‘Torque Limit Errors’ have both the 1650 and 2000 offline, and as the 2000 has a few other things :::: the 1650 seems the place to start.
The heads that I have for my machines are:
FDM2000 — Soluble Support (stripped model tip thread), ABS (Torque Limit Errors), & ICW
FDM1650 — ABS (Torque Limit Errors)
With all this stuff you would think there would be a combination that would work.
Although the heads look the same, they are not. The electrical connectors are different 1650/2000. The dowel pin spacing/pattern is different between the 1650/2000 feed blocks:

FDM2000 Left — FDM1650 Right
In addition the number/material (and probably size) of the feed rolls is different (one pair/two pair), motor size/gearing, the notch in the base plate for the protruding gear different too… arguhhh…
The FDM1650 ABS head model side seems almost siezed compared to the support side, and that seems to be the cause of the Torque Limit Errors. The motor seemed also ‘stiffer‘ that the support side motor.

Model side feed block and motor
When I removed the blocks, the model side had a coating of black grease, like lithium grease, but the support side had a white grease, like Krytox. Perhaps the last person to redo the model feed block didn’t want to spend the big bucks on the good high temperature grease?
Also, the feed rollers on the model side appear to be in direct contact with the block, where on the model side there seems to be some clearance (where did I put the feeler gages?).
Everything seems to be pressed fitted together, except for the pin holding the motor gear and the three screws attaching the motor to the block.
So, over the next couple of weeks I hope to be figuring this out (after I find the small bench press) and I’ll try to take pictures and get into the blog ….
Anyone who’s done this before, I love some comment pointers from you.
—-John