How to fix your burned extruder board

Burned extruder board (check out the chip on the right)

Burned extruder board (check out the chip on the right)

Once I was sure my extruder board was burned out, I placed an order for a new extruder board and a new fiddly bit.  For those of you with similarly burned boards, it is part “A3949SLBT.”  I honestly have no idea what it actually does or how it works – just that it controls the power going to the extruder motor on my 3D printer.

Thanks to the many people who read this blog, there were a lot of suggestions on how to fix this problem.  I ended up using a method that was a hybrid of several suggestions.  This was mostly due to me not having a lot of specialized tools or products handy.

Here’s what I did:

  1. I read a web page about how to desolder a joint.  It seemed pretty straight forward.
  2. I dusted off my soldering iron and SMT Soldering Kit.  From the kit I pulled out the solder paste, tweezers, and soldering wick.
  3. I pulled out about an inch of the soldering wick and bent it at the end.  I then pushed the tip of my hot soldering into the bent piece of soldering wick and the soldering wick into the joints holding the chip in place.  I chose to start on the side of the chip that was nearest the edge of the board.
  4. I pulled up as much solder as I could by pressing the wick into the solder joint, clipping the pieces of used wick, and repeating.
  5. I then tried to pull that side of the chip up – but that didn’t work.  There was still some solder holding it down.
  6. I then used a pair of wire cutters to clip all of the leads on the side nearest the edge of the board.  Using a small precision flathead screwdriver I pried up the leads on the chip.
  7. Half-desoldered and half-cut fiddly bit

    Half-desoldered and half-cut fiddly bit

    Using a pair of needlenose pliers, I bent the chip upwards so that I could get underneath it.  It was now attached only by the leads closest to the inside of the board.

  8. This left me with a chip suspended in the middle of the board and little bits of leads still stuck to the pads on one side.
  9. Again, I used the soldering iron to hold the wick against the remains of the leads.  I used a little back and forth brushing motion, parallel to the pads, which seemed to work well to basically either solder the lead bit to the wick or brush it right off the board.  Once I was done, the pads were relatively clean and smooth.
  10. I then used the soldering iron to press the wick against the underside of the chip where it was soldered to the board – picking up as much solder as I could.
  11. I then bent the chip back down and pulled up as much solder from the top of the leads too.
  12. Chip removed

    Chip removed

    At this point the chip easily popped off – but I could just as well clipped the leads and soldering iron-wick-brushing motioned them off too.

  13. Here I was left with the soldering pad relatively clean, but a little worse for the wear.
  14. I then took the new chip and applied soldering paste to its leads – a long line across all of the leads on each side.  I then used a toothpick to pull apart the solder holding any two leads together.
  15. I used the small fine tweezers from my SMT Soldering Kit to place the chip in the proper orientation.  (Pro tip: Zach was kind enough to design the board so that the semi-circle on the chip should match up with a semi-circle drawn on the board itself).
  16. I used the toothpick again to clean out any solder between any two leads.
  17. Resoldered new fiddly bit

    Resoldered new fiddly bit

    I then briefly touched the soldering iron to each lead, which very quickly turned molten silver and flowed around the lead and onto the pad.  This went quite quickly.

  18. I hooked the extruder board up to my Cupcake, but it didn’t work fully.  I could register temperature and heat the extruder, but I couldn’t move the motor at all – which was the first symptom I had anyhow.
  19. I disconnected the extruder board and used my multi-tester to test for continuity between each lead and solder pad on the chip.  While I was at it, I decided to test to see if any two neighboring leads had continuity.  A few did.  At first I was worried then I tried to test the second fiddly bit chip – which had continuity in the same sets of adjacent leads.  Next time I have to do something similar, I will definitely test the joints before testing the board.
  20. I found two leads that were not adequately soldered to their pads, added a little more soldering paste, and touched the joints again with my soldering iron.
  21. This time testing was all good!

Thank you to everyone who posted suggestions and volunteered to help me!

Just in case you’ve burned out the same part, MakerBot has listed part number “A3949SLBT.” 1

  1. But, if you e-mail them and tell them MakerBlock told you to ask for the “fiddly bit” they might know what you’re talking about. []