Desoldering silver solder - Page 1
Forum section: electronics / beginners

author: msknight
author_rank: Regular Contributor
timestamp: July 19, 2021, 01:37:32 pm
content: I'm trying to re-work a board on a piece of audio kit which looks to have been done with silver solder. At the moment, I've been working it by melting in 60/40 and then using solder wick, but I'm concerned that I'm not getting at the solder which is inside the holes and the damage I could do with all this heat.Short of cutting the legs off the pot and potentially not being able to find another (I'm not sure if it's easily replaceable) I'm a bit stuck and I thought I'd ask for some advice, before I irreparably damage something.EDIT - I'm happy to cut the legs off if I can identify it and get a replacement, as I think it's faulty (and either needs a good clean out, or replacement) ... it's just that I'm not sure I can yet, and I don't have a service manual.

author: TimFox
author_rank: Super Contributor
timestamp: July 19, 2021, 01:44:13 pm
content: Assuming you mean SN62 Ag2 Pb36 ternary-eutectic soft solder, it should behave very similarly to the familiar SN63 PB37 binary eutectic. Sn60 Pb40 has a slightly higher temperature, but is not eutectic. To clear a hole, I find a simple round toothpick works well after removing the bulk of the solder. Unfortunately, cutting the legs off a pot or DIP IC is often the simplest way to remove stuff from a TH board, so long as you do not need to salvage the part.

author: Andy Watson
author_rank: Super Contributor
timestamp: July 19, 2021, 02:30:20 pm
content: Another vote for chopping the leads off - if you are sure that it's faulty, you've got nothing to lose. Working the board, trying to remove the awkward solder is (in my opinion) going to result in more damage.The pots look like Alps, or clones of. For example:https://www.ebay.co.uk/itm/164669240987Useful search terms are Alps, snap-in, log-taper, plus whatever resistance value the pot is.

author: msknight
author_rank: Regular Contributor
timestamp: July 19, 2021, 03:12:43 pm
content: OK - I've chopped the legs. No markings on the back. The side has 53325b but I can't find anything of that kind of part number. So... next job is to find out how I work out what value/part this is. Any hints please before I get buried in datasheets?

author: msknight
author_rank: Regular Contributor
timestamp: July 19, 2021, 03:30:56 pm
content: Found a datasheet. The pin outs don't seem to match, but the pins are small, so as I've wrecked it anyway, I'm going to solder small bits of wire to each one so they are easier to put a meter on and diagnose.

author: msknight
author_rank: Regular Contributor
timestamp: July 19, 2021, 04:41:21 pm
content: OK - It seems to be 10K but the pinouts don't match the datasheets I've found. Pins 3 and 4 are wipes, but connect to pins 2 and 5, and 1 and 6 respectively.So how do I find the replacement for this please? Just go through loads of datasheets to try and find one, or is there someone I can contact?

author: Andy Watson
author_rank: Super Contributor
timestamp: July 19, 2021, 05:24:43 pm
content: I'm looking at an Alps datasheet, and the pin-out,not the numbers, corresponds to their "15C" variety in their RK14K range. Do the measurements match?Also note, the numbering on the back of the PCB indicates that the pins are not numered in the obvious linear manner that you would expect!

author: jpanhalt
author_rank: Super Contributor
timestamp: July 19, 2021, 05:25:29 pm
content: I agree about cutting the pins off and have done that often. There are two other options I have used:1) Hot air will allow simultaneous heating of all or most of the solder joints around leads to be melted, and gentle rocking while heating will free the part; or2) Add a very low temp solder (e.g, ChipQuik) to make an much lower melting alloy, then do #1 or use a regular soldering iron.The caveat is to never pull hard, particularly while hot, as that risks pulling the plated hole out along with the pin. You then have a much more difficult repair and tracks attached to the hole are also damaged.As for clearing holes after desoldering, I use a fine braid of solder wick. The tip of the iron pushes enough of the braid into the hole to clear the solder.

