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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 11th Jun 2019, 3:37 pm   #21
M0FYA Andy
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Default Re: Testing capacitors for electrical leakage

If the source of water is a result of decomposition of the paper rather than moisture ingress, why is that 'waxies' tend to degrade whereas hermetically-sealed paper 'block' capacitors stay good? Is it just that block capacitors are typically military-grade and all the materials used, including the paper, are to a superior standard?

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Old 11th Jun 2019, 3:45 pm   #22
GMB
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Default Re: Testing capacitors for electrical leakage

They don't. That fact is very strong evidence against the ingress idea.

But they are made to a higher standard so often stay good for longer. It is all about the quality of the paper. Look at books, you see the same thing. I have a valve data book that I bought new when I was a child and now the paper is almost like ash. But I have much older books by decades that are still pretty good.

I also suspect that the decomposition is auto-catalytic so once they start to go the process speeds up.
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Old 11th Jun 2019, 4:32 pm   #23
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Default Re: Testing capacitors for electrical leakage

I have a 250 volt Megger that I use to test capacitors for leakage. It works very well. the high voltage is current limited as well, so it will re-form some electrolytic caps too.
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Old 11th Jun 2019, 4:55 pm   #24
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Default Re: Testing capacitors for electrical leakage

Quote:
Originally Posted by stevehertz View Post
My modus operandi is:

1. In the case of vintage radios and TVs I change all waxies on sight. Similarly with other recognised caps that tend to be faulty such as the blue lozenge caps in Grundig sets. I cut one end of electrolytics (normally much easier than trying to desolder a multi-wire junction joint) and check using a Chinese tester for capacitance and ESR. I make good the cut wire by inserting both ends into a short 'tube' of bare tinned copper wire and soldering. So no burnt insulation, excessively heated components, swearing etc.

2. For 70s and later hifi gear I LOOK carefully for signs of leakage or bursting of all caps. Otherwise I employ recognised testing methods to point me in the direction of faulty caps. To test caps I desolder them and remove from the pcb. Again the Chinese tester is employed. I most certainly DO NOT perform blanket and unnecessary total recaps as is so popular in the US and fast making its way to a town near you.

So, two quite different MOs for me based on hands on experience of working on these two quite different types of apparatus.
It's very common in the US to "Shotgun" a repair. That is, replacing every cap in a radio or TV set, even before testing.
I preliminary test every set I'm going to restore. Many times, restorers replace every component, only to find, the thing doesn't work at all after part replacement, where it worked somewhat before.
More later, Gentlemen! Dave.
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Old 11th Jun 2019, 5:02 pm   #25
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Default Re: Testing capacitors for electrical leakage

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Originally Posted by usradcoll1 View Post
Many times, restorers replace every component, only to find, the thing doesn't work at all after part replacement, where it worked somewhat before.
More later, Gentlemen! Dave.
An all to familiar story often repeated in the forums. I guess some people have no technical knowledge at all and assume that replacing all passive components will get a piece of equipment working. All too often it doesn't.
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