HP 34401A: strange looking caps - Page 1
Forum section: electronics / repair

author: Dachpappe
author_rank: Contributor
timestamp: March 18, 2017, 10:54:09 am
content: Finally I got myself a decent bench meter. A 34401A in good optical condition from a closed down workshop.It's an early/mid 1994 model according to the date-codes. The unit is working fine as far as I can evaluate it.Due to the mess I found in a Keithley 2000 from a friend of mine I decided to take a look at the caps.C551 and C553 (1000µF/25V/105C) are looking weird in my opinion. I've never seen this kind of bad wrap on a quality cap.Is this how a cap looks like right before it ruins the board?Take a look here:

author: Kleinstein
author_rank: Super Contributor
timestamp: March 18, 2017, 11:56:08 am
content: The two caps on the left look a little like they have positive pressure inside. However it still does not look really bad. With pressure chances are somewhat higher for the caps to leak. Since there a plenty of reports on leaking caps on K2000 it might be a good idea to chance those caps - chance are they will fail within the next 10 years.

author: 2N3055
author_rank: Super Contributor
timestamp: March 18, 2017, 12:06:10 pm
content: It might be just photo, but plastic wrap on them looks darker than that on the cap to the right, and it looks shrinked. I've seen this on Elcos that were overheating. Did you check their temperature?Also, as Kleinstein said, they look a bit puffy. I would definitely call them suspicious.

author: Seekonk
author_rank: Super Contributor
timestamp: March 18, 2017, 12:52:08 pm
content: We had a legacy product that came back for evaluation. The cap was an off purple. We still made this and the they should have been was grey. Elevated temps on caps can just dry them out and not explode. The value measured was next to nothing.

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 18, 2017, 01:59:05 pm
content: I would take the caps out and measure capacitance and ESR.

author: RayRay
author_rank: Frequent Contributor
timestamp: March 18, 2017, 02:09:49 pm
content: My opinion, if a capacitor looks physically bad or suspicious, then it should definitely be replaced!I'd recommend you get two of these:http://www.tme.eu/en/details/mal215056102e3/tht-low-imp-electrolytic-capacitors/vishay/

author: Dachpappe
author_rank: Contributor
timestamp: March 18, 2017, 10:13:43 pm
content: Thank you for your replies!As I had a decent replacement in stock (Panasonic 5000h @ 105C) I decided to change both caps.https://www.reichelt.de/Elkos-radial-105-C-1000-5000h/RAD-FC-1-000-50/3/index.html?ACTION=3&LA=446&ARTICLE=84698&GROUPID=4000&artnr=RAD+FC+1.000%2F50&SEARCH=RAD%2BFC%2B1.000%252F50I measured the capacity of the old ones and they were both at 1000µF.As my LCR-Bridge is still awaiting repair I could not check the ESR.Attached are photos of the desoldered caps. I'm not sure if they're just very badly heat shrunk of if they are actually swollen.

author: Rasz
author_rank: Super Contributor
timestamp: March 19, 2017, 10:05:38 am
content: meh, look fine to mewhats with this repairing of working equipment?

author: Armadillo
author_rank: Super Contributor
timestamp: March 19, 2017, 11:55:11 am
content: Looks like good quality caps... what a waste.

author: tecman
author_rank: Frequent Contributor
timestamp: March 19, 2017, 12:13:42 pm
content: You never can go wrong replacing old electrolyticspaul

author: Dachpappe
author_rank: Contributor
timestamp: March 19, 2017, 12:34:40 pm
content: QuoteWell, I open up every bit of used kit I buy/get used to check for risks of future failure. If I find something suspicious that's cheap and easy to replace and does not relate to any precision parts it's going to be replaced. I see it as a kind of maintenance. And 1,58€ in stocked parts that may save me from big trouble is well invested money in my opinion.