Mica capacitor leakage - Page 1
Forum section: electronics / repair

author: abhi1981
author_rank: Regular Contributor
timestamp: May 05, 2025, 06:15:20 pm
content: HiThere is waxy residue below these mica capacitors.Are they leaking? Please advise.Testing in capacitance mode shows no reading.They are 22pf 500v mica capacitors.

author: Haenk
author_rank: Super Contributor
timestamp: May 05, 2025, 06:22:33 pm
content: No, these are often wax dipped. Looks perfectly fine to me.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: May 05, 2025, 06:24:50 pm
content: These are NOT Mica capacitors, Should they be Y rated filter capacitors?G Edmonds

author: abhi1981
author_rank: Regular Contributor
timestamp: May 05, 2025, 06:26:42 pm
content: Thanks for the prompt reply.But why is the multimeter showing no reading in capacitance mode? I'm using a KAIWEETS KM601S.Is there a different method to test them?

author: George Edmonds
author_rank: Frequent Contributor
timestamp: May 05, 2025, 06:31:52 pm
content: Your photographs appear to show a hole blown in the side, if so they will show no capacitance.G Edmonds

author: abhi1981
author_rank: Regular Contributor
timestamp: May 05, 2025, 06:32:11 pm
content: Quote from: George Edmonds on May 05, 2025, 06:24:50 pmThey are mica capacitors. I checked the part no. in the service manual.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 05, 2025, 06:35:09 pm
content: Quote from: George Edmonds on May 05, 2025, 06:31:52 pmThat's what I think. One of them was totally covered in wax, so much so that the reading was not visible. The board is installed vertically, so the wax has flowed downwards.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: May 05, 2025, 06:46:58 pm
content: If you have a manual can you attach a copy?G Edmonds

author: abhi1981
author_rank: Regular Contributor
timestamp: May 05, 2025, 06:56:56 pm
content: Please find attached the required manual pages. Couldn't post the full manual due to large size.The capacitor are C809, 811, 815

author: factory
author_rank: Super Contributor
timestamp: May 05, 2025, 07:19:12 pm
content: Quote from: abhi1981 on May 05, 2025, 06:56:56 pmThose capacitors are shown as 22pF of the diagram & parts list andnot 220pF, 22pF is probably too low a value for the DMM you are using.David

author: abhi1981
author_rank: Regular Contributor
timestamp: May 05, 2025, 07:26:32 pm
content: Oops!! My bad. I wrote the printed value instead of the actual value.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 05, 2025, 07:28:42 pm
content: How to test such low values?

author: factory
author_rank: Super Contributor
timestamp: May 05, 2025, 07:49:44 pm
content: Others will be able to recommend a modern LCR meter, mine is more of an antique.David

author: George Edmonds
author_rank: Frequent Contributor
timestamp: May 05, 2025, 08:05:58 pm
content: HiThe KM601S is claimed to mesure down to 1pF, yes pigs do fly. That is jf you are still alive after using it with the charger plugged in.G Edmonds

author: aeg
author_rank: Regular Contributor
timestamp: May 06, 2025, 06:18:32 am
content: Quote from: abhi1981 on May 05, 2025, 07:26:32 pmThe last digit of capacitor codes is an exponent - so 220 printed on the part means 22*10^0 = 22*1 = 22pF

author: Haenk
author_rank: Super Contributor
timestamp: May 06, 2025, 07:59:49 am
content: Stop it, George. Every single one of your posts is containing nonsense.The multimeter claims +-4% error (plus digits) on capacity measurement in 10nf range, aka 10000pf. I.e. the error range is 800pf, that's 40 times the actual value. Also add some for the leads.So the multimeter simply isn't suited to measure this. (1pf display resolution is just utter chinese marketing BS, it has nothing to do with measurement resolution)Don't believe me? Read the manual, it's stated in the specs.Also, the Micas rarely fail, I'd consider them the least likely part in your device to be defective, by far. There is no possibly-turning-bad chemistry involved, it's actual metal coated rock (so to speak).

author: George Edmonds
author_rank: Frequent Contributor
timestamp: May 06, 2025, 08:38:53 am
content: CrapOn the 9.999nF range it has a claimed resolution of 0.001nF which is 1pF.G Edmonds

author: Gyro
author_rank: Super Contributor
timestamp: May 06, 2025, 09:15:11 am
content: Quote from: George Edmonds on May 06, 2025, 08:38:53 amClaimedresolution, not measurement. Big difference. No DMM with flying leads is going to be able to measure 22pF. Lead movement, touching the leads, noise, etc. will completely swamp 22pF of capacitance. Add to that the meter's specified accuracy, as Haenk mentions any there is no chance of a sensible measurement.

author: Haenk
author_rank: Super Contributor
timestamp: May 06, 2025, 10:21:08 am
content: Quote from: Gyro on May 06, 2025, 09:15:11 amI have a bag of precision 1% 100pf Micas - using my LCR meter(*), they measure spot on 100pf (when plugged in directly). Just for fun, I tried to measure with (Probemaster, aka "quality") leads, without even touching the cable, that added 15-20pf.(* specs +-0,5% in 20nF range; but likely better, as tested with precision Mica and resistors)

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 06, 2025, 01:07:28 pm
content: I can't recall about mica capacitors made problems. Those on a photo as for me look like made that way from manufacturer. I mean they are probably ok.

author: Dave Wise
author_rank: Regular Contributor
timestamp: May 06, 2025, 02:56:14 pm
content: I agree with Vovk_Z. It looks to me like the manufacturer's dipping process misses the space between the leads, so they cover that area by hand with a different material. These caps are almost certainly okay.Mica caps have unusual failure modes. Sometimes they leak, but often they begin to randomly change capacitance or increase dissipation factor, when contact to individual electrode sheets weakens.