CTC Heated Build Platform Thermistor Fix

thingiverse

Many, many owners find that the Heated Build Platform on their CTC Dual Printer (which is a clone of the Flashforge Creator, which is in itself a clone of the Makerbot Replicator Dual), is woefully badly calibrated. The HBP is based on the original Replicator HBP ( http://www.thingiverse.com/thing:16061 ), but the PCB layout is tweaked to make space for a largish (~7mm) thermistor, or a 1206 SMD part (only 1 should be fitted though). In many ways, it doesn't really matter if the displayed (set) temperature doesn't match the real HBP temperature, so long as it's consistent. However, on my CTC, it was out such that a set temperature of 90C resulted in a platform temperature of about 60 degrees, and the maximum allowed set temperature of 130 degrees resulted in an actual platform temperature of 90 C. That's not good enough - the inaccuracy means the HBP isn't really hot enough for reliable ABS prints. The reason for the discrepancy is that CTC chose the wrong part for the thermistor. I'm not sure what the part is they used, but it's beta is way out of the required beta. I'm running Sailfish 7.7, and according to the source code, the firmware is designed to work with a 100k thermistor with beta 4066K with R2 at 4.7K. So, replacing the thermistor with a better part will fix the problem. I chose to use an EPCOS B57540G0104J thermistor. Which is absolutely tiny, but works very well. You should be able to find one on RS, Digikey, Farnell, the usual suspects. Replacing the thermistor Step 1 Remove the HBP by fully removing the 4 bed levelling wing nuts, and disconnecting the power connector Step 2 See the original thermistor in the centre of the board. Use your soldering iron and a solder sucker and/or solder wick to remove it. Worth keeping as a spare. Step 3 The two unused pads next to the thermistor are where we'll solder the new one. The new thermistor is tiny. Make sure the legs are not twisted and shorting out before you install it. Step 4 Solder the new thermistor about an inch away, onto the SMD pads. Apply a small piece of kapton tape to keep the bead of the thermistor in contact with the board. Finished, with a piece of kapton tape to hold the thermister against the board Step 5 Reassemble the printer. Make sure to tighten the levelling nuts a lot so the platform is definitely low enough to start your bed levelling procedure. You don't want to ram your extruder into the side of it. Finished! Use the monitor tool in ReplicatorG to set a test temperature for the HBP Now the temperatures measured on the underside of the HBP are within about 2% of the set temp, and the surface temperature is a little lower than that. When I set 130 degrees, the underside of mine is at 127 and the top surface gets to 118. Perfect! Happy Printing.