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Electrolytic capacitor question
factory:
I've seen too many capacitors from the 1980s & early 1990s with failed seals, that leak corrosive & conductive electrolyte over boards, for me to leave them in place. Sometimes it's not obvious there is capacitor pee until the cap is removed.
Some PSU failures caused by this, then go on to cause major damage elsewhere.
Brands that I've seen leak include; Philips, Panasonic, Nichicon, Rubycon, Chemicon, and Sprague.
Last week we had a failure of critical equipment at work, with strange fault codes & random shutdown, a Matsushita/Panasonic cap was responsible, the capacitor pee had even found it's way through a filled via to the other side of the PCB, the equipment in question dates from 1994.
Going too small in physical size for replacements can lead to SMPS caps, with high ripple running hotter than the old ones, in extreme cases they vent, yes we had this happen at work when bean-counters choose the replacements.
Of course there are different cap technologies, that can be smaller & have lower ESR, but they come with their own failure modes.
David
Xena E:
Just a Cautionary note.
Smaller cased electrolytic caps for any given ratings can just mean that further replacement intervals may be reduced as they dry out quicker; manufacturing has gotten so good that life specs are as close to reality as posted values, and very often I have found new 10uF alelcaps claiming 10% tolerance and measuring just north of 9uF! Sneaky barstards.
*Lower ESR is not always a desirable feature*
Shotgun replacement of capacitors en masse, is a real good way of turning the job into scrap if you're not very careful.
Xena.
Messtechniker:
--- Quote from: Zero999 on February 02, 2024, 11:31:54 pm ---Smaller isn't always better. Smaller capacitors might have a higher ESR and also won't be able to dissipate as much heat generated by the ripple current, as well as larger ones.
--- End quote ---
To get around this, I sometimes replace one old large (mostly dead) capacitor by two smaller capacitors in parallel. Same total capacitance of course. This helps with ESR and heat dissipation.
factory:
--- Quote from: Xena E on February 04, 2024, 10:29:27 am ---Just a Cautionary note.
Smaller cased electrolytic caps for any given ratings can just mean that further replacement intervals may be reduced as they dry out quicker; manufacturing has gotten so good that life specs are as close to reality as posted values, and very often I have found new 10uF alelcaps claiming 10% tolerance and measuring just north of 9uF! Sneaky barstards.
*Lower ESR is not always a desirable feature*
Shotgun replacement of capacitors en masse, is a real good way of turning the job into scrap if you're not very careful.
Xena.
--- End quote ---
Yes every type of capacitor has different pros & cons.
And there is risk in leaving the original caps in place too, of course they might be of a type that is OK too.
If the OP has no experience of repairing/replacing parts, then it would be wise to practice on something of low/no value, with similar double sided or multilayer boards, before working on this scope.
David
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