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old electronic devices electrolytic capacitors
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Siwastaja:

--- Quote from: Wallace Gasiewicz on November 27, 2020, 01:45:32 pm ---I have had non electrolytic caps explode (more like a small firecracker) once in an old DC to AC converter, that was in an old radio.
Don't really know what the root problem was since the radio was damaged by someone using the wrong power cord, wrong pinout, had to rebuild the converter.
Made a mess in the garage.

--- End quote ---

Might have been the infamous RIFA capacitors. They are plastic film capacitors* made with completely botched manufacturing process so they fail catastrophically after some 10-30 years of storage or operation. It's an interesting story how an assumed "good" brand product can be a total disaster.

*) proper modern replacements being self-healing, very long life, very reliable
Alex Eisenhut:
Well if it helps, my Dad's Grundig radio from 1959 was not powered for 10+ years, the other night I finally powered it up.

Just plugged it in and turned it on.

No Variac, no reforming, just full power.

It took 10 seconds to warm up and pulled in a local radio station nice and clear. Oh, and it's a selenium rectifier for the B+, so no slow warm up there.

Just adding to the controversy.
madires:
I think the idea of a preventive maintenance for electrolytics is about keeping the aluminum oxide layer stable, i.e. the isolation layer. Doesn't matter much for low voltage applications, but might for higher voltages. The manufactures tell you about a max. shelf live to be on the safe side. Based on their specs I'd guess powering on a device with high voltage electrolytics every 6 months could help to keep the oxide layer in shape. Anyway, I have a bunch of old electrolytics from power supplies for audio power amps laying around and they are still in excellent condition, despite not being used for decades, while most of the old blue Philips electrolytics became junk.
Siwastaja:

--- Quote from: Alex Eisenhut on November 27, 2020, 03:20:50 pm ---Well if it helps, my Dad's Grundig radio from 1959 was not powered for 10+ years, the other night I finally powered it up.

Just plugged it in and turned it on.

No Variac, no reforming, just full power.

It took 10 seconds to warm up and pulled in a local radio station nice and clear. Oh, and it's a selenium rectifier for the B+, so no slow warm up there.

Just adding to the controversy.

--- End quote ---

IMHO, there's nothing weird about this.

People expect old electrolytic caps to explode, but this isn't typical, I think it's more about hearing the stories than actually experiencing problems. I have never seen it happen, personally. I always just plug in the old stuff.

Reforming increase the chances of success, maybe from 90% to 95%, but old devices Just Working despite no reforming at all is still the expected result.

In audio equipment, the problem with bad electrolytics may be increased hum due to increased ESR and decreased capacitance, and reforming may not help significantly, replacement is often necessary.
Gyro:

--- Quote from: Siwastaja on November 27, 2020, 02:50:48 pm ---Might have been the infamous RIFA capacitors. They are plastic film capacitors* made with completely botched manufacturing process so they fail catastrophically after some 10-30 years of storage or operation. It's an interesting story how an assumed "good" brand product can be a total disaster.

*) proper modern replacements being self-healing, very long life, very reliable

--- End quote ---

They're Metallised Paper actually. It gives them a higher dV/dt capability than plastic film types (that's why they are used), they're actually really good capacitors when they're not exploding!

Still self-healing (metallisation) but unfortunately, being paper, they are a lot more prone to failure on package cracking and moisture ingress.
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