Heated bed kit debug help

[pmeyer 0]

 

Just added a heated bed kit to a UM1. Unfortunately, I get no heat.

Everything else works (x/y/z, extrusion, nozzle heat and temp sensor). With bed temp set to zero, I get fine prints (on blue tape).

With bed temp set to 70, set point shows as 70, but measured temp stays 0. Bed stays cool.

The fact that bed reads 0, not ambient of ~20, makes me think more than one thing is wrong. If it was just the heater driver, I'd at least see ambient. If it was just a bad or disconnected temp sensor, the heater would go on (but possibly overheat).

Thermistor resistance is about 109 ohms at ambient. Heater resistance is about 3.7 ohms.

Help?

Paul

[gr5 2,237]

Thermistor resistance is about 109 ohms at ambient.

 

Perfect. But where did you measure the resistance? Try measuring underneath the printer. Often you get an open where you screw down the wires on the bed or in the solder joints where the terminal block solders to the heated bed.

Have you ever inserted a 4.7K resistor in the circuit board? If so you need to remove it. This detail is not mentioned I believe in the instructions.

 

[pmeyer 0]

Perfect. But where did you measure the resistance? Try measuring underneath the printer. Often you get an open where you screw down the wires on the bed or in the solder joints where the terminal block solders to the heated bed.

Have you ever inserted a 4.7K resistor in the circuit board? If so you need to remove it. This detail is not mentioned I believe in the instructions.

 

Thanks for the help. I never modified the main board. Could the resistor have come with the printer?

I'm measuring on the exposed 90 pins that go to the thermistor connector on the PCB (see below). I'm getting 108.9 now.

By the way, how do you disconnect the power supply from the heated-bed PCB? Once I connected it I can't seem to get it off. I see there is a slider on the end, but pushing it or pulling it still doesn't seem to release the connector. No big deal for now, but eventually it would be nice to be able to remove it.

I get 108.9 right now.

 

[pmeyer 0]

Perfect. But where did you measure the resistance? Try measuring underneath the printer. Often you get an open where you screw down the wires on the bed or in the solder joints where the terminal block solders to the heated bed.

Have you ever inserted a 4.7K resistor in the circuit board? If so you need to remove it. This detail is not mentioned I believe in the instructions.

 

Solved!

The three wire jumper from the heated-bed kit PCB to the main board (temp3) is defective. 5v and Signal both have a good connection, but the middle (ground) is open (infinite resistance measured from the exposed pcb pin to the mainboard pin).

Replaced that cable with three loose jumpers and I read 19C on the bed, and it heats up!

I'll start a test print while I see if I can repair the jumper.

Paul