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Duet aborted print due to heatbed heating failure

Posted by Brummie 
Duet aborted print due to heatbed heating failure
January 10, 2019 10:42AM
Hello,

i was surprised by an aborted printjob. Error message showed, that the heatbed is not heated any more.
I removed the wires from Duet and checked the resistance - heatbed seems to be ok.
So may be, the mosfet has died.

Is there a way to get the mosfet-signals out of the duet, so that I could attach a ssr?
Re: Duet aborted print due to heatbed heating failure
January 10, 2019 11:19AM
Well, one of the simple ways to deal with it might be to just use a different heater channel and an external MOSFET. There are several such on the expansion header (Diagram here: [duet3d.dozuki.com] )

I'd want to check first though. You seem to have a multimeter, so just check that you're getting voltage on the bed pin.

If you are not getting +Vin on the positive pin, then you have a different fault. (On the V1.04 boards, there is a fuse for the heated bed, I'd check that first.) The MOSFET switches the ground pin. If you do not have continuity to ground when the head bed LED is lit, then you have a failed MOSFET. You really should verify what the fault is before taking any remedial action.


MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts
Re: Duet aborted print due to heatbed heating failure
January 10, 2019 04:47PM
What exactly was the error message? Maybe there was a heating fault and the firmware turned the heater off deliberately. This can happen if you didn't run heater tuning.

It's almost unheard of for the bed heater MOSFET on a genuine Duet to fail.



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: Duet aborted print due to heatbed heating failure
January 11, 2019 12:23AM
Thank you both for your fast reply!

Quote

You seem to have a multimeter, so just check that you're getting voltage on the bed pin.
OK, i checked:
On powering board on, no voltage on heatbed pins.
Then I connected WebIF and turned heatbed on.
Stil no voltage on heatbed pins.
I checked with DC and AC settings.

by the way: it does not smell like rotten electronics

Quote

It's almost unheard of for the bed heater MOSFET on a genuine Duet to fail.
I very hope, that I have a genuine Duet. I paid the price for a genuine board.
The ID-Part of the board is this:


Rest of the board seems to work as expected.

Quote

This can happen if you didn't run heater tuning.
I did run heater tuning for both heatbed and hotend.
Errormessage was about 15° mismatch or so.

Quote

There are several such on the expansion header
Ok, thanks for the hint.
I found Heater3-Heater7 on expansion slot. I suppose, those pins are connected to the atmel chip directly.
I have a Fotek ssr-25 dd, which works from 3V on.
Can I connect that ssr directly to the expansion slot, or do I need some protection parts?

Edited 2 time(s). Last edit at 01/11/2019 12:54AM by Brummie.
Re: Duet aborted print due to heatbed heating failure
January 11, 2019 01:28AM
I extracted the board to make some photos from the mosfet.
Upside looks quite usual:


but bottom-side shows a "dirty" area. Looks and feels greasy


Heatbed was heavy used lately. I printed about 4kg ASA with 105°C nominal on a modified Ender-3. It's heatbed is not that powerfull, so that it consumed lots of power and for so stressed the mosfet.
Re: Duet aborted print due to heatbed heating failure
January 11, 2019 02:53AM
The MOSFET can take a lot of current without overheating. The bed heater current limit is determined by heating of the ground trace that runs along the edge of the board on both sides, and connects the MOSFET source terminal to the negative VIN terminal. That trace looks in good condition in your photo.

There is a red LED close to the MOSFET. Does it light up when you try to turn the bed heater on?



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: Duet aborted print due to heatbed heating failure
January 11, 2019 02:56AM
You can connect the control terminals of an SSR directly between one of the heater signals on the expansion connector and +3.3V. However the SSR-25DD is a very poor SSR and will get very hot when passing typical bed heater current.

If you are not using the E2 heater output, you can also connect the control terminals of an SSR to that.

Edited 1 time(s). Last edit at 01/11/2019 02:59AM by dc42.



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: Duet aborted print due to heatbed heating failure
January 11, 2019 03:10AM
PS I presume your Duet is out of warranty, but it can probably be repaired. Which country are you in?



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: Duet aborted print due to heatbed heating failure
January 11, 2019 03:26AM
Quote

There is a red LED close to the MOSFET. Does it light up when you try to turn the bed heater on?
Yes

Quote

However the SSR-25DD is a very poor SSR
Well, I ordered a silicone heater for 220V with about 500W - the ssr was intended for that use case.
It has a metal backplate so I wanted to mount it on some alu profiles.

Additionally I have a RP1A23D5 from Carlo Gavazzi and a SSR-D3805HK from Hoymk
Is any of those suited to drive a heatbed?

I didn't use E2 til now. Good idea. Thank you.

Quote

PS I presume your Duet is out of warranty, but it can probably be repaired. Which country are you in?
I live in germany.
Thank you for your support!
Re: Duet aborted print due to heatbed heating failure
January 11, 2019 07:28AM
Quote

I presume your Duet is out of warranty
What are the conditions of warranty?
I bought it at 04.08.17 from filafarm.de

... is the mosfet gone?
Re: Duet aborted print due to heatbed heating failure
January 11, 2019 12:39PM
FWIW, when I said to check for Vin at the bed heater, I did not mean across both terminals, I had meant just the Vin pin, with reference to the power supply ground. Then check the negative terminal for continuity to ground, but it appears that your board is older than a v1.04, so there's no Vin fuse on the bed heater circuit. It would have been nice if the problem were as simple as a blown fuse.


MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts
Re: Duet aborted print due to heatbed heating failure
January 11, 2019 12:54PM
Quote
Brummie
Quote

There is a red LED close to the MOSFET. Does it light up when you try to turn the bed heater on?
Yes

In that case, the bed heater mosfet is working. The LED measures the output from the mosfet. I suggest you check that the bed heater terminal screws on the Duet are tight, that the wires to the bed are sound, and that the bed itself hasn't gone open circuit.



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: Duet aborted print due to heatbed heating failure
January 12, 2019 02:35AM
Nature doesn't care about things, that should happen, or things that should not happen ...

When I was told to measure voltage of heatbed output, I measured impedance of heatbed to ensure, that there's no problem on the other side. Impedance of the heatbed was about 4 Ohm, which to me sounded somewhat reasonable, so I didn't grab deeper.

When I read, that the mosfet should be ok, I remembered, that my multimeter is a cheap one which is not capable of true rms ...
... but, I remembered, that I have a very tiny DSO.
So I powered the board by a laboratory power supply and connected one dso-channel to positive heatbed output and the other channel to the negative heatbed output channel.

I was very surprised, that the board consumed only about 90-100mA smiling smiley
(shown by the laboratory power supply)

This is the heatbed output in idle state:


When I turn heatbed heater on, the pwm-line turns into a straight line.
I have no idea, why the multimeter was not capable to measure any voltage.

Then I dismounted the heatbed. On Ender-3 the cable at the heatbed connector is supported by a plastic cable holder, which should prevent cable from breaking from the solder pad.
Well, the cabel was broken and in the endposition of the heatbed the broken cable touched the heater pad. That way I could measure an impedance.
After resoldering the cable I measured the impedance of the heatbed again and it showed 3 Ohm.
Not that far from previous result.

conclusion (for me): you can't even know without having checked every possible cause.

Thank you for your support!
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