desoldering oxidized contacts

Zinfer

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Was running a cap kit on a Operation Wolf sound board and main board. I got through about 9 of the electrolytic caps on the main board and it took like half the day to do it.
The pins would not heat up to be removed without bumping up the heat and actually pulling the part on one side, while the iron was on the other. I usually like to use a low temp solder extractor, but it just wouldn't work.
I ended up having to put heat on component side as well to pull the old electrolytics off.
Job is about done, but wow. Is there anything that could make this job a bit easier?
Obviously it's a 1987 board, so not near as old as an early 80's board. Never had so much trouble getting old parts off. And the solder points on the solder side were just a very small amount, where my extractor would go completely over the point without touching any solder.
 
Add fresh solder before attempting to desolder. Another option is to add flux if you have a flux pin or bottle.

If the original solder is oxidized, before I add any new solder, I brush the oxidized solder pads with a soft brass brush that looks like a tooth brush to remove as much of the oxidation as possible:

brass brush.jpg

These come in handy for cleaning the legs of ICs as well.

Bill
 
I second Bill on this one. I use it alot.

Well, the sad part is, the white oxidation was actually under the caps on component side. It would not heat up correctly at all to loosen it. Took me about half the day to get them all off.
 
Uh.....you don't mean they were glued right ?

I never saw "white" oxidation under a cap and the components side...I mean where does that sit, on the wires or on the PCB ? They weren't leaking caps ?

Adding a little new solder to get old solderings running is the most overlooked/ignored tip about soldering it seems......without doing that you are pumping loads of heat into the part/soldering before it starts running, that is IF it ever starts running. Using some flux works the same if you have it around.
The flux in the new solder makes the old solder running again.
 
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Curious: What made you replace the caps on the main board? Just age or was something not working?

I too brush the pads and add new solder. Seems to work.
 
Curious: What made you replace the caps on the main board? Just age or was something not working?

I too brush the pads and add new solder. Seems to work.

The audio board, which sits on top of the main board of an Operation Wolf was not giving the sound it should. Very weak, crackly. I've got the audio pots on the board and on the cabinet pumped all the way up and I'm just getting muffled sound. First thing I thought when I saw that entire line of caps, was that they probably should be replaced. While I had the boardset out I also felt it a good time to swap the caps on the main board with new while I was there.
I didn't know they were going to be that difficult to actually get out. The solder from circuit side would not flow completely to the component side. In some cases I had to clip the legs of the caps to get to the underside of the component to apply heat directly there. I tried adding fresh solder, I also tried braid. Neither solution worked.
I have never tried flux to remove components, but if that would work in the future I'll have to pick up some. These things were stuck solid.
Also, the Taito boards of 1987 seem to use alot less solder, like half the diameter. So when you put your desoldering iron down on the circuit side, it actually creates a circle on the pcb as the tip's diameter seems too large. Typically you can just offset the tip so that it makes contact with a portion of the solder and that usually does it. Not in this case. In this case the Pace desoldering iron wouldn't suck any of the old solder out.
 
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Brass or steel brush to clean. You can also stand the board vertically heat the offending pin/solder from the "bottom" side and add fresh solder to the top of the pin (not top of the board) and allow it to flow down - the new solder will carry away the old solder - then you simple remove the new solder. This method works great, but wastes solder.

Soldering circuit boards vertically is also a good way to solder them as well since you can never add to much solder as the excess will move away with the iron, plus it is a quick way of soldering in an IC as you just move down the row of pins with the iron and a 'flow' of solder - learned this way back from my days in tv repair in the 80's.
 
So what do you use to hold the board in place? I often use this method when trying to remove a component. But it's hard since you really need that 3rd hand.
 
The audio board, which sits on top of the main board of an Operation Wolf was not giving the sound it should.

Yeah, it makes sense to change those caps. Bypass caps in audio circuits dry out and cause sounds issues all the time. I wouldn't have bothered with the caps on the main +5 line though.
 
Yeah, it makes sense to change those caps. Bypass caps in audio circuits dry out and cause sounds issues all the time. I wouldn't have bothered with the caps on the main +5 line though.
Imagine my surprise when this didn't work...I was so confident it was the caps.
 
That sucks, but more reason to get an ESR meter...
Now there's an idea. But don't you have to remove the caps anyways to test them? Any of those ESR meters out there that you could affordably recommend?
 
Now there's an idea. But don't you have to remove the caps anyways to test them? Any of those ESR meters out there that you could affordably recommend?

Depends on what you mean by affordable. I've got a Fluke 87III and its got a cap test mode. Works great as far as I can tell. I do think you have to pull the caps from the board but next time I'm checking caps I will try to remember to test them off and on the board.
 
So what do you use to hold the board in place? I often use this method when trying to remove a component. But it's hard since you really need that 3rd hand.

I bought one of these and mounted it to a board attached perpendicularly to a piece of particle board (the base). Works great.

holder.jpg
 
I bought one of these and mounted it to a board attached perpendicularly to a piece of particle board (the base). Works great.

holder.jpg

That is a great idea - but to answer the question, I just usually lean it up against something that I have handy at the time so it varies. It is something I have done since the 80's and have gotten use to it, but the above idea would be perfect for those that could use the extra hand.
 
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