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External bed harness failed
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The WE I've been running at my desk just had the bed heater fail on it. I pulled the side panel and checked the wiring harness and everything looked good. The bed fuse seemed a bit warm, if that helps any.

Total print time on the machine was 17 days 12 hours 1 minute 4 seconds, with 70 prints on the machine.

Replacing the bed did not correct the problem. I will try tearing into the machine to see if I can find it.

Event Timeline

karrad added a subscriber: karrad.Aug 13 2019, 8:05 AM

@bigmansas If replacing the bed did not fix the issue, chances are a mosfet issue or wiring issue.

The external bed harness was the failure here. One line reads open loop once removed, on the machine it was giving us odd readings.

logan added a comment.Aug 13 2019, 8:29 AM

Here is a pic of the curve of it once removed

karrad renamed this task from Heating failed Bed to External bed harness failed.Aug 13 2019, 8:39 AM

Pulling back the braided loom, there is a prominent kink and/or bulge. I believe this location on the harness was right at the rear of the Y Cable Mount, due to the length of the braided loom on this harness.

adam added a subscriber: adam.Aug 13 2019, 10:37 AM

@logan what does that mean for the way we are building these cables? Are we going to see a lot of these fail in the field?

@adam it is possible that these could fail in the field. We've taken a video that shows how this cable may have been damaged. However the cable in the video is the bed harness not the bed power harness. The bed power harness in the video is the new replacement.

west added a comment.Aug 13 2019, 11:31 AM

If we did end up changing the printed part to help the cable we could remove a chunk for the cables to route around and move the face with the arrow back to make it more rigid right there

Would moving that face back make the bend at home even sharper? How will this prevent the cable from drooping into the frame as shown in the video?

west added a comment.Aug 13 2019, 12:36 PM

It looks like they start drooping right after the zip tie, by extending the face out further, we would make that section of cable a little more rigid

west added a comment.Aug 13 2019, 12:39 PM

Just spitballin

logan added a comment.Aug 13 2019, 1:08 PM

@bigmansas was wondering, what if we zip tied the 2 harnesses together maybe 2-3 inches behind the Y Cable Mount? On his unit anyway, only the one harness is drooping. Do you think that might help?

logan added a comment.Aug 13 2019, 2:06 PM

That catching on the bottom rear extrusion was reported in T7791 also

Here is an example of zip tying the wires together.

adam added a comment.Aug 14 2019, 10:47 AM

That doesn't look very good....

It looks better than the video I posted, and is the simplest potential solution.