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Newbie with a problem - can't get bed to heat up at all sad smiley

Posted by MrCrispi 
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MrCrispi
Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 09:34AM
Just finished building and all looking very hopeful on the commissioning front EXCEPT I can't get the bed to warm up at all sad smiley
If I send an M105 code in a monitor window I get: ok T:27.7 B:-39.7 I am presuming the t is for hot end temp and the b is for bed temp? I therefore guessed this mean't my bed thermistor was not connected (dodgy crimp or similar) but rechecked and finally soldered the connection to be sure. I've got no error messages showing and I can move the head in all three axis, heat up and cool down hot end no problem, just nothing happening on the bed. I get the same message with or without the thermistor or ribbon cable connected and am now out of ideas,other than sourcing a new thermistor or finding some way to (very temporarily) override the thermistor so I can check that the ribbon cable works and the bed will (some day) heat up - can anyone out there help please?
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rayhicks
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 09:45AM
I think that you may have problem on your duet - the temperature should show as absolute zero if there's an open circuit - if yours isn't changing when you remove the thermistor then the resistance isn't being read properly.

I think someone had a similar issue, and (I think) dc42 remapped one of the pins - using a different pin for thermistor input may help you to get to the bottom of your problem too
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MrCrispi
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 09:53AM
Thanks for the superfast response - it is much appreciated...I will now see if I can hunt down what pin to remap to before trying something more drastic...meantime if anyone has more detail on what I need to do that would be great
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rayhicks
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 10:07AM
if you do need to reassign a pin it isn't trivial unfortunately - the thread I mentioned is this one [forums.reprap.org] where the pin used for the z-probe didn't work, dc42 modified the firmware to use a different pin as a test.

Cheers
Ray
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reprappro
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 10:30AM
Temporarily override the bed thermistor with a 10k resistor - this should test if there's a problem with the board.

You can test the bed thermistor by unplugging the ribbon cable, putting a couple of pin headers in the centre of the ribbon cable, and checking the resistance.

You can also check it on the board (if you don't have pin headers): with the ribbon cable plugged in, and power off, measure the resistance between the two vias in the top left of the Duet, marked 'BED_TEMP' (this is an extra connection for the bed thermistor). It should be around 1.9k ohms. Remove the ribbon cable and test again, it should be around 2.3k ohms.

Ian
RepRapPro tech support
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Radian
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 11:11AM
Hold on, is the bed actually being energised? I can't tell from reading the posts so far - it all seems to be about not being able to monitor the temperature. Simple question - do the bed LED's illuminate?

RS Components Reprap Ormerod No. 481
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MrCrispi
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 11:13AM
Measured "vias" as suggested - With ribbon cable in place, negligible resistance (2 ohms) with ribbon removed 1.1k ohms - thoughts?
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rayhicks
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 11:32AM
is there a short in the cable? have you got your wire crossed? It sounds like the heater resistance is connected to the wires that should go to teh thermistor (the heater element has a resistance of around 1.2ohms...

check that you have the right splits in the bed end of the cable to start with,

Ray
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reprappro
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 11:34AM
The bed thermistor is shorting out! Or you've put the cable together incorrectly, and the middle two wires are not the thermistor, or it's plugged into the board incorrectly.

Ian
RepRapPro tech support

Edited 1 time(s). Last edit at 01/14/2014 11:35AM by reprappro.
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GregL
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 11:59AM
@Ian
measure the resistance between the two vias in the top left of the Duet, marked 'BED_TEMP'

I have an anxiety that the battery in the multimeter means that there is a potential problem dabbing its probes on the circuit board; could it do damage? is there a right way and a wrong way to apply the probes?

Greg

Ormerod #17
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MrCrispi
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 12:15PM
No sign of life on the bed at all - didn't even realise there were led's smiling smiley will further investigate wiring...
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MrCrispi
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 12:22PM
As far as I can tell the cable looks spot on...the split is 12 + 2 +12 as per instructions and all crimps look secure...always difficult to be sure on a ribbon cable I suppose, but if the ribbon cable were the problem wouldn't you expect there to be some difference in what was showing with and without the cable in place? The core message I get on sending an M105 code is identical with or without the ribbon cable...this is all I have to go on as a symptom as there is no sign of life in the bed at all. Guess I could make up a new ribbon cable, but not sure at this stage why that is likely to make it work...
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reprappro
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 12:27PM
It's more likely that the thermistor is shorting out somewhere, probably at the bed end, or the connectors. You're going to have to find the fault, unfortunately.

@GregL: You can only test resistances with power off. No, a multimeter won't damage the board, and the thermistor has no polarity, so there's not even a wrong way around to use the probes!

Ian
RepRapPro tech support
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Radian
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 12:29PM
Quote
MrCrispi
No sign of life on the bed at all - didn't even realise there were led's smiling smiley will further investigate wiring...

So no power to the bed. There's also a LED next to the transistor that switches power to the bed. It's tucked in between the transistor and the ribbon cable connector on the Duet PCB. It should light when you set a bed temperature above ambient. If this lights and the ones on the bed don't it's definately the ribbon that's wrong.

