PCB repairs

[jim]

Here is a broken PCB mounted pot from a modern production amp with 7 solder connections holding it to the board. I have flush cut the leads and sucked and wicked.
It won't move and I do not want to pull up a trace.  I am thinking of sectioning the housing with a thin disc in my Dremel to remove one leg at a time. Is this the way to do it safely?  Jim 

[EL34]

It's hard to get all 7 solder points to release even though you sucked the solder


I would dremel the side supports if you can't get it free the way it is

[jim]

Thanks!

[DummyLoad]

like doug says cut the frame away. the frame is sucking too much heat so solder won't reflo.
if you pull a frame trace no biggie, slip a lead wire through or solder both sides of the board.
reflo the holes that won't come free with some new solder, then suck the solder out again. many cases the solder crystallizes and that's you're only recourse is add fresh solder.   


don't flush cut next time. a lot of times, i cut the part out leaving the pins, i'll heat on the solder side, suck the solder and pin through on the component side, if the pin won't come out, then i'll reflo, heat the lead and plate-thru and pull the pin out from the component side - here you have to be fast or you'll pull a pad/trace and/or a plate-thru
. try not to roll the iron on the traces, that rolls them up into a nice little ball. not good. if the component pins had an inference fit in the hole before the manufacturer reflo, then pulling the plate-thru and/or pad(s) is sometimes unavoidable. pins that are bent over to lock the component before initial reflo can be a bugger too.


modern CE PCBs are not really meant to be serviced. they are built as throwaway.


--pete

[HotBluePlates]

3 of the solder tabs are for the pot, the other 4 are for the bracket which hold it. I don't know if all 7 need to come undone in order to replace the pot.

The "right way" to do it, which PCB manufacturers use, is to attach a special bit to the soldering workstation which is square- or rectangle-shaped. The bit will contact all solder joints simultaneously so that all release at the same time and the part can be removed.

Unless you do a LOT of these repairs, the special bit isn't worth the expense (and it won't fit just any soldering iron). Doug told you right about trying to cut it free as much as possible.

[EL34]

Yeah, maybe the supports are separate from the pot?


I was assuming the frame was part of the pot

[jim]

I will cut the housing away and will see if it falls away from the pot.  There is a ferrule of some sort holding it there.  The replacement is solidly connected. Jim

[jim]

Here is the new pot ready to solder.  Loosening those tabs on the face of the broken shaft pot only made the back of the pot fall away--the brass ferrule held it tight to the frame.  I dremeled the frame between the feet close to the board and then snipped the remaining bit with fine wire cutters to avoid damaging the board. Thanks for your help.  Jim

[jim]

Sorry, here is the pic of the finish.

[Willabe]

Looks real good, nice job!


              Brad     

[G._Hoffman]

I've always been able to cut the frame bits with just a side cutters, since the material has to be of a solderable nature.  Then you can unsolder the various pins one at a time, which is a heck of a lot easier!


Gabriel