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In circuit capacitor testers advice please.
In circuit capacitor testers advice please.
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Old 11th October 2017, 04:58 PM   #1
soul music is offline soul music  United Kingdom
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Default In circuit capacitor testers advice please.

Hi, I am an electronics novice wanting to repair a much loved 80's boombox. It was working perfectly for a few weeks after I cleaned the pots and switches, then it suddenly stopped working, no audio but tape goes round rewinds etc...lights light up, slight hum from speakers and speakers make the usual popping sound when it's switched on. Anyway I suspect one of the larger capacitors on the audio amp board may be the problem. I saw a video on YouTube demonstrating a MESR100 in circuit capacitor tester. I have a few questions about the tester before I buy one.
1 Could this tester damage other components in the boombox by testing capacitors in circuit?
2 Do all the capacitors in the circuit need discharging before testing or just the one that's being tested?
3 Can I discharge all the capacitors simply by switching boombox on with no power going to it?
4 If I do decide to buy a MESR100 tester do I go for the older model or V2 (version 2)?
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Old 11th October 2017, 06:52 PM   #2
kaputt is offline kaputt  Germany
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You can't test capacitors in circuit. You'll get a reading but it will be a reading of the capacitor plus the attached circuit.
Is there absolutely NO output? The only capacitor failure I can think of to cause that would be an open circuit output coupling cap.
As you said you cleaned all switches and pots, one of these going bad would be a pretty good explanation for no sound...
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Old 11th October 2017, 07:07 PM   #3
scottjoplin is offline scottjoplin  Wales
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Mono or stereo? What cleaner did you use?
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Old 11th October 2017, 07:23 PM   #4
soul music is offline soul music  United Kingdom
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Quote:
Originally Posted by scottjoplin View Post
Mono or stereo? What cleaner did you use?
Stereo, First Servisol Aero Klene 50 followed by Deoxit D-series.
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Old 11th October 2017, 07:23 PM   #5
Chetopia is offline Chetopia  United States
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I have personally used a Huntron Tracker before. They work just like the adds stake but are expensive for what they are. You can build one for yourself if you have access to an O'scope to use with this circuit.
How to build Oscilloscope testing module (huntron circuit) - circuit diagram
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Old 11th October 2017, 07:29 PM   #6
kaputt is offline kaputt  Germany
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Ok, back to diagnosing: is it completely silent or is there some kind of noise?
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Old 11th October 2017, 07:33 PM   #7
soul music is offline soul music  United Kingdom
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Quote:
Originally Posted by kaputt View Post
You can't test capacitors in circuit. You'll get a reading but it will be a reading of the capacitor plus the attached circuit.
Is there absolutely NO output? The only capacitor failure I can think of to cause that would be an open circuit output coupling cap.
As you said you cleaned all switches and pots, one of these going bad would be a pretty good explanation for no sound...
There is a hum from the speakers, I bought this boombox not working a few years ago on eBay with exactly the same symptoms it is having now and I had it repaired by a professional who unfortunately no longer does repairs. He replaced a cap on the audio board though I do not know if he did anything else to get it working, regarding testing caps in circuit here is the link to the YouTube video for the in circuit cap tester
YouTube
There are a lot of caps in this boombox and it really would be a time consuming job to remove them to test them.
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Old 11th October 2017, 07:35 PM   #8
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by soul music View Post
slight hum from speakers and speakers make the usual popping sound when it's switched on.
and being stereo doubt it's the amps. Tuner too? Any aux inputs?
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Old 11th October 2017, 07:36 PM   #9
kaputt is offline kaputt  Germany
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Ok. I'd say the same capacitor going bad (open circuit? short circuit?) would be a freak accident. I'd try powering the boombox from batteries for safety and short the volume pot and see what happens.
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Old 11th October 2017, 07:44 PM   #10
Chetopia is offline Chetopia  United States
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I looked up the Mesr-100 by Signstek and found a pretty good description of it's operation on Amazon. I agree it will do in-circuit testing and should not turn on any semiconductors or damage any other components during testing. Looks pretty good!
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