desoldering pcb tips

[rmunson]

Hi folks - I'm preparing to do my first recap and I would appreciate any tips on desoldering the old caps from the pcb boards - I'll be working on an old magnavox solid state receiver.

questions:
When removing the caps, will I just heat each lead and wiggle it out of the pcb hole? Does it take very much heat to flow the solder and free the cap?

which tool will I want to use: solder wick or solder sucker - pen style vacuum pump?

How many seconds of heat on the pcb solder pad is safe?

any other issues I should be thinking about?

Thanks!
Reed

 

[Bob]

you need to decide for yourself what works best for you.

the last thing you want to do is to heat the joint then pull the caps. if you heat it too
much, then you might use pliers to pull. you could crush the cap (polystyrenes).
you will leave a glob blocking the replacement cap. third you will be using
very old (probably older than you) leftover used solder. and probably with NO
flux, damage the new replacement. then overheat the pcb and maybe lift those
traces that are tricky to fix.

the goal is to use enough heat for the SHORTEST POSSIBLE TIME, and
very quickly remove the solder. then the component drops off the board,
the through hole is clean, the board is NOT damaged. then replacing
the new component is a matter of mounting the cap, and using solder
(that has flux) to solder the component onto the board.

your tools and the device will dictate how effective it will be. cheap pencil
irons, static-free pencils, or temperature controlled - from bad to good.
solder suckers put lots of heat on the joint because the solder wick needs
to be heated up along with the joint. solder suckers require good hand-eye
corrdination, heat with iron with one hand, immediately switch to other hand with
sucker and release pump. or solder pump station

some notes, you may wish to clean up the board after pulling component.
do not attempt SMD boards as a beginning (there's a larger base of data
required for this OVER simple through-hole soldering).

UNDER NO CIRCUMSTANCES ARE YOU TO "FIX" CAP ORIENTATION
IF YOU SEE STENCILING ON THE BOARD THAT DOES NOT MATCH THE
COMPONENT AS IT WAS WIRED.

so to test and develop your skills. buy a working (or non working) unit.
remove caps and resistors and then solder them back in. find out
all the ways to do this and look for repeatability, reliability, speed
and correctness. reliability means that working unit continues to
operate after your work.

you'll also need a schematic, board layout, parts list and compare
this to the actual board - ALL four must agree in type, number,
value (and voltage if its a cap), etc. do not substitute unless
you have trusted information that you understand and can do.

good luck - post your summary and results with pictures if you wish
to return help to others that follow you. recorded mistakes OK to
help other learn.

 

[bigx5murf]

The problem is the leads are often bent in place before soldering. So when you try to wiggle it out just by flowing the solder, they catch, and can cause damage. I like to use a solder sucker, suck away the majority of the solder after flowing. Then more flux, heat it up again, and push the cap through more so I can take out the bend with pliers.

 

[rmunson]

The problem is the leads are often bent in place before soldering. So when you try to wiggle it out just by flowing the solder, they catch, and can cause damage. I like to use a solder sucker, suck away the majority of the solder after flowing. Then more flux, heat it up again, and push the cap through more so I can take out the bend with pliers.

ah - ok - I was thinking it was a one step process --
so heat the solder point, flow the solder, pop the solder sucker, straighten the lead/leg to help it go out straight --

What does adding more flux do in the process?

Thanks!
Reed

 

[slimecity]

If bent leads are inhibiting the process I like to heat the solder and pop the legs straight with a small screwdriver before pulling the cap.

What really works well for me is the solder wick - you can go thru quite a bit of it with large caps, but it works incredibly well. I still need to get onto using a solder sucker.

Additional flux helps for some processes like using the wick - the better wick has flux built-in, which helps the old solder stick to the wick.

Once you pick things up its quite straightforward.

 

[for_p1]

Hi folks - I'm preparing to do my first recap and I would appreciate any tips on desoldering the old caps from the pcb boards - I'll be working on an old magnavox solid state receiver.

questions:
When removing the caps, will I just heat each lead and wiggle it out of the pcb hole? Does it take very much heat to flow the solder and free the cap?

which tool will I want to use: solder wick or solder sucker - pen style vacuum pump?

How many seconds of heat on the pcb solder pad is safe?

any other issues I should be thinking about?

Thanks!
Reed

Get solder sucking device like make by Hakko. It is a must if you need to desolder more than a handul of components and do not want to deal with damages traces on PCB.

 

[bigx5murf]

ah - ok - I was thinking it was a one step process --
so heat the solder point, flow the solder, pop the solder sucker, straighten the lead/leg to help it go out straight --

What does adding more flux do in the process?

Thanks!
Reed

The reason bent pins can cause damaged traces is because even after sucking away most of the solder, the bent pin is still stuck to the traces with a small amount of solder. The flux is meant to try and heat that small amount so you don't lift a trace while trying to take the bend off the trace.

