Replacing Melzi stepper drivers?

Hello, I blew out the stepper driver for my extruder on a Melzi v1 and I don't have the cash to get a new board. Has anyone ever successfully desoldered and soldered on a new a4988 IC on a Melzi? I have a friend who has a Melzi that he doesn't need. My soldering skills are mediocre at best and I don't have a hot air soldering station.

EDIT: Also note that my friend has an entire Pololu driver for a ramps that he is not using.

Thanks,
jakobnator

Edited 2 time(s). Last edit at 07/02/2014 03:12PM by jakobnator.

You can do it, but you have to improve your soldering skills a bit, be patient and very attentive
You need a low power soldering iron (e.g. 20-30W) or better a soldering station, with a relatively fine tip.

Desoldering the good A4988 - I assume the Melzi of your friend has at least one A4988 in good condition, but is not good as a replacement board as a whole
The procedure will try to desolder the pins on one side, while slightly rotating the IC body along the long axis ((the complicated part), then free it up by desoldering the pins on the other side (much simpler)
- firmly fix the board on the working table, for example using power tape on the short edges; this is because you will need both hands and also a non-moving board
- place the tip of a cutter or similar under one of the short edges of the A4988 to be desoldered; it will not initially get under, but eventually will
- move the tip of the soldering iron along one pinned edges of the IC, starting from the side you also have the "extraction tool" (the cutter); repeat the move fast, trying to warm up all soldered pins on the side; try not to come too close to the IC body, to limit the heat it receives
- simultaneously, push constantly the tip of the cutter under the IC; do not press very, very hard, and try to seize the moment when the body starts to "take off" the PCB; be patient with this; once you succeed the problem is more than half solved
- continue to warm the pins, and to push and rotate the tip of the cutter as a lever, trying to rotate the IC body around the other long edge of the IC
- do not overheat too much the pins or you may destroy the chip by overheating it; it's hard to say how much is too much; you should better take a break, blow over the circuit to cool it down, understand what you achieve, and what not and why and... persevere
- do not force the "lever", or it might be the copper pads and tracks will detach from the PCB which will most probably be hard or even impossible to repair (you might not be interested in this case, since it is about a "donor" PCB, but might be useful in other circumstances)
As you can observe it's a very delicate operation, and you may end up with a burned IC, and there is no way to know this before you solder it on the new board and discover it doesn't work.
Therefore I strongly advise you to buy a new IC.

Desoldering the bad A4988 - This will assume you have a Dremel or Proxxon or similar with a fine cutting disk. If not, you can proceed as above, but be more attentive at the risk of braking the tracks or pads.
- gently cut all pins just near the plastic body of the defective IC; keep the tool firmly and take care not to let it go crazy in any other direction then the intended one and not to touch the PCB, just cut the pins pushing the tool easily down enough only to do cut the pins and no more
- once you get rid of the plastic body, use the soldering iron tip to remove the remaining part of the pins (they will normally try to stick to the tip of the soldering iron; clean the tip as soon as you "catch" one)
- do not overheat the pads, they are very small and easily unstick from the board
- clean the pads and the PCB in the IC area; some isopropyl alcohol will work for this ; it should look as nothing was ever soldered there

Soldering a good A4988 - Well, there are good tutorials on YouTube for that

Here are some more recommendations:
- find a more experienced friend to do the job
- buy a new A4988
- use a soldering station and adjust it to the minimum temperature that still melts the solder fast (perhaps around 280C)
- work fast, but pause as frequently as you feel at risk of doing something bad (let your technical common sense "seize" the danger)

And yes, you can also hook a stepstick, but that's another story, I would say a bit more complicated in a sense

Good luck!

Thanks for the tip I will try your method, I never thought of cutting the chip out with a dremel. Thanks!