Error on Thermistors

weput

Hello guys

I'm writting because im stuck. Out of the blue, both termistors (bed and hotend) started to fluctuate its reading from 20000 C° to -5C° or so...

naturally i checked all conections etc... and the system kept the odd behavior.

... so thinking it was a firmware issue, i factory reset and reinstall the latest firmware etc... and it stop fluctuating but now just stays both temps are at 2000C°. (like if the thermistors are disconnected).

Please advice.

a little strange with the fluctuations, but i suppose being a self resettable fuse its possible it goes a little wonky before failing.

anyways, take a look over at this thread while you wait for the pros to chime in: https://forum.duet3d.com/topic/15048/heater-0-and-heater-1-reading-2000-c/2

weput

@bearer said in Error on Thermistors:

anyways

I forgot to add this:

https://youtu.be/5d328Wj1e_o

This is the behavior i have now. What pisses me off is that it was working fine.

if you say the wiring is good and the duet says the sensors are disconnected that leaves the fuse; the thread i linked to will walk you through the testing

weput

if i desconect the sensors, temp stays at -273.1C

This is the output code i get from the troubleshooting.

4/3/2020, 10:03:14 PM 	M950 h1
Heater 1 pin e0heat frequency 250Hz, sensor 1
4/3/2020, 10:03:09 PM 	M950 h0
Heater 0 pin bedheat frequency 250Hz, sensor 0
4/3/2020, 10:02:59 PM 	M308 s1
Sensor 1 type Thermistor using pin e0temp, reading -273.1, last error: sensor open circuit, T:100000.0 B:4138.0 C:0.00e+0 R:4700.0 L:0 H:0
4/3/2020, 10:02:51 PM 	M308 s0
Sensor 0 type Thermistor using pin bedtemp, reading -273.1, last error: sensor open circuit, T:100000.0 B:4138.0 C:0.00e+0 R:4700.0 L:0 H:0
4/3/2020, 10:02:34 PM 	m115
FIRMWARE_NAME: RepRapFirmware for Duet 2 WiFi/Ethernet FIRMWARE_VERSION: 3.0 ELECTRONICS: Duet WiFi 1.0 or 1.01 FIRMWARE_DATE: 2020-01-03b3

weput

I was running 2.05 when the issue started..

did a factory restore and loaded 3.0

Danal

3.0 is a little unique, being a HUGE change from 2 to 3, and being a "dot zero". I'd go ahead and go to 3.01 RC5 or RC6. Or stick with 2.0.5. I just wouldn't run 3.zero.

Probably nothing to do with your problem, since it started before the upgrade... it will avoid lots of other problems!

weput

same fluctuating behavior.. (see video https://www.youtube.com/watch?v=5d328Wj1e_o)

4/3/2020, 10:39:12 PM 	m115
FIRMWARE_NAME: RepRapFirmware for Duet 2 WiFi/Ethernet FIRMWARE_VERSION: 3.01-RC6 ELECTRONICS: Duet WiFi 1.0 or 1.01 FIRMWARE_DATE: 2020-04-03b3

if i pull the sensors off they stay at -273.

my config

; Heaters
M308 S0 P"bedtemp" Y"thermistor" T100000 B4138         ; configure sensor 0 as thermistor on pin bedtemp
M950 H0 C"bedheat" T0                                  ; create bed heater output on bedheat and map it to sensor 0
M143 H0 S120                                           ; set temperature limit for heater 0 to 120C
M307 H0 B1 S1.00                                       ; enable bang-bang mode for the bed heater and set PWM limit
M140 H0                                                ; map heated bed to heater 0
M308 S1 P"e0temp" Y"thermistor" T100000 B4725 C7.06e-8 ; configure sensor 1 as thermistor on pin e0temp
M950 H1 C"e0heat" T1                                   ; create nozzle heater output on e0heat and map it to sensor 1
M143 H1 S305                                           ; set temperature limit for heater 1 to 305C
M307 H1 B0 S1.00                                       ; disable bang-bang mode for heater  and set PWM limit

weput

@Danal said in Error on Thermistors:

it

ok

not sure why i went this route; but downgraded back to 2.05.1 before pulling out the multimeter. Definitely a hardware issue.

I shorted one VSAA pin to ground (while powered from USB) to ground and intermediately got a reading on both thermistors.

Dunno how this happened; but before what im reporting i found the printer halted with thermistor error:

must had shorted something while replacing the thermistor...

anyways, with this covid-19 lockdown; im not gonna be able to replace the fuse

@weput said in Error on Thermistors:

I shorted one VSAA pin to ground (while powered from USB) to ground and intermediately got a reading on both thermistors

thats more or less the part I was hoping you'd go for

@weput said in Error on Thermistors:

anyways, with this covid-19 lockdown; im not gonna be able to replace the fuse

you could run with the short, but you run the risk of more damage if something shorts again; or if you have any low value fuse you could use that in a similar manor as the short as a temporary or permanent bandaid.

(edit: if you're tempted to operate the printer with a temporary short across the VSSA fuse use the thinnest single strand of wire you can find - super flexible silicone wire for instance has an OD of 0.08mm for a single strand and it will effectively act as a low value fuse) nope, still carries too much current

dc42

@weput said in Error on Thermistors:

@Danal said in Error on Thermistors:

it

ok

not sure why i went this route; but downgraded back to 2.05.1 before pulling out the multimeter. Definitely a hardware issue.

I shorted one VSAA pin to ground (while powered from USB) to ground and intermediately got a reading on both thermistors.

Dunno how this happened; but before what im reporting i found the printer halted with thermistor error:

must had shorted something while replacing the thermistor...

anyways, with this covid-19 lockdown; im not gonna be able to replace the fuse

It sounds to me that you may have a lot of leakage between one of the thermistor wires and VSSA. That leakage is likely to get worse and damage something. The VSSA resettable fuse protects against that kind of damage.

Try disconnecting one thermistor at a time from the Duet, then see if you get a stable reading from the other one without shorting VSSA to ground.

weput

@dc42
I did that... No luck.

Duet WiFi 1.0 or 1.01

Fuse is blown.

weput

@bearer
I'm tempted to do that.

I placed my cheap analog multimeter in ohmimeter between vssa and gnd and got a reading. (120 or 1.2 kilo ohms... Can't be sure anymore)

Digital states open...

Unfortunately I don't have much at hand to fix this.

@weput said in Error on Thermistors:

I'm tempted to do that.

if the unstable reading is persisting, then as dc42 suggest its not adviceable.

Otherwise any 100mA or smaller fast acting fuse will provide some protection if wired between VSSA and GND.

weput

@bearer that's the thing...

It's not going to be easy to find a fuse that small with the Lockdown.

Its your call, the fuse did blow because of a short on your thermistor - if it happens again without a fuse something else will blow.

weput

I'll make a permanent short and check the reading for like 10 mins...

I don't want to blow the board but I assume is better this than setting one of those old 8 bits on.

dc42

What hardware revision Duet is it?

weput

@dc42 said in Error on Thermistors:

?

This is one of those preorders boards... (numbered 138) preorder group 2.

so i assume hardware ver1.0

dc42

@weput said in Error on Thermistors:

@dc42 said in Error on Thermistors:

?

This is one of those preorders boards... (numbered 138) preorder group 2.

so i assume hardware ver1.0

Thanks. See https://duet3d.dozuki.com/Wiki/Connector_and_spare_part_numbers#Section_VSSA_fuse.