Also, yes a solder wick really helps in trying to remove those small traces of solder holding bent pins to traces.

 

[Steven Tate]

I made a video of the use of a Hakko FR-300 desoldering gun. It’s pricey at around $350. But if you plan on doing many of these, it’s worth it’s weight in gold. Component removal is quick and easy.
Steve

http://audiokarma.org/forums/index.php?threads/use-of-hakko-fr300-desoldering-gun-video.741463/

 

[Bob]

flux is like cooking in a frying pan without oil. the flux melts and transfers heat
to assist the solder/unsolder process.

it is always a good idea to add flux to a joint you wish to unsolder.

even the (de)soldering braids have flux.

 

[elnaldo]

For small caps I usually heat the soldering on one lead and pull to one side, then I heat the other lead and pull again from the capacitor bodie. What damages the traces is when you push the capacitor to the solder side. In small caps you can even heat the 2 leads at the same time.

I prefer to place the PCB in vertical position so you heat one side and pull from the components side.

In large caps I prefer to remove the old solder first.

To open the holes after removing one cap, I use a toothpick in the melt solder.

Do one cap at a time. Mark it with a marker before removing so you remember the original position. Don't trust your memory.

 

[Bob]

to add,

for caps, every one on the board, mark the negative side on the PCB,
even if you will use a non-polar/bi-polar in a polarized position
(the next guy may go anal and wish to revert to original),
and
ignore the stencil if it disagrees with the actual component.

and if you wish to totally avoid all possible explosions,
go bipolar unless you can't (in the power supply, for example).

document your changes in case you sell it.

 

[for_p1]

to add,

for caps, every one on the board, mark the negative side on the PCB,
even if you will use a non-polar/bi-polar in a polarized position
(the next guy may go anal and wish to revert to original),
and
ignore the stencil if it disagrees with the actual component.

and if you wish to totally avoid all possible explosions,
go bipolar unless you can't (in the power supply, for example).

document your changes in case you sell it.

I suggest to make high resolution (at least 13MP) pictures of board before any work. Shoot at different angles, so that you can see all sides and markings on components.

 

[petehall347]

one thing is if you ever feel the need to pull a component whilst solder is molten or not is never push towards the copper trace .always pull up off the board . with my solder sucker most things simply drop out after de-soldering last pin . always best to take good pics first . i sometimes mark all capacitors negative sides on the pcb for quick reference .

 

[elnaldo]

Leaving the Iron a bit more than you think helps to melt all the solder at both sides of the PCB. If not , you can damage double side PCBs when pulling the component.

I usually mark the capacitor body with a line pointing to the front of the unit, but marking the PCB is a good idea.

 

[Ray Gianelli]

The Hakko desoldering tool that's been mentioned is not cheap. But it's one of the few things that's worth every penny and then some.

If you're planning on doing this type of work then good tools are a must. And Hakko soldering and desoldering tools are excellent.

 

[for_p1]

Leaving the Iron a bit more than you think helps to melt all the solder at both sides of the PCB. If not , you can damage double side PCBs when pulling the component.

I usually mark the capacitor body with a line pointing to the front of the unit, but marking the PCB is a good idea.

That is why it is often easier to cut component first and then desolder pins one by one.

 

[elnaldo]

That is why it is often easier to cut component first and then desolder pins one by one.

yes, that's what I do when removing ICs with several pins, axial capacitors, or when I'm 100% sure the component won't be reused. But in medium sized capacitors you usually can't access to the leads under the capacitor body.

 

[rmunson]

Thanks a lot everyone - this has been really helpful!
I brought home a broken dvd/vcr player and did some practicing last night --

definitely did it wrong a few times -- glad I'm getting practice on a test piece --

feeling more confident to begin recapping my magnavox pcb boards....

desoldering off a newer pcb is technically going to require more heat than an old 70s board, correct? Since newer boards are going to be lead free and melt at a higher temp, right?

 

[gadget73]

Big +1 on the desoldering guns. I'm a big fan of my Hakko 808. It makes short work of this kind of thing, just heat and pull the trigger to get rid of the solder. In and out before any damage is done.

 

[Ray Gianelli]

Big +1 on the desoldering guns. I'm a big fan of my Hakko 808. It makes short work of this kind of thing, just heat and pull the trigger to get rid of the solder. In and out before any damage is done.

That's the one I have too. I can't say enough good things about it. Even though the newer model is more expensive, after my experience with the 808 I wouldn't hesitate to buy it should I need another desoldering gun.

Another factor is the importance of temperature controlled soldering/desoldering tools. Because IME not enough heat applied for too long is as destructive as too much heat.