Advice on how to remove large through hole binding posts - Page 1
Forum section: electronics / repair

author: Esquared
author_rank: Contributor
timestamp: April 20, 2022, 08:49:54 pm
content: I have an old BK Precision 1760 triple output supply that two of the binding posts have been smashed offto use the supply you have to hold the test leads against the remaining stubs which is far from ideal; this is a friend's equipment that got damaged in a move. I got replacement binding posts and opened the supply up but I ended up needing to back out of the repair the other day as I was beginning to lift a pad on a PCB. I didn't take a picture but I drew up what I'm dealing with. The problem is the whole assembly is captive to the front panel which makes it difficult to work on. I have good soldering and desoldering equipment (FX-888D and FR-301) but I was having trouble removing the solder off the binding posts in the PCB no matter what I did there was still solder deep in the large plated hole for the binding post. It just didn't want to pull out no matter how many times I tried adding new solder and sucking it off again, wick couldn't pick it up. Not sure if there is a way to fix it but it would be nice if I could. The worst part is that since it is a triple supply each of these PCBs has three terminals to be removed and one post is broken on the "A" supply and one post is broken on the "B" supply. So basically to replace two posts I need to remove 6...

author: BrokenYugo
author_rank: Super Contributor
timestamp: April 20, 2022, 08:56:47 pm
content: Maybe a low melt alloy? Never used one myself but people seem to like it for difficult desoldering jobs.Usually I say more heat more quickly, but if you're lifting pads you've probably already pushed that to the limits of the gear.EDIT: I have found that with wick sometimes if you really flood the area with flux it helps with the capillary action to pull the solder from the other end of the hole. If you don't have any liquid/paste electronics soldering flux you're really missing out.

author: Esquared
author_rank: Contributor
timestamp: April 20, 2022, 09:13:26 pm
content: Yeah it is tricky. I didn't completely lift the pad but I saw a small corner begin to come up. It is obviously a big power trace so it is hard to do anything with it anyways. I tried preheating from a far distance with a hot air station set to a low-ish temp just to not be working a cold board. I had covered the area in flux so no problems there. I just think it is a dicky design. Quite honestly I was surprised to see it on a PCB I would've figured it would have a wire going directly to it.

author: BrokenYugo
author_rank: Super Contributor
timestamp: April 20, 2022, 09:36:49 pm
content: Also, pictures of everything may be helpful. How big is the pin and how much is sticking through?

author: Esquared
author_rank: Contributor
timestamp: April 20, 2022, 09:43:52 pm
content: The pin is roughly 2.9mm in diameter and about 2mm is sticking out the back side of the PCB, I was looking at getting a special tip for the FR-301 to get some better access. I won't have a chance to get pictures either till tomorrow or Friday.

author: BrokenYugo
author_rank: Super Contributor
timestamp: April 20, 2022, 10:34:25 pm
content: Pin flat on the end? Since the connector is already written off I'm thinking preheat everything a bit with air and then drive all the heat you can into the pin alone with the 888 and a heavy tip with with a suitable flat on it, crank the tip temp to get as much stored energy as possible. It'll hopefully heat up enough to melt all the solder eventually (5-10 seconds?), which can then be sucked or blown out.Can you expand on the 301 tip trouble? Kind of goes without saying, but if you can't get on the pin/pad good with clearance for solder to flow through, that'd probably be your problem.

author: edpalmer42
author_rank: Super Contributor
timestamp: April 20, 2022, 11:51:09 pm
content: I suspect that your soldering iron isn't up to the task. This sounds like a job for a soldering gun rated for at least 100W. 200W wouldn't be out of line. When your iron doesn't have enough power it takes a long time to heat up the joint and the glue holding the trace onto the board gets cooked to death. A bigger iron is able to heat the joint faster and completely melt the solder, get the job done, and be gone before the glue is destroyed.Ed

author: Esquared
author_rank: Contributor
timestamp: April 21, 2022, 01:05:24 am
content: I agree with ed I think I need some bigger artillery to get it done. As far as the tip goes I was looking into getting one of the extended tips so I could get in tighter to get a better seal+thermal transfer around the perimeter of the pin.

author: c64
author_rank: Frequent Contributor
timestamp: April 21, 2022, 06:28:52 am
content: Solder bath.Hint: it doesn't need to be huge. Just any small metal container, or you can make your own with piece of tin can, scissors and pliers