author: msknight
author_rank: Regular Contributor
timestamp: July 20, 2021, 06:57:41 am
content: Progress report... not much.The pot was cut off and measured, but I can't find anything in Alps 14K range that matches the shaft, bush and resistance values... so I e-mailed Alps.This is looking to be a part that was made specifically for Teac. As such, even getting a replacement would likely be the same, "batch," and if the pots are the fault(as there are a number of people on the internet reporting the same volume issue with the AI-101DA)then the chances are that the replacement would probably have the same issue.I'll update if I make any progress, but I have written this up on my personal blog -http://msknight.com/technilife/?p=1245- so if you're interested then maybe look in on it in a months time to see if there's an update.Many thanks for all the help. Every encounter is another chance to learn...

author: wraper
author_rank: Unknown
timestamp: July 20, 2021, 07:13:54 am
content: I'm 99.9% sure it's a completely usual lead-free solder which is used everywhere these days.

author: jpanhalt
author_rank: Super Contributor
timestamp: July 20, 2021, 09:41:59 am
content: @msknightI looked at your blog. If you can find a pot that matches electronically (i.e., same pinout and resistance), and if it sorta fits, adjusting for a different shaft size is easy. One can even compensate for bushings that are different.

author: msknight
author_rank: Regular Contributor
timestamp: July 20, 2021, 01:24:31 pm
content: Quote from: jpanhalt on July 20, 2021, 09:41:59 amI hope my blog didn't bore you too much! - I've found this -https://tech.alpsalpine.com/prod/e/html/potentiometer/rotarypotentiometers/rk14k12/rk14k1240036.html- and ordered some of those from LCSC, as it was either them, Japan or USA. Oh well, it will be, what it will be. What's the worst that can happen? Magic smoke?

author: msknight
author_rank: Regular Contributor
timestamp: August 12, 2021, 07:03:13 am
content: Just thought I'd say thank you, and deliver some closure on this.Alps didn't respond to the e-mail request for help. However, their part RK14K1240036 was almost identical, except for a slightly smaller shaft(I thought it would be 5mm longer)and it has a, "bump," in the middle of the wipe.Other than that, it went into the Teac and it didn't blow up under initial testing.(although the volume knob currently falls off)Now I have to apply speakers and do a soak test to see if the pot was actually the issue... although there's a good chance that the heat is causing another component to change tolerance/values somewhere else in the chain... but I'm at least one step forward.Thanks for all the help. I've made worthwhile progress and haven't required the assistance of the fire department

author: Andy Watson
author_rank: Super Contributor
timestamp: August 30, 2021, 04:31:07 pm
content: Quote from: msknight on August 12, 2021, 07:03:13 amMiserable sodsQuoteDOH!Something has been bugging me about the "bump" in the middle. Having just read your latest blog I now realise what that bug was. A centre detent suggests that the pot is intended for a tone control, or possibly a pan control, i.e. its taper is not logarithmic. I think the part that you want will have what Alps call a 15A resistance taper - part number RK14K12D0A1XPerhaps too late for you, but next time have a look at RS stock number 154-8182

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 03, 2021, 07:23:17 am
content: Thats just rohs solder, specially early alloys were a pain to rework.You can find low-temperature melting alloys, bismuth and/or indium based, which will make the proccess much easier.Also, pre-heating the board will help a lot in repair like these.

author: coppercone2
author_rank: Super Contributor
timestamp: September 03, 2021, 07:38:35 pm
content: if you chop the legs chop them directly at the part with flush cutters, I have destroyed a part thinking I can pop the cut leg out of the hole but then it ends up being too short and you can break the lamination playing peakabooyou can bore out parts slightly if there is a slight misfit using copper/brass laps (speed lap) with diamond paste in a drill to very slowly enlarge the hole size if you make a franken potentiometer.http://www.acrolaps.com/to make a knob sit tight on a too small shaft, the easy way would be to buy copper shim and wrap it around the shaft after you cut it nicely and stick the knob on top of that so it fills the difference.I recommend a desoldering gun, I don't think I read a single forum post that actually thought that not having a desoldering gun at the beginning of the hobby was a good idea.. usually when you finally use one you go 'oh shit, what the hell have I been doing'. I wish I bit that bullet in the beginning. Crappy desoldering technology cost me tons of problems actually...

author: tooki
author_rank: Super Contributor
timestamp: September 06, 2021, 11:51:46 am
content: I concur that a continuous-vacuum desoldering system is absolutely worth it. Solder suckers and wick were perfectly adequate for single-layer boards, but plated through-holes are very hard to reliably desolder with them.