For the heck of it, I decided to find out why the motor failed. There was a remote possibility the motor gears might just be jammed. Maybe a bit of oil is all it needs! So, I took it off the extruder assembly. The gear box in front of the motor seemed OK.I then separated the gearbox from the motor. I then powered up the motor with a 9V transistor battery. It seemed to run but it was a bit rough. However, since I have no idea how the motor normally operates, I decided to put it all back together and give it another go. Just for good measure, I also decided to put a lighter grade of oil in the gearbox. A 9V battery was still able to turn the motor once the gearbox was reassembled.
I then re-installed the motor. Using the control panel, the motor-gearbox seemed to have no trouble extruding a steady stream of plastic. It also started and stopped OK many times under the control panel. However, when doing a print job, it would still fail unpredictably when doing a raft. Sometimes it would make it as far as the 2nd or 3rd layer. However, I could not get a reliable extrusion past that point no matter the thumbwheel setting was. Taking some measurements showed that the DC driver circuit seemed to be doing it's job and the status lights on the extruder board are also helpful in showing that the circuit section is either working or not. Taking apart the motor showed that the gearbox seems OK. However, I've still declared the motor officially broken.
By broken, the motor rotates without it's gearbox, but it runs rough. I suspect when the motor is at a rough part, this causes the extruder board to sense something strange is going on. So, the extruder board then shuts the channel down. This is easily observed when lights on the extruder channel stop working. I eventually learned that shutdown can be prevented by going into Skienforge to put a smaller maximum extrusion value. If the motor is stalled, voltage levels are still maintained so it seems that the board is doing it's job. However, all that doesn't matter since the motor doesn't rotate! What is interesting is that the same behavior was seen even with the add-on driver board. So, maybe channel shutdown is caused by a noise issue? Maybe the motor momentarily shorts (or opens)? Hard to say without having another known good motor to compare this behavior to.
Of course, Makerbot is out of these replacement motors. The community has mentioned that the geared motors don't hold up well and even Makerbot admitted that they now know they had a bad batch of motors go out the door. Makerbot does not offer these motors anymore. So, I ordered a batch direct from Kysane. Since they have a large minimum order, I'll be selling what I don't use via Ebay. Note, this order was en-route PRE-Earthquake so these motors are NOT radioactive Yay!!
