How to test board thermistor reading

gorf26

I have my bed thermistor hooked to the duet thermistor 1 input , and i am getting a -90 reading
I tried 2 different thermistor's and i am fairly sure both are good..

I connected a multi meter to the pin on the board and with power off i was reading around 6.5 K ohm
power on it was 28 K ohm.. on thermistor 1 pins..

I connected to thermistor 2 input and was getting 76k ohm power off and 253k ohm power on.

So there is a big difference between the two doe's it sound like input 1 is bad ? or do i need to test in a different way? and is it a easy repair if needed..

Thanks gary

alankilian

@gorf26

What board do you have?
Please post your config.g so we can see your thermistor configuration.
You can't test for resistance with the power on.

But you still have differences between therminstor inputs 0 and 1with the power off, so that's interesting.

Did you have the thermistor disconnected when you were taking this measurement?
Where did you have the other end of the Ohm meter connected?

gorf26

I will have to get the config file later but i have not changed anything in the config and it was working fine last time i used this printer..

it's a maestro board

i did have the thermistor disconnected when taking the readings.
I placed a 2 pin connector on the thermistor pin's with wires inserted and tested across the 2 wires .

I also tested the two thermistor's while disconnected across the 2 wire's, I forget at the moment what the reading was but they were the same for both thermistor's.

Thanks gary

dc42

@gorf26 I give a thermistor input a quick test by connecting a 100K 1% resistor across it and configuring it as a thermistor input without specifying parameters in M308 other than the sensor number, type, and port. That should give a reading close to 25C.

gorf26

@dc42

Thanks What i ended up just trying was changing from the thermistor 2 port to the thermistor 3 port and setting the new pin number in the config no other changes to the config.

and it's working correct temp now, so looks like the input on 2 for the thermistor is bad.

it there a easy way to fix it, or just forget it and go with what i have running now, I don't picture ever needing a 3rd thermistor...

Gary