Mini 1: RAMBo fan not spinning without assistance, leading to probable overheat condition

Edit:

The bulging problem disclosed here looks very similar to what I am experiencing.

Post:

I have a Mini 1 purchased in 2018 and used semi-regularly since, not sure of the manufacture date. The printer communicates with Cura LE over USB. No screen, no MicroSD. The printer is fairly well maintained, clean, dialled in, lubricated.

The case fan for cooling the RAMBo board (I believe v1.3) no longer spins without assistance, in the form of poking a (non-conductive) spudger through the case to set the fan spinning. When the system is idle and the fan isn’t running I can hear a faint intermittent but frequent electronic buzzing/squeaking noise which might correspond to a PWM signal.

I’ve performed a fairly solid diagnosis that correlates either:

  • Overheating of the RAMBo board;
  • The fan not spinning,
  • or both.

Particularly, I have ruled out the host computer and USB cable.

With transient loss of print fidelity, typically manifesting as what I suppose is either:

  • Overextrusion.
  • Dropped commands or failed hot end moves.

I strongly suspect the latter. This loss of fidelity is in the form of layers which are wider than expected, which produces a print which is ribbed in the x,y plane with unacceptable dimensions. I attribute this to a missed z-step. In such prints the hot-end retraction at the end of the print is anomalous, pausing for a fraction of a second at about 1 second intervals. Unfortunately I don’t presently have any examples to take a photo of.

If I set the fan running manually by pushing it with the spudger, I get basically ideal prints.

I have popped the case and run the fan up to 24 V DC and it seems okay. I think the minimum voltage for spinning up unassisted was about 5 V.

I request assistance and advice in diagnosing what is going on here. I have read other threads and discussions on Lulzbot specifically and RAMBo more generally, and suspect 5 diagnoses/courses of action:

  1. Fan is dying, replace fan (need to know precise model).
  2. Fan is dying, increase PWM duty cycle in firmware or G-code (how?).
  3. Fan power MOSFET is damaged (replace MOSFET).
  4. Fan power MOSFET is damaged (replace RAMBo).
  5. Fan power MOSFET is damaged (patch fan directly into PSU and purchase hearing protection).

Assume I have:

  • Amateur to intermediate electronics skills.
  • Amateur to intermediate microcontroller programming proficiency.
  • Strong Linux proficiency and a Linux box.
  • An oscilloscope, multimeter, bench PSU, soldering iron.
  • Very limited SMD desoldering and reflow capabilities (specifically a Miniware MHP30 hotplate).

Thank you in advance to anyone who takes the time to lend their expertise.

I run 6 Mini-1s. Familiar with Mini Rambo cooling issue.
Your fan gave your 6 years of service. You did well.
All fans fail. they have moving parts. Most commonly The bearings. Sleeve Bearings sooner than Ball Bearings.

Replace the fan. Make sure you get a fan with Ball Bearings. Additionally review the rated life of the fan. Go for the longer service life. The CFM rating of the fan is also important. Look for higher values. Again, Most important is Ball Bearings.

Yes. The Rambo in the Mini runs hot. When hot the stepper drivers will “flake out” and miss steps.

While you have the cover off, install heat sink(s) on the driver chips. Either 4 individual heat sinks or a strip that covers all the drivers. They are about 3/8 inch square. Get ones with the adhesive already on.
Best of luck, Mitch

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It sounds like you’re plenty capable of throwing it on another PWM source on the board and seeing if the fan operates normally to rule it out as a point of failure, but for reference, the exact fan is found in the bill of materials as “Pelonis FAN 80x80x15 High flow”, part #C8015H24BPLP1b-7.

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@mburko @Wrathernaut Thank you very much for your advice. I have replaced the fan with a Sirocco YX2452 and capped the stepper drivers with copper PGA heatsinks intended for a Raspberry Pi. Faint squeaking/buzzing still present but maybe this is just choke whine. The fan spins up without assistance and print quality is ideal. n.b. that this filament is a bit wet and my Z-offset is quite high because I like it that way.

Additional notes for anyone who runs into this problem:

  • The YX2452 is a 25 mm tall fan. This means that the existing screws are too short, however 32 mm M3 screws are a good fit with the existing washers and backplate.
  • Because the fan is taller, there is less clearance for the wiring to the board, but everything squishes down acceptably.
  • You can just cut the adapter off the Pelonis fan and solder it to the Sirocco leads (with heatshrink or some other insulation).

Hopefully I can get a few more years out of this beast.

Kind regards and thanks again.