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[mmaness]

Wow! I desoldered the two 20 pin chips (U4/U5) in less than 20 minutes!

They're already installed in the correct direction (I'm so stupid!) and the board is tested - and works!!

Here's what I did:

At lunch today, I went to Radio Shack and bought a desoldering iron and a tin of paste flux. The desoldering iron is a 45 watt iron that has, instead of a soldering tip, a hollow tip that's attached to a rubber bulb. The deal is that you squeeze the air out of the builb, hold the iron on the soldered connection, heat it up for a few moments, then quickly let go of the bulb. Because the iron is in contact with the connection when the vacuum occurs, it's still in liquid form. And if you'll put the iron's hollow tip flush with the circuit board, most of the air drawn into the bulb will be thru the board, bringing solder from all inside the connection.

While the iron was in contact with the connection (5 sec or so), I would move the wire around a bit, trying to squeeze every bit of solder that I could out of the joint. And after I used the bulb, I'd put the iron over a sheet of aluminum foil to get the solder out of the iron's tip. Works much better (IMO) than the traditional solder s u c k e r.

The idea of the flux is that flux not only pre-cleans a connection immediately prior to soldering, but it also helps tremendously in getting solder to flow. The solder we use is rosin core solder - rosin is the flux inside the solder 'wire'. The rosin has pretty well burned off after a connection has been soldered (that's the brown and black that's on the iron after you use it for a while). So by putting a little rosin paste flux on the connection, it helps the solder to flow from the connection to the desoldering tip.

Now - there's no real way that 100% of the solder has come out. Inside the hole that we put the leads thru in the circuit board is a little metal tube that runs the width of the circuit board. There will be just the tiniest bit of solder left.

So after you get all the solder out that you possibly can, carefully (and I mean CAREFULLY!) take a small screwdriver, place it under one end of the chip, and slowly lift. You might even rock it back and forth a bit to get it to break loose. But it'll come out, 'cause there isn't a whole lot of solder left in there. I also have a curved needle nose pliers that I use to help lift it out.

After it's out, I used desolder braid to remove more solder from the joint, straighten the IC chips pins, place it back in the board (the correct way this time, dummy!), and resolder it.

That's all there is to it, folks .. easy peasy, lemon squeezy. No big deal. It took about the same time it's taken for me to write this as it did to desolder one 20 pin chip.

Dan did suggest that I could also use a can of compressed air, but I prefer the desoldering iron/bulb combo from Radio Shack. It's about $15-$16 or so, and it money well spent.

Dan did kindly offer to fix it for me if I'd send it back, but like Tim, I really didn't want to have Dan have to bear the costs and trouble of my stupidity. So instead of paying shipping charges and waiting a couple of weeks, I spent $20 (desoldering iron and paste flux) and fixed it myself.

So for anyone else that solders their chip in backwards, there is hope. And while most web sites on the internet suggest cutting off the leads and replacing the chip with a new one, I'm here to tell you that it's easy to remove. Just be patient, be gentle, and have the correct tools - and you CAN successfully remove a direct solder IC chip.

Mike Maness

[Tim Fischer]

Congrats!

I have that exact same desoldering iron -- bought it when I was probably 13 or 14 for model railroad use. Mine's a bit worse for the wear, though, and wasn't working that well for me. I think it might be clogged up inside... I should probably just invest in a new one someday.

Definitely works well wen it's working like it should, though... With the "solder suckers", the solder always seems to firm up the instant you remove the iron, and it always takes me a few seconds to position the vacuum tip properly and by then it's too late to get all the solder...

As I noted above, I did purchase desoldering braid, but I was impatient and did my desoldering before it arrived. But now I have it in my bag of tricks to try for my next screwup

-Tim