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Error: Temperature reading fault on heater 0: sensor open circuit

Posted by Sardi 
Error: Temperature reading fault on heater 0: sensor open circuit
December 20, 2017 08:56AM
I recently re-did the wiring on my Ormerod 1 bed thermistor and since then Im getting the Error: Temperature reading fault on heater 0: sensor open circuit msg.

I cant see where the circuit might be open, Ive checked and rechecked over and over again and cant see what Im doing wrong.
Checked the board for burns, its clean, no burns that I can see. (This is my second board, Ive burnt the L7 on the first one so I would know grinning smiley )

The crimps on the thermistor are original crimped by RepRap.

EDIT: tried rewiring, double checking the connections, squeezing the wires, restarting every time etc.. nothing I do seems to change the situation..

EDIT: I have it working, but now it reads +361C

EDIT: out of nowhere back to the same open circuit msg

Edited 6 time(s). Last edit at 12/21/2017 11:31AM by Sardi.
Re: Error: Temperature reading fault on heater 0: sensor open circuit
December 25, 2017 04:09PM
Could be a failing input, wire, connector, or thermistor.

First thing I'd try is swapping the thermistors for the heated bed and hot end around to see if the other inputs read the same. If the thermistors for the heated bed and hot end are not exactly the same you may need to fiddle the config file to get this to work properly. Don't run the heaters when you do this it's just to see if the hot end thermistor input can read a value properly and the high temp reading moves to the heated bed.

If the fault moves as expected above I'd disconnect the thermistor from the board and check the following with a multimeter:

Check reading as close to the thermistor as possible. You'd need to find a table of expected values for room temperatures to compare it to or wait for someone else to chime in here with a target value.

If the above works then I'd connect the plug that connects to the board to a multimeter in a hands free manner such as croc clips of the back of flying leads shoved in the plug. Remove all the tie wraps that are connecting the section of the loom to the machine and gently flex the wire along it's length to see if you get a big increase in resistance at any point. Pay particular attention to the sockets or any solder joints. If you see this then you need to run some new wire for the thermistor.
Re: Error: Temperature reading fault on heater 0: sensor open circuit
December 27, 2017 08:45AM
I got a hold of a multimeter today.

The readings are 4K on the board, 10K on the thermistor.

Ohm1 Ohm2
I have also disconnected the thermistor from the ribbon and the value for therimstor alone was 10K.

I think its safe to say that the thermistor is gone, but the ribbon and the board are ok.
Re: Error: Temperature reading fault on heater 0: sensor open circuit
December 27, 2017 12:15PM
Sorry when I said check at the noard end I meant the lead to the thermistor on the plug that connects to the board.

Judging by this thread 10k is a valid reading:

[forums.reprap.org]
Re: Error: Temperature reading fault on heater 0: sensor open circuit
December 27, 2017 01:07PM
I read that topic, and the guy has Ormerod2 and problem with hot end so its a different thermistor in question.

I am in contact with Adrian from RepRap and he told me the following

But there is one crucial test you can easily do - with everything powered off measure the resistance
across the two pins top left which are the alternative place to plug the thermistor in.  The
thermistor wires in the ribbon cable are in parallel with these, and so that will measure the
resistance of the thermistor through the wires.  If all is well you should get a reading of about
6K.  This will drop slightly if you put your finger on the thermistor to warm it.

If you get a reading of about 10K then the thermistor circuit has a break somewhere.

Now, to be fair, I do have 4K on the board, and 10K on the thermistor.
Im certainly not smart about this.
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