Capacitor getting hot - Page 1
Forum section: electronics / beginners

author: ironsniper1
author_rank: Regular Contributor
timestamp: October 13, 2024, 10:20:59 pm
content: Hey all i am trying to fix a psu for an old vcr and have replaced the caps as they needed it, however something is causing the cap in the high voltage section to get so hot that it blows its gets out, i have already replaced it however i do not have any more caps, i have checked the diodes around the cap and the other caps around it and so far havent found anything, if anyone has any ideas let me know, the area in question is the high voltage section in the picture marked with the blue square

author: AndersJ
author_rank: Frequent Contributor
timestamp: October 13, 2024, 10:36:23 pm
content: Perhaps you reversed the polarity?

author: ironsniper1
author_rank: Regular Contributor
timestamp: October 13, 2024, 10:48:45 pm
content: nope i checked and double checked, its also mmarked on the board which side is negative

author: Kim Christensen
author_rank: Super Contributor
timestamp: October 13, 2024, 10:52:37 pm
content: Have you checked the bridge rectifier which is under the 33K resistor?

author: ironsniper1
author_rank: Regular Contributor
timestamp: October 13, 2024, 10:55:11 pm
content: i have not but i can

author: ironsniper1
author_rank: Regular Contributor
timestamp: October 13, 2024, 11:18:50 pm
content: it seems to be test good but i will need to replace it as one of the legs came off during removal

author: amyk
author_rank: Super Contributor
timestamp: October 14, 2024, 03:41:50 am
content: Is this the primary reservoir cap? Either overvoltage or reverse polarity could do it.Are you sure you replaced it with one of the right voltage? Note that the board markings can sometimes be incorrect or misleading so it's best to trace out the circuit to confirm. If you can find a schematic to work from, that would be even more helpful.

author: ironsniper1
author_rank: Regular Contributor
timestamp: October 14, 2024, 04:40:20 am
content: i made sure i put back in the same way as the old one its only a 330uf 25v cap, old one was 330uf 18v

author: tooki
author_rank: Super Contributor
timestamp: October 14, 2024, 07:04:12 am
content: Quote from: ironsniper1 on October 13, 2024, 10:48:45 pmEvery once in a while, a board has the markings wrong. So it’s good to check the schematic (if available), any photos you took before working on it, or reverse-engineering the circuit to figure out what polarity it needs to be.

author: Poroit
author_rank: Frequent Contributor
timestamp: October 14, 2024, 08:16:11 am
content: Gday Ironsniper1,1.Was that 330ufd 18V cap blown when you first opened the PSU?2.That physically large capacitor in the HV area is most likely your Primary Reservoir cap. Have you tested it as it does not seem to have been removed from the PCB(dusty)?3.What instrument are you using to check caps?

author: PGPG
author_rank: Frequent Contributor
timestamp: October 14, 2024, 09:08:12 am
content: Quote from: ironsniper1 on October 13, 2024, 10:20:59 pmDid you replaced caps with approximate ones?Capacitors working in 100kHz circuit need to have low ESR at these frequencies while capacitors working at 100 or 120Hz need not it. Because of these you can buy cheap capacitors for working with main frequency and more expensive destined to work with high frequency.If you used capacitor not having low ESR than few times higher power is released in capacitor and its temperature rise instead of for example designed 30°C can be 90°C.

author: Xena E
author_rank: Frequent Contributor
timestamp: October 14, 2024, 09:29:54 am
content: Quote from: ironsniper1 on October 14, 2024, 04:40:20 amAre you sure it wasn't an 18uf 330 voltEdit:(The capacitor in the middle of your blue square is an 82 uf one)

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 14, 2024, 03:58:26 pm
content: Old, even (especially?) NOS capacitors can have a high leakage current. This can cause enough heating to destroy the capacitor though overheating. The remedy is to put on a high value series resistor to limit the current and then let it sit for a few days. Look into electrolytic capacitor reforming for more details.

author: golden_labels
author_rank: Super Contributor
timestamp: October 14, 2024, 05:47:12 pm
content: I bet Xena is right. But if not, please clarify a few things. Most importantly: mark the capacitor in your picture. A photo of the other side of the board would help too.Also, how did you measure the temperature? If by touching with your finger: cases of aluminium electrolytic capacitors are not isolated. zap zap

author: floobydust
author_rank: Super Contributor
timestamp: October 14, 2024, 08:27:12 pm
content: OP's Panasonic VCR power supply "Ref. No. 1000 Series", Assy. No. VEPS0181 there are repair/recap kits oneBaythe five caps look kinda cheap though.There's a 330uF 16V part in the mix.I would confirm making no new mistakes (caps backwards, solder bridges etc.) when recapping the board.Otherwise, the board might not be regulating properly (with no load too) and that rail goes way over voltage so the cap heats up.