During heat up, build bed temperature falls then jumps to 1024C

Summary:

During heat up, build bed temperature reading falls to near zero and then jumps to 1024 on ToM with Stepstruder MK7

During heat up, build bed temperature falls then jumps to 1024C

conceivecreate 06 Jul 2012 21:06

Till last week my machine was working good – then I decided to peel off the painter tape from the build platform, clean the platform with acetone and tighten the X and Y belts. Now that everything is back and reassembled, the heated build platform reads about 75C (give or take a few degrees) while the extruder temp reads 30C (as I would expect on a hot summer day). Via the Control Panel, if the command is set to platform temp of say 100C, the bed temperatures rises (as I can put my palm and feel it getting hot) but the platform temp reading falls! It continues to fall to near zero and then becomes 1024C and remains there. Of course, I switched off the unit to ensure that I do not burn up the bed. The extruder and corresponding temp sensor seems to be functioning normal as I have taken it to 220C and extruded ABS plastic. I have checked the wiring from the build platform to the Controller – there does not seem to be an issue there. Other functions like “calibration” are working perfectly.

Following Jetguys’ response to query by fezza68, titled “False Heated Build Platform Reading between 107-114 on or off, on the PCB of the build platform, I measured for resistances across ground (pin 1 or black wire), and the signal wires (pin 3 white wire) (=should be 100K resistance) and between the ground (pin 1 black wire) and power (pin 2 green wire) (= should be 120 ohms)

It appears that have Open Circuit across both these combinations (though my wires are good)

Has my build bed gone bad? Any suggestions?
Other than replacing the Heater Board, is there something else that can be done?

Background information
I do not remember, but I may have removed the 6 wire wiring harness from the build platform while the unit was connected to the 120V main.
I have tried to shut down the unit and the computer multiple times and restart and reboot
I have RESET on the Motherboard Shield by PRESSing the RESET button (may have read that this will clear our readings)
I have RESET on the Controller by PRESSing the corresponding RESET button (not sure why I did this?? was it a BAD IDEA??)
Build bed was originally the ABP but I have disconnected the motor and removed the belt so now it functions like HBP. These motor leads on the heated build platform are disconnected
I am using Generation 4 Electronics on my ToM with Stepstruder MK7.
MakerBot® MotherBoard v2.4, Arduino Mega 2560 Core, Extruder Controller v3.6, Stepper Drivers v3.3, Mechanical Endstop v1.2, replicatorG 0034 and Skeinforge 35

Re: During heat up, build bed temperature falls then jumps to 1024C

Jetguy 07 Jul 2012 11:37

The extruder controller has a safety routine in the firmware that if it detects the thermocouple of the extruder head or the thermistor of the heated bed open circuit or short, it displays 1024 as the temp for the offending head/bed until either the reset button on the extruder controller or the power is cycled on/off. This is safety since it is a feedback circuit and loss of the temp probe would cause the heater to be stuck on.

Fix your wiring-that's where the problem is. Most likely a loose connection.

Re: During heat up, build bed temperature falls then jumps to 1024C

conceivecreate 07 Jul 2012 13:58

Jetguy - thanks for your response. It appears that you are leaning towards a loose connection in spite of my reading of Open circuit resistances across ground (pin 1) and power (pin 2). I measured this directly at the pins (of the heated circuit board) and not at the wires. This should normally be 120 ohms. Correct?

Re: During heat up, build bed temperature falls then jumps to 1024C

Jetguy 08 Jul 2012 02:04

Exactly and likely, because the connector isn't strain proof, you have damaged the PCB through handling while doing your maintenance. That's why people kept going through these and I've had one fail on me too. After that, they all got epoxy over the connector to the PCB and cable strain protection.

Re: During heat up, build bed temperature falls then jumps to 1024C

conceivecreate 12 Jul 2012 03:37

Just to finish and report on the outcome … replaced the 6 pin wire harness while keeping the old heated build plate -> Same problem
Replaced the heated build plate with brand new one and replaced the 6 pin wire harness => problem solved.

So while doing the regular maintenance and / or accidentally removing the 6 wire harness with the machine ON, I destroyed both the 6 wire harness and the heated build plate. (Any one tried repairing the HBP? How?)

Indecently, I have opted to add the Aluminum plate on the Heated build plate. I intend to use painter's masking tape and when made avaiable, I will use the Kapton tape.

Hopefully, happy building now…