Does mini Rambo v1.1b need a Z-stepper driver heatsink?

Hello all!

Working on a Mini v1.02 that I got second hand, and have fixed nearly everything wrong with it (replaced a few printed/purchased parts, fixed threaded inserts that had popped out, etc.). While working through the behaviors and issues, I noticed that the Z-stepper driver on my Mini Rambo v1.1b had the thermal adhesive residue, but the heatsink was long gone, not even in the case anymore

Should I replace this now-missing Z-driver heatsink? Was it removed in a later revision or service bulletin? I can imagine the Z-stepper has a more difficult life due to the two-motor-load, so I am hesitant to leave it as-is since it was clearly there to begin with.

I’ve cleaned off the adhesive residue in the meantime, and visually inspected everything for damage and heat-discoloration, and found nothing frightening, but I want to ensure long-term reliability. I welcome everyone’s thoughts on the matter.

Thanks in advance!
M Yurkoski

Leave the heat sink off. They had been known to fall off and possibly short out board components.

They stopped installing them when they did a little testing and found that “there is little to no difference in chip temperatures with and without the heat sink. The slight difference is within experimental error.”

I had problems with the Z driver overheating and skipping steps - causing some disastrous print failures - after the heat sink installed by Lulzbot fell off.

I recommend reinstalling it, but not with the adhesive pad as used by Lukabot. That adhesive pad just isn’t sufficient given the orientation of the board/chip.

I reinstalled mine using some 2-part Arctic silver thermal epoxy. No more skipped steps, and the thermal epoxy won’t fail like the adhesive pad originally used.

These chips have built in thermal protection and really do not require the use of the heat sink.

If you experience skipped steps, you may have improper case cooling and at that point you could look into installing it.

The possibility of the heat sink falling and shorting the board outweigh the added benefits unless absolutely necessary.

ScottW, if you have any photos of what the failures look like, this could be very instrumental in diagnosing my issue. I don’t have outright catastrophic failures, just crappy print quality with a ton of banding that seems to increase as I add things like z-hop. I’ll post another thread on this issue, with photos.

McLeach, I appreciate all the feedback here. I did see that service bulletin, but it is for the Taz 6, which is much newer than my far older mini v1.02 (euphorbia), so I have no idea if the driver IC is the same between the boards (i have no Taz 6 to test against). Additionally the copper pours and PCB-sourced thermal evacuation is almost certainly not the same, so it may be incorrect to assume that the Taz6 bulletin should apply to the 1.1b Rambo board. Its tough to know without an in-depth thermal analysis or the creator’s input.

I do agree that there is risk to it falling off, and I’ve seen some of the horror stories when it lets go. I’d definitely use a thermal epoxy like ScottW suggested if I added it back. I’d have to buy another one since I don’t have the heatsink anymore

I will create another thread with photographs that demonstrates why I have zoomed into this missing heatsink. I’m not sure they are related, so I don’t want to muddle the intent of this thread. It sounds like the original creators of this board are not easily accessed anymore, so it is unlikely we will get a definitive answer.

I may attempt some thermal images of the chip package to help determine a Tjunct temperature, and post the calculated results to this thread.

Long time ago, I posted photos to the “old” Lulzbot forum but not sure what happened to all that. Can’t find them now.

But basically what happens is the next layer is laid down at the same Z (or almost the same Z, as sometimes not a full layer height is skipped) as the previous layer. Eventually the print head can impact the model hard enough to break the print, or pull it loose from the bed. If you aren’t nearby to cancel the print, it can create one heck of a mess – as the printer just keeps going, keeps extruding, pulling the print around the surface and adding spaghetti to it.