On an earlier post, I mentioned I was working on a new preamp kit. (See here) On that post, I temporarily used a vintage St. Ives Input Transformer for my prototype since I ran out of my Carnhill Input transformers.
Now, I’m going to replace that St. Ives Input Transformer and use the actual Carnhill Input Transformer model that the NK-72DI Mic Preamp Kit will be using.
TIP: DESOLDERING MULTI-PIN PARTS
I used to dread desoldering multi-pin parts (like IC chips, sockets, DPDT switches, connectors, headers, etc.). I used to own and use those plastic desolder pump thingy… Which is crap. I end up just ruining and lifting the pads because my soldering iron stayed on that one spot too long, trying to suck up the solder. Not good. I’d eventually ruin a good board, and had throw it away (along with the components) and rebuild a new board again.
There has to be a better way to desolder… so I researched a bit, and got a Hakko 808 desoldering gun several years ago. Oh my goodness! This is so easy… it’s like soldering in reverse! Why didn’t I bought this at the start. I’m really very happy with the Hakko 808 and I can now unsolder and remove multi-pin parts without damage to the PCB, or to the part. Yes, it’s not a problem even on double-sided, plated through holes. (I think someone buying a soldering iron should also buy a desoldering tool at the same time! There should be some unwritten rule about this.)
So that’s the first tip… get a proper desoldering tool! Also, when desoldering parts, it helps if you add fresh solder to the joints or pads, and/or add liquid flux. This makes the old solder easier to suck out and the wet flux also spreads the heat to a bigger area. This makes the desoldering process faster, and therefore less chance of damaging the pads or component you’re trying to remove.
Sometimes, when you’re trying to desolder a part that’s soldered to a big, thick ground plane, the heat from the desoldering gun’s tip isn’t enough… the ground plane just sucks the heat away from the pads. And then you end up heating the joint too long and therefore risk damaging the pads. In these cases, I sometimes preheat the board using either a hot air bath, or a hot-air reflow gun. When the surrounding area is hot, then I use the desoldering gun to finally suck out that solder. Easy peasy! And the part easily falls off the board. Done!
So this is the part we need to desolder. Its the St. Ives Input transformer, bottom view.
It’s soldered to a double-sided board with plated through holes, so we need to be able to suck up the solder on the other side of the board too. Otherwise, our part will still be stucked to the board.
Using the Hakko 808 desoldering gun, we did the job cleanly without damaging any pads. Took maybe just over a minute to do all these pads. The trick is to heat the component pins for maybe 2-3 seconds, then push the desoldering tool flush with the pad so the solder melts and get soft, then pull the trigger and let the desolder pump do it’s work of sucking up the solder.
And now we have the new transformer part soldered in place, board cleaned with 99.9% IPA and pat-dried to a shiny finish.
