Hotend temperature and heating issue
January 02, 2019 03:28PM
Hi all,

back online after a long time, my Ormerod v1 was operating perfectly till a few weeks ago. It's a standard machine with dc42's IR differential sensor. Now the reported temperature for the hotend is always false :
- 32°C when "cold". The room temperature is actually between 10°C and 16°C (it's a veranda without heaters).
- when heating the hotend, for example requesting 100°C, the reported temperature raises very fast until ~100°C, within a few seconds. But the hotend doesn't actually heats, which looks normal to me as the sensor reports the required temperature and thus the firmware stops heating.
- if the thermistor is disconnected, the reported temperature is between 9 and 10°C, the fan starts and the hotend heats up to ~50°C

What did I try to fix it :
- totally decommissioned and recommissioned the IR differential board, the hotend and the sensor
- checked all the connectors and the connectivities, both visually and with a multimeter.
- replaced the thermistor with a 100k resistor : the loom is ok, but the reading using both Pronterface or the HTTP GUI reports a temperature ~39°C
- changed the thermistor with a new one, exact same model.

I'm now totally stuck, the only part I couldn't check further is the Duet board. Now I'm afraid that some port of the Atmel has been damaged, thus the bad temperature reporting.

Does anybody has any idea to investigate more, or, even better, to fix it ?

Thanks
Patrice
Re: Hotend temperature and heating issue
January 02, 2019 04:48PM
Have you updated the firmware, or changed config.g recently?

To me the symptoms sound like you've got a 4.7k board , but M305 isn't set to reflect this.

Quote
linked webpage
If you have a 4.7K board, and don’t make this change, your temperatures will report very high at room temperature on both the hot end and heated bed, and will over-read at the target temperature
Re: Hotend temperature and heating issue
January 02, 2019 05:40PM
Thanks for your answer.
Nothing changed in config.g for months, not to say years. My Duet is a 1k version, I've done the checks from your link and both resistors are marked 01b. The bed temperature is reported as expected, no issue with it. Anyhow I'll check it again tomorrow night.
Re: Hotend temperature and heating issue
January 03, 2019 11:55AM
Very odd.

Thoughts:
  • If M305 isn't set, perhaps try setting it to force it to the correct value?
  • Whilst this Duet wasn't made by the current producers, a post on the Duet forums could be an idea.
(dc42 was an Ormerod 1 owner back in the day, and is an all-round helpful chap in my experience. Your original post may yield better results than can be provided here smiling smiley Although saying that, he does pop his head in here occasionally)
Re: Hotend temperature and heating issue
January 03, 2019 12:47PM
I re-checked everything, including the resistors value. They are 1k. I tried to force the values with M305, not better.
When I require the hotend to heat say to 190°C, the read and displayed temperature raises from 40°C (the "cold" temperature of the hotend is 17°C, read with a laser thermometer) up to 195°C in less than 10s whilst the actual temperature of the hotend raises up to 20°C. The orange led on the IR board switches on until the sensed temperature reaches 190°C, the fan starts when the displayed temperature is over 45/50°C. I tried to remove the heating cartridge from the hotend, it becomes quickly very hot and red, so I assume it does work.

I do think that the analog port on the Atmel where the sensor is connected is dead. Is there any other port I could connect the sensor, the one for a second sensor for example ? Then I could either "swap" P1 and P2, I think I've seen some G code to do that, or configure Slic3r to generate G-code for P2.
Re: Hotend temperature and heating issue
January 04, 2019 03:19AM
Suggestions:

1. Send M305 P1 without parameters. Check that the reported values are the correct ones as set in config.g.

2. To rule out a problem with the hot end fan/IR board, try connecting the 100k resistor directly to the Duet, with the cable from the hot end disconnected. You could also try some other resistor values, for example 10k and 1k. If those resistors give the wrong readings then it confirms a problem with the Duet, most likely with the processor.

There are several temperature sense pins on the expansion connector that you could use instead. You would need to connect a 4k7 resistor between the pin and +3.3V.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Hotend temperature and heating issue
January 04, 2019 04:00AM
Hi David,

Quote
dc42
1. Send M305 P1 without parameters. Check that the reported values are the correct ones as set in config.g.
Already done, the reported values are the correct ones.

Quote
dc42
2. To rule out a problem with the hot end fan/IR board, try connecting the 100k resistor directly to the Duet, with the cable from the hot end disconnected. You could also try some other resistor values, for example 10k and 1k. If those resistors give the wrong readings then it confirms a problem with the Duet, most likely with the processor.
Already done, with the 100k resistor connected in place of the thermistor to check the loom, then directly to the Duet. I also tried with various resistor values and checked against some resistance/temperature table I found in the troubleshooting documentation, the reported temperatures are always odd.

Quote
dc42
There are several temperature sense pins on the expansion connector that you could use instead. You would need to connect a 4k7 resistor between the pin and +3.3V.
Can you tell me which pin(s) I can use, please ? Regarding the 4k7 resistor, I suppose it is a pull-up one ?

Thanks
Patrice
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