Er, am I missing something - does the bed transistor not get switched on if the temp. readings are out of whack? In which case ignore my bad.

Edited 1 time(s). Last edit at 01/14/2014 12:31PM by Radian.

RS Components Reprap Ormerod No. 481
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dc42
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 12:31PM
If the temperature reading is below -30C or above +300C then the firmware treats that as an error and won't allow the heaters to come on. If your bed reading is -39.7 then this explains why the bed heater won't come on.

I'm not clear as to where you unplugged the ribbon cable. If you unplug the ribbon cable at the Duet end, what M105 reading do you get?


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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MrCrispi
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 12:37PM
Thanks for all the help radian smiling smiley stick with me! When powered up I only have 3 LEDs showing on the duet board - two come on whenever the USB port is connected and the third (half way down between the USB port and the bottom of the board) comes on when the ATX is powered up - nothing else lit up at any time...
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MrCrispi
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 12:42PM
I unplugged the duet end of the ribbon cable when taking the readings...just unplugged the two cables on the bed end and remeasured to cross-check- 1.1k ohm unplugged just as before
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TMD_RS436
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 01:11PM
Quote
rayhicks
I think that you may have problem on your duet - the temperature should show as absolute zero if there's an open circuit - if yours isn't changing when you remove the thermistor then the resistance isn't being read properly.

I think someone had a similar issue, and (I think) dc42 remapped one of the pins - using a different pin for thermistor input may help you to get to the bottom of your problem too

Na, dc remapped the pin for the Z sensor due to the pin on my board was shorted to ground.

Paul

RS Ormerod No 436
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TMD_RS436
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 01:14PM
Quote
MrCrispi
Thanks for all the help radian smiling smiley stick with me! When powered up I only have 3 LEDs showing on the duet board - two come on whenever the USB port is connected and the third (half way down between the USB port and the bottom of the board) comes on when the ATX is powered up - nothing else lit up at any time...

That other LED is if I recall for the Y Axis Microswitch which will go out when the switch is pushed.

Paul.

RS Ormerod No 436
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Radian
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 01:20PM
Bed heater LED circled on Duet PCB

(note that this one has green terminal blocks instead of pin headers like on yours)

I also scribbled where you could connect a 10K resistor (if you had one) to bypass the thermistor . You would unplug the ribbon to remove the whole bed from the equation, and try fooling Duet to power the bed by pretending to have a reasonable temperature as per Ian's suggestion. If the heater LED lit up when you did this it would isolate the problem to be in the ribbon cable/bed.

RS Components Reprap Ormerod No. 481
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MrCrispi
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 01:21PM
And it does - that bit is fine at least (silver linings and all that!) smiling smiley
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dmould
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 14, 2014 01:31PM
It really does sound like either your ribbon cable is incorrect at one end or the other (ensure it is not plugged in one pin out on the Duet, there should be no pins visible at either end of the ribbon plug), or you have a short across your thermistor. With the ribbon cable completely unplugged at the Duet end, you should see a temperature reading of -273.1 If you do, then it is definitely ribbon incorrect or shorted/bad thermistor.
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MrCrispi
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 16, 2014 05:49AM
Nailed it - faulty thermistor! Many thanks to all who have helped me...particularly to @Radian for the picture showing where to apply a10k resistor to override the thermistor - above and beyond and really appreciated. As soon as I over-rode the thermistor the bed sprang to life (so ribbon cable was fine all along!) and I could feel it warming nicely - will now source new thermistor and I think I'm good to go and actually print something smiling smiley

The gratifying part of this "bump in the road" for me has been the speed with which people have piled in with suggestions on this forum....I hope in time I'll be able to offer help back perhaps...
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Radian
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 16, 2014 05:58AM
Glad you found the problem. I'm sure support at reprappro dot com would help you with the wonky thermistor smiling smiley

RS Components Reprap Ormerod No. 481
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dc42
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 16, 2014 06:26AM
Are you sure it really is the thermistor at fault, and not the 2-pin plug/socket under the bed and the associated crimp connections?


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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rayhicks
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 16, 2014 06:30AM
dc42 has a good point - now that you know a resistor is sensed properly at the board, try using it to replace the thermistor at the other end of the cable, and make sure you still get the same response
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MrCrispi
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 16, 2014 07:25AM
Good catch - poor deductive logic on my part, but have just fitted a new thermistor and voila - all good smiling smiley
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reprappro
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 16, 2014 07:52AM
MrCrispi: What thermistor have you used? You need a 10k thermistor, and if it doesn't have the same beta value (3988) as ours, your temperatures will be inaccurate.
Our bed thermistor: [uk.farnell.com]

Ian
RepRapPro tech support
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MrCrispi
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 16, 2014 07:57AM
I used an RS 10k one - will that be OK?
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reprappro
Re: Newbie with a problem - can't get bed to heat up at all sad smiley
January 16, 2014 09:13AM
I don't know! What is it's beta value? Link to product?

Ian
RepRapPro tech support
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