For the past month, my Makerbot Cupcape extruder had progressively more trouble extruding. After some research, I found others had this problem too. It seems to be due to an undersized "H-bridge" chip driving more than it should.
A few weeks ago, I decided I should have another complete set of Gen3 electronics on hand just in case I had a failure such as this. That way, I could swap boards if one went bad and not be "down" while I repaired the other board. However, the Gen3 board set has been consistently out of stock at Makerbot for a couple months. In the mean time, I'm not completely out of options. It turns out that there are two extruder motor driver circuits! In Skienforge, going into the extruder board settings, you can change from the primary extruder driver (using 1A, 1B) to the secondary driver (using 2a, 2b). Still, that just solves the symptom, not the problem. The real cause of this might just be my motor is drawing too much. For now, I've hooked up the extruder motor to the secondary extruder driver circuit. But I'm thinking that this failure is likely to happen again. So, what are my longer term options?Option 1) Install the Makerbot Stepstruder upgrade kit. Even though this upgrade is listed as "Experimental" I have a reasonable expectation that this would work. My order is in, but it will be a while before this solution arrives.
Option 2) Replace this chip with another of the same kind. I probably could rush order the chip from Digikey and try my hand at soldering it in. However, even if I did accomplish this tricky surface mount soldering operation, it's likely the new chip might just blow out again!
Option3) Replace the wimpy chip with something a little heavier. Fortunately, someone else decided this was a good idea too. So, they documented the fix!
http://wiki.makerbot.com/gen3-hbridge-fix. Makerbot even lists the kit on their site!
The problem with option3 is that Makerbot is now out of those parts too! Fortunately, they still had the bare board available. So, between what I have in stock in my workshop, a rush order from Digikey and a trip down to Radio Shack, I now have the parts needed to make that repair. Since my secondary circuit still works, I'll be printing out a bracket so I can mount this secondary board directly above the extruder board. Hopefully, my secondary extruder circuit will last long enough to do that print!
I am disappointed in the supply problems Makerbot seems to have. As you may have guessed, buying components from several places then paying retail prices per-component, has boosted the cost of this fix by quite a bit.At times like this, I'm reminded of the Monty Python Cheese Shop.
http://www.youtube.com/watch?v=B3KBuQHHKx0
However, in spite of these problems, Makerbot still has one really good thing going for it. It's the fact that the device is an open design. That means I have a fighting chance of fixing this myself. If this product was proprietary with no schematics and secret firmware, and the company went out of business, I would be totally out of luck. Even though the Gen3 electronics apparently aren't very robust, they are at least an open design with a vibrant user community. That means this repair is annoying rather than impossible.
