Charlie


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