Desoldering Bus Resistor [Sammich]

MIDIbox SID
1

FFS. This just had to happen: I put in one bus resistor with the wrong alignment. Position RN1. I am trying to desolder it since over 2 hours but I have no chance.

I have a soldering sucker and desoldering braid and I did remove some solder. However, the resistor is still mounted to the pcb rock solid. I tried to lever it out but I did not use brute force because I can damage the pcb contacts I think. I know the net is full of desoldering tips but I feel helpless at the moment. Any idea, maybe a RN1-specific one?

:cry:

2

ok , nevermind, there was actually already a question like that and it looks like i have to cut this thing out and order a new one. God damn.

3

depending of your soldering skill and iron quality, you can use desoldering wick. Results not garanteed

the easiest is to sacrify your SIL Resistor and get a new one

4

desoldering is the real art, isn’t it? At work I have a powered desoldering iron. At home I recommend either using a sold-a-pullt with your regular iron, or else a desoldering iron with a rubber vacuum bulb.

http://www.elexp.com/sdr_0822.htm

http://www.elexp.com/sdr_0849.htm

both are pretty cheap. I find braid only good for smt or non-plated holes.

Usually at home I use the bulb iron. Start with a fully soldered joint. If you have previous unsuccessful attempts to desolder, fully fill the holes with solder again.

Before applying the iron to the board, squeeze the bulb fully. Then put the iron on the solder joint. In a second or two the solder will melt.

Do not press down hard against the board or else you might lift the pad. Move the iron back and forth or in a circular motion as you quickly release the bulb. Do not stop moving the iron! You want the lead to be moving while you suck the solder out and immediately remove the iron. If there is still a little solder left in the hole, the lead movement will help prevent the solder from bonding to the component lead.

Now put your finger on the component (in your case the resistor network) and wiggle it a little while you look at the lead on the other side of the board. Does the lead wiggle? If so, good job! If not, wait for the hole to cool and lightly prod the lead with your fingeernail or blunt instrument. Hopefully the lead will work free easily. Do not apply force or you can damage the board.

Maybe you can’t work the pin free. Don’t worry. Move on to the next pin, and try again, starting from a fully soldered joint.

Keep doing this until you’ve finished every pin. Ideally the component will just fall out, but maybe you have 1 or two pins that are still sticking. You can try to apply heat to one hole while gently wiggling the component. Keep wiggling it even after you’ve removed the heat. When the trace amounts of solder in the hole harden back up, they will most likely not bond to the pin.

I’m pretty experienced with this, so I’m confident to do it without damaging a board. In the past I’ve ruined my share, so if you’re unsure, you’re better off cutting the component off and replacing it.

You want to avoid wiggling or moving the solder joint when it’s hot but the heat has not transferred to the solder. In that case the only thing that will have any flex will be the adhesive that bonds the copper to the board, and that’s how you lift pads and traces.

Good luck.

5

If your aim is not to salvage a part (i.e. it’s easily replaceable), then I advise sacrificing the part, chopping it into single pins which are then easy to desolder. You save a lot of time and it is less risk damaging the pads.

After you get the part out, removing solder from small pads is tedious and annoying. I often use a vice to hold the board vertical, edge towards me, so I can heat the pad with a soldering iron from one side while sucking solder from the other. Sometimes adding more solder to the pad can help, so there’s more of a blob to be sucked out, i.e. if it’s only a tiny bit inside the hole, this can be hard to get into an easily suckable state.

I have plenty spare resistor networks so just email me and I’ll post you a new one.

6

Heat up all the joints at once with a mini blow torch and whack it on the desk.

7

Thanks guys for your support. I ordered a new resistor, they are really cheap. To a noob like me it was quite surprising HOW cheap most standard electronic pieces are.

The most striking tip that you guys gave me, is that, if you want to desolder something, it might be a good idea, to add even more solder first. I will remember that.

8

add more solder permits to keep high temperature (like a big ice against a tiny one in Springs)

i’d advise the same, and "clean " with soldering wick after

9

Thanks guys for your support. I ordered a new resistor, they are really cheap. To a noob like me it was quite surprising HOW cheap most standard electronic pieces are.

Be sure to check it is a “common pin” type resistor network… i.e. 5 resistors… and not the other kind with 3 separate, unconnected resistors.

10

Here’s another tip. There is this stuff called Chip Quik. It is like solder-however, the melting point is much lower. So you “solder” this stuff onto your joints. Then heat up all joints simultaneously by lying your iron somewhat sideways. Because the Chip Quik stays molten longer, you have more time to melt all the joints. Highly recommended for difficult desoldering jobs. I have the pumps and the braids, and the Chip Quik is way better for tough jobs.

11

Wow, that quick chip stuff seems to be very good. In this video, they guy smoothly heats up 4 sides of a chip, 1 after 1 and then simply takes the chip away. So the solder seems to be very hot and liquid for a long time. Thanks for the hint.

As for my problem, I finally removed the resistor after cutting it into pieces and then removing it pin by pin. Afterwards I placed the PCB so I could heat the joints from one side and remove the solder with a solder-sucker from the other side. Like Wilbe described. So far, the Sammich seems to work well but I gotta check it’s behaviour more in detail over the weekend. I actually found a problem, but it seems to be java-editor based.

12

Do I flag this thread as **FIXED** ? :wink:

13

Yes you can unless we wan’t to turn this thread into a general desoldering thread :slight_smile: