What's new
By:

Blast City PSU Recap - Can't remove old solder on caps

GhaleonUnlimited

GhaleonUnlimited

Enthusiast
Joined
Dec 20, 2021
Messages
217
Reaction score
119
Location
Cleveland, Ohio
So I'm recapping my Blast PSU and the solder is like ridiculously thick and stubborn. I have a nice Hakko solder/desolder+air compressor station, that's temperature selectable, and my desolder gun is barely making it melt. I tried adding solder, then desoldering again, but this really doesn't help much. The new solder can't seem to really gel with the old so it can all be sucked up.

I'm worried about damaging anything if I crank the desolder gun temp way up or apply pressure to the caps, and I'm bad at trying to put in new caps with solder in the through-holes still.

What are common solutions in this situation?
 
What temp are you using? Make sure to add some good flux as well. Sometimes when I run into this issue I run hot air on the joint on solder side to get it molten then quickly suck it up with the desoldering gun on parts side (you have to clip off or pull the component out first) to protect the pad.
 
Flow new solder and flux over the joints (they are old and crusty on these psu's 9 times out of ten)

Increase heat

if you have a heat gun you can preheat the copper planes some before attempting removal.

Other options, walking the caps out then wicking the solder off
Using a soldering iron and your desolder gun together
 
One more vote for more heat!

higher temperature and higher heat are slightly different things... What we're fighting here is thermal mass.

pumping higher temperature directly into the joint doesn't work exactly as expected for the reasons others have mentioned above - big ground planes (like the ones that PSU caps re often soldered to) have a lot of thermal mass, and they can wick the heat away just as fast as the tip of a desoldering tool can transfer it in.
Cranking up the temp can burn the local area and start to delaminate the board while leaving the solder relatively unmelted.

Getting more heat into the joint might require a different approach
If the board is tightly packed with heat-sensitive components sometimes I use a normal soldering Iron AND the desoldering tool on the joint at the same time to pump lots of heat energy directly into the joint
Or if thats not possible - gently preheating the entire area with hot-air means the tip of the desoldering tool has a much easier time.

And the reverse is also true, when soldering the new caps on it's easy to create a cold joint, lots of flux and lots of dwell time for good joints on big connections
 
You must log in or register to reply here.
Back
Top