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Dead hot end therminster?

Posted by Pyro 
Dead hot end therminster?
November 02, 2014 07:50AM
Hey guys
I've finally finished assembling my Ormerod 2. Plugged it in for comissioning and found one of the thermisters is unresponsive.
The M105 command is giving a read out of
T:B 20.9

I took the hot end thermister out for a continuity test and that seems to be failing. I am guessing that this is a pretty good indicator that the thermister is dead.
Re: Dead hot end therminster?
November 02, 2014 11:56AM
Either your config.g file on the SD card is incomplete (in particular it is missing an M563 command to define the hot end), or config.g is not being executed at startup.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Dead hot end therminster?
November 02, 2014 12:27PM
Quote
dc42
Either your config.g file on the SD card is incomplete (in particular it is missing an M563 command to define the hot end), or config.g is not being executed at startup.

But it was displaying this when I had no SD card in and was running off of the arduino interface only. Also what about the continuity test?
I'll have a check of my SD card contents and see if it is missing the config file command.
Re: Dead hot end therminster?
November 02, 2014 02:32PM
Quote
Pyro
But it was displaying this when I had no SD card in and was running off of the arduino interface only.

That is entirely normal. If it doesn't read the M563 command from config.g for any reason (such as because the SD card is not inserted), then the hot end doesn't exist as far as the firmware is concerned, and no temperature will be read from it.

Quote
Pyro
Also what about the continuity test?

The resistance of the hot end thermistor is 100K or more at typical room temperatures, which is too high to register on a continuity tester. You should be able to measure it using the resistance range of a good multimeter.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Dead hot end therminster?
November 02, 2014 03:18PM
Well I tried my multimeter on a higher setting for the resistance and I am getting a reading! It doesn't seem dead after all!
I've checked the SD card for the config.g and it contains this line
M563 P1 D0 H1                       ; Define tool 1
So I think that command is in fact there. Any idea why it is not being executed?

Incidently, I removed the heat shrink wrapper fro a closer examination , would you know if replacing the transparent stuff with the black stuff is an acceptable substitute?
Re: Dead hot end therminster?
November 02, 2014 03:51PM
Quote
Pyro
So I think that command is in fact there. Any idea why it is not being executed?

That probably means that config.g is not being executed at all at startup. Another symptom is that if config.g has been executed, then after you send any command there should be an OK response (after any data that is sent back). If config.g is not executed, there is no OK response.

Try sending command M503 from the Arduino serial monitor. If you get back an error response, it means that the Duet can't read the SD card at all.

Quote
Pyro
Incidently, I removed the heat shrink wrapper fro a closer examination , would you know if replacing the transparent stuff with the black stuff is an acceptable substitute?

No, the black heatshrink won't take the high temperatures of the hot end.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Dead hot end therminster?
November 03, 2014 06:50AM
I've refitted the thermister and after running the M563 command everything seems to be working ok. I'll have a go at running the M503 command when I get back from work tonight to check the SD card out.

Thanks a lot for your pacients in this. I very much appreciate it.
Re: Dead hot end therminster?
November 03, 2014 07:38AM
Hi Pyro

I've updated the instructions to explain the 'T:B 20.9' problem, see: [reprappro.com]
Basically, it's a temperature fault, usually caused by a disconnected or short circuited thermistor, that causes the hot end to be disabled. Unfortunately, it also causes the hot end temperature to stop being displayed in Pronterface - the web interface does continue to display the reported temperature. We'll change this in the next firmware update.

Ian
RepRapPro tech support
Re: Dead hot end therminster?
November 03, 2014 08:02AM
Ian,

A missing reading after "T:" in response to M105 doesn't necessarily indicate a temperature fault. You also get this issue if no M563 command has been executed, for example because config.g was not processed, or there was no M563 command in config.g. Try commenting out the M563 command in config.g and you will see what I mean.

Edited 2 time(s). Last edit at 11/03/2014 08:03AM by dc42.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Dead hot end therminster?
November 03, 2014 08:22AM
Quote
Pyro
I've refitted the thermister and after running the M563 command everything seems to be working ok. I'll have a go at running the M503 command when I get back from work tonight to check the SD card out.

Thanks a lot for your pacients in this. I very much appreciate it.

Did you get some replacement high-temperature heat-shrink for the hotend thermistor? It is not safe to run without it because of the risk of the thermistor wires shorting to the aluminium heating block.

Dave
Re: Dead hot end therminster?
November 03, 2014 09:32AM
Quote
dc42
Ian, A missing reading after "T:" in response to M105 doesn't necessarily indicate a temperature fault. You also get this issue if no M563 command has been executed, for example because config.g was not processed, or there was no M563 command in config.g. Try commenting out the M563 command in config.g and you will see what I mean.

I put this up as an alternative explanation to the reasons you had listed. It's also the correct reason, in this case, indicating a temperature fault, with the thermistor and/or wiring being the issue. I agree that you get the same thing if config.g is not being read, or there's not an M563 in config.g, but this isn't born out, even by his initial description. You gave him an either/or choice, neither of which resolved the problem!

Ian
RepRapPro tech support

Edited 1 time(s). Last edit at 11/03/2014 09:33AM by droftarts.
Re: Dead hot end therminster?
November 03, 2014 10:28AM
Hi Dave.
I managed to get some shielding from a guy at work so thats sorted now.

Ian/dc42. I am not sure what solved the problem. I reconnected the thermister/hot end loom and executed the M563 command as it appeared in the config file and it seemed to work after that. Also it does look as if the SD card was bing red. I got the config listing returned and my other commands had "ok" at the start. I'll double check everything tonight though.
Re: Dead hot end therminster?
November 03, 2014 10:32AM
Pyro, I'm glad you got it working. Perhaps you had a wiring fault as Ian suggests.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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