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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 15th Jan 2019, 7:45 pm   #1
Martin G7MRV
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Default What sort of capacitor is this?

Im working on repairing a Clansman PRC344 UHF manpack, and have found a capacitor on the 6V regulator module to be dead short. This is connected across the input direct from the battery to ground (via a varistor I think).

It is a black cuboid device, about half an inch square by a quarter thick, made by ITT. Its marked with a + and 22uF which suggests to me its some form of electrolytic, an early tantalum perhaps?

I've removed it from the board and it tests dead short out of circuit. It was secured to the board with some form of rubbery varnish, so taking it off mean destroying it!

There's a photo of it on the module PCB here on my blog https://g7mrv.blogspot.com/

I'd just like to know if these have a 'reputation', as it looks like Plessey used a lot of them in this radio!
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Old 15th Jan 2019, 8:18 pm   #2
Martin G7MRV
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Default Re: What sort of capacitor is this?

Markings are -

ITT 22u +35v

The + is by one lead, and that lead emerges from red epoxy.


I would have put this in an edit but I missed the 30min limit by seconds!
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Old 15th Jan 2019, 9:13 pm   #3
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Default Re: What sort of capacitor is this?

ITT 1980 general catalogue has a miniature moulded solid tantalum type TAH which might be similar. Can't tell from your picture if it is axial or radial but spec is the same.
Could be 10% or 20% tolerance and surge rating is 46 volts at 85C.
Case size of this type is 12.1 x 9.6 x 3.9mm.
Construction is "box and end fill" acording to a web search on the TAH type.
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Old 15th Jan 2019, 10:43 pm   #4
Martin G7MRV
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Default Re: What sort of capacitor is this?

Cheers George,

Tantalum as expected, but a little bigger then.

I've replaced it with a modern sub-miniature electrolytic. Sadly, on powering the radio up I was met with the sound and smell of another component dying! Looks to be the 12v regulator this time!
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Old 15th Jan 2019, 11:15 pm   #5
Martin G7MRV
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Default Re: What sort of capacitor is this?

Well, turns out that its the same capacitor in the 12v regulator thats failed! Unfortunately, its burnt up the inductor in series with the supply, so as well as replacing the capacitor ive now to re-wind a 13t ferrite bead!

Are these caps known to be a problem?
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Old 15th Jan 2019, 11:20 pm   #6
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Default Re: What sort of capacitor is this?

Quote:
Are these caps known to be a problem?
Well - they are now!
Never met that particular type in the flesh but have had a tantalum go in a SMPS recently and have had any number of bead types fail s/c (spattered capacitor) in the past.
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Old 15th Jan 2019, 11:32 pm   #7
Martin G7MRV
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Default Re: What sort of capacitor is this?

Well thats two blown in this one radio! Both in identical modules (the 12v, 6v, and 3v regulators are all the same LM100H just adjusted as needed). The 3v seems to be working, but ive a mind to pull it and replace the cap as a precaution!

Im hoping its just these in the regulators, since they have raw 24v supply from the battery on them (which can be anything up to 28v).

Ive not looked into the 80v supply module yet, but i'd hazard a guess theres one in there as well!

Oh well, radio bought untested, I always knew I was taking a gamble...
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