Bed Preheat Error - Wiring Problem
Recently I started receiving Bed Preheat Errors. Following the troubleshooting steps on help.prusa3d I noticed that the printed bracket for the where the wiring attaches to the bed was warping. I removed that and found what you see in the photo, the wiring is stripped and exposed on red, and the bed harness had even melted around it. This is a four year old printer, I accept that this may be a simple case of "wear and tear" but I'd like to have some confidence before making that decision.
Please let me know if I have a deeper problem I should be looking for, or any additional safety precautions I can/should take in the future.
I'm comfortable with wiring/electronics/soldering, etc. Is there a place I can find out the gauge of these wires to create a new pair?
More than anything I want to avoid a safety problem -
Thanks for reviewing!
RE:
The discoloured crimp terminal on the red cable would suggest localised heating of the terminal. Heat has been conducted back up the wire which has melted the sheathing and exposed the copper.
Two possibilities in my mind: 1) The screw connection to the PCB was not tight enough resulting in a higher than normal resistance and consequent localised heating. 2) The crimping operation for the terminal was done poorly with the same result.
From the picture, there seems to be a washer stuck to the crimp terminal. Was the washer fitted on the top side of the crimp terminal or sandwiched between the terminal and the PCB?
To check the integrity of the crimp, see what happens if you try to pull the crimp terminal off of the red wire. Compare that to doing the same thing to the black wire.
Prusa support should be able to give you the wire specification for replacement.
Cheers,
Tim
RE: Bed Preheat Error - Wiring Problem
Thank you for your prompt reply - apologies for the delay in responding. The black you see in the photo is from the melted bed heater cable mount. I replaced the assembly with new wiring and so far I believe that has resolved my issue.
RE: Bed Preheat Error - Wiring Problem
I might be mistaken but it looks as if the washer was installed between the ring terminal and the copper trace on the heatbed. It should be installed on top of the ring terminal with the ring terminal in direct contact with the copper trace.
See the install step 3 here:
https://help.prusa3d.com/guide/7-heatbed-psu-assembly_172872
For safety sake, please insure you’ve reassembled this per the assembly guide.
Cheers