Sharing this to help anyone else facing the same problem.
I tried to print something for the first time in ages. My SM2 A350 has printed less than 1.5kg of filament since new.
Everything seemed to be working OK to start with, the bed heated up for calibration, but when I went to start the job, the bed would not heat up and the job would therefore not start.
I had heard of an issue with cable wear on the heated bed, (Snapmaker 2 heated bed cable hazard - #33 by razgilbert) so I pulled mine apart to find the following:
If you look very closely there’s a tiny hole in the outer insulation with a single strand of wire poking through. I stripped back the insulation for a closer look:
The black wire (negative conductor for heater element) has snapped completely at the point where it joins the plastic clamp/cover on the heated bed.
The problem here is the lack of “strain relief” - i.e. something to limit the amount of flexing a the sharp join between the cable and the bed. Without this, the cable flexes repeatedly at this point which causes the copper to become brittle and snap.
To fix it, I cut all four wires in line with the break and re-soldered the original cable to the board, with some heat shrink tubing and self-amalgamating tape as makeshift strain relief. After re-assembling you can manually set the heat bed temperature via the controller and verify that it is working correctly.
It’s an easy fix, but you lose a couple of centimetres of cable each time. I’ve lodged a support request with the SM team to see if they’ve released a fix for this or to at least get them to supply a few spare cables so that I can continue to fix it in the future.
If you don’t want to disassemble the heat bed, but you do have a multi-meter handy, you can check the resistance across the pins of the heated bed cable following instructions here: https://support.snapmaker.com/hc/en-us/articles/360057401593-What-should-I-do-if-the-Heated-Bed-won-t-heat-up- Be warned though: the cable may be broken inside the outer insulation and only intermittently making contact, or making contact with just a single strand. If that happens, the multimeter may mislead you to believe the connection is OK.