How To: Bed Thermistor Replacement

After a while, the bed temperature on my Robo3D was reading zero in Repetier-Host and would not heat up. This is how it was fixed:

1. Determine if the thermistor is bad: Switch the hot end thermistor connector with the bed thermistor connector on the PCB. After being switched, if the hot end now shows zero temperature in Repetier-Host, you know that the board is fine and the thermistor is bad. That was my case. T1 is the bed thermistor and T0 the hot end thermistor.



2. Turn off the printer, and unplug the USB cable. Remove the power supply cable from the back of the printer and unplug the power supply cable from the wall. Do know work on anything, including the Robo3D printer, while it is plugged in or could be accidentally supplied with power.

3. As I began to take the heated bed off the printer, the problem became evident. The thermistor wire had broken.



4. Disconnect the bed heater and bed thermistor from the board;

5. Remove the heated bed, by undoing the four bolts. You'll have to remove the plastic piece that holds the end of the Y belt. Make note of how the belt feeds around the pulleys and cog.

6. The broken thermistor wire is more evident after the bed is removed and turned over.



7. Remove the tape holding the thermistor, cut the thermistor wire, and remove the thermistor. Here is the new thermistor and tape as supplied by Robo3D.


8. Strip the wires and join (solder) the new thermistor. I held the wires together with a @PCBGRIP clamp as I soldered. Notice the heat sink tubing.


9. I slipped some more heat shrink tubing (yellow tubing in the pic) and taped the new thermistor to the bed. Hopefully the additional heat shrink will prevent the wire from snapping.


10. Reinstall bed, wire up the heater cables to the board and plug in the thermistor. Set the Z height.

 

Thanks for writing this up! I broke my thermistor a long time ago and I've been stalling on doing the repair. I'm thinking about fitting removable plugs on the thermistor and heatbed wires to avoid problems if I ever need to move something out of the way.

 

Had a broken wire on my heat bed also. Tear down, re solder broken wire, heat shrink the new connection, Kapton tape it to the bed, and zipped tied the thermistor wires to the Heat Bed wires which are a little beefier.
I like your pics "Jag" they turned out very good.