How to remove a through-hole cap when you can't access the back of the board? - Page 1
Forum section: electronics / repair

author: cvanc
author_rank: Frequent Contributor
timestamp: July 10, 2019, 04:07:30 am
content: See attached generic photo, I've got a board that will besubstantialwork to access the back side that has exactly two small electrolytics I need to replace. Surely there's a better way?What are some tricks to get that old cap off the board and generate a clean location to install a replacement? I know we have the "twist" method for SMD caps - is there a clever method or two for old through-hole parts too?If I'm careful can I just wiggle and pull it out, leaving enough lead behind to grip/desolder? I've never tried that, might it work?Thanks.

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: July 10, 2019, 05:03:31 am
content: You can pull the cap off the leads, a little bit of heat might make them separate easier, but regardless you are going to be putting a lot of stress on the pads and PTH, if its an old and/or irreplaceable board I would just disassemble the device further.

author: Berni
author_rank: Super Contributor
timestamp: July 10, 2019, 05:25:51 am
content: Twisting or pulling the cap off is a bit too rough on the PCB but does work.The wiggle wiggle method is quite a bit more gentle on the board but will not leave you with a whole lot of pin left to grab on. It would proabobly work for a 2 layer board where you can heat the pad around the pin and get the heat trough the plated hole, if its single sided you will likely have problems heating it and if its a 4 6 8 etc layer board with heavy internal fills then you can be in trouble getting that short stub of a pin out at all. Its the getting the broken pin back out part that poses more risk to the PCB than the actual wiggling to beak it off.Also you won't be able to replace the capacitor properly afterwards as it wail have to be sticking out on its leads and glued down.So yeah it can certainly be done but the end result will not look very professional.

author: Psi
author_rank: Super Contributor
timestamp: July 10, 2019, 05:48:19 am
content: You can rock the cap back and forward in the direction of the legs so that the legs pull out of the cap body.Then you have the cap removed with the two legs still soldered into the pcb.Then remove the legs with the iron and solder some short wires on, or put the new cap rotated 90deg and solder its legs to the old legs.Note: i'm not saying this is a good idea, just that i have done it and it worked.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 10, 2019, 01:04:49 pm
content: Speaking of PTH, if it's not, if it's single side with unplated holes, you may well rip it out of the board, leads and all, obviously no bueno.PTH is usually strong enough to pull leads out of the capacitor though.Can do it with less stress by cutting the capacitor itself in half. Use an old pair of diagonal cutters that you won't mind denting (or causing accelerated rusting on). Cut it about at the waist. This should cut through the thickest part of the leads, which are upset or coined to retain them in the rubber seal, and below the roll of foil and electrolyte-soaked paper (or through it, which is okay too). Cut off the rubber plug (or melt/burn it off?) and clean up the leads as pigtails for your repair.Tim

author: cvanc
author_rank: Frequent Contributor
timestamp: July 10, 2019, 01:15:26 pm
content: Quote from: T3sl4co1l on July 10, 2019, 01:04:49 pmYeah, I was thinking along this line - behead the little bastards. I'll give it a try (and I had not thought about the corrosive aftereffects, will use some unloved cutters).And yes, it's double-sided PTH and a decent quality board. Hope it stands up to my onslaught

author: cvanc
author_rank: Frequent Contributor
timestamp: July 10, 2019, 01:51:03 pm
content: Annnnd... done.Photos to show the process. Cut the top half off, wiggled/pulled the lower half (rubber bung) off the intact leads, desoldered with some good wick to get nice clean holes, and soldered in the new part a bit up in the air (which actually allows me to lean the replacement away from a hot transistor that probably started this whole situation anyway LOL).Thanks!