TL;DR: If your bed heater fails check your board connector along with the wires for crispiness.
Resurrecting an older thread as it helped me out with troubleshooting what seems to be a problem with the Rambo boards on this and other printers.
I had my bed heater die on my Taz 6 towards the end of a print, with the firmware (Klipper) giving me a warning about the heater not responding. Traced all the wires checking for continuity, checked that the mosfet seemed to be functional, etc. Prior to pulling the whole board out I did a search on the forum and came across this thread. Pulled the bed connector off and found this:
Pulled the board out and found this:
One interesting note is that the fuse is fine. In reading up a little on these standard spade-style fuses, I learned that they don’t deal well with low-overload conditions (~110%-135% of rated current).Many will continue to conduct current @110% indefinitely, and can take hours to fail for greater currents. Looking into heated bed failures, I see a lot of burned pins and wiring harnesses, so the chosen fuse setup seems suboptimal relative to a significant cause of potential failure.
Also note that I found sputtering of material (likely solder) on the case directly behind this pin:
I’m not sure if this was because of vaporized solder condensing after sublimating, or if it represents high-current arcing to the grounded case. I did find it a little odd that a bare board with high-current pins is mounted over bare metal. I threw some kapton tape behind mine before reinstalling, just for my own peace of mind.
At first, I thought I would just replace the board. But I decided to just see if I could reuse safely as-is. I ran a 16awg jumper from the fuse holder, and spliced it into the 24V bed heater wire. Reassembled, and everything is working with no heating issues. I’ll keep an eye on things for now, but I couldn’t justify buying a new board at full price with the same design flaw.