Problem with thermistors

chojn1 · 19 May 2017, 23:42

I got my printer built and working well for the last 2 weeks.
Unfortunately, starting up this morning, all the temperature readings on the heaters and bed thermistors are stuck at -273.1c on the panel due. CPU temp is till correct. All motor functions are normal.
The web control just show error as the current tempts.

Clicking on the bed link gives me:

Error: Temperature reading fault on heater 0: sensor open circuit.

Clicking on the heater link gives me:

Heater Fault
Error: A heater fault has occurred on this particular heater.
Please turn off your machine and check your wiring for loose connections.

I've tried changing out the wiring, the thermistors, and the bed heater.
I've also tried a reset and reinstalling firmware (version 1.18.1) to no avail.

Any help on what I should try next?
Thanks,
CJ

Sniffle · 19 May 2017, 23:50

I just had this happen as well,

you most likely had a short between the thermistor and your heater wire on the hotend(that tends to be what causes it) and blew your VSSA fuse.

you can search for VSSA in the forums as its happened to multiple people, to see how to diagnose it if that is the case as well as how to fix it, if you dont have the capabilities to SMD solder, there is a work around, but still requires soldering, you'll find it with your search and if i am able i will post some links.

chojn1 · 20 May 2017, 00:37

Thanks Sniffle,
That appears to be the problem.
I don't have the capability to SMD solder, so I am trying to find that work around.
CJ

Sniffle · 20 May 2017, 23:36

https://www.duet3d.com/forum/thread.php?id=247#p2462

This is the fix/workaround i used. you will need a .25A fuse. about the only place to find them is on amazon. I went to my local automotive supplier(O'reilly auto) and picked up a tube fuse holder. and soldered that inline as per the link and then added the fuse when it came in and she powered up like a champ and if it ever blows again due to a wierd short, i can just swap in a new one.

dc42 · 21 May 2017, 12:38

I intend to document how to retrofit a self-resetting polyfuse as implemented on the new 1.02 PCB revision, but it may be several days before I can do this.

chojn1 · 21 May 2017, 13:03

Thanks David, can't wait for the info.
In the mean time, as per Sniffle, I have ordered glass fuse holders and some 250mA fast acting fuses from Amazon.
Looking at the board this morning, I am thinking that I could just crimp the two wires of the fuse holder and plug one into the E1 thermistor VSSA pin and the other to a ground pin of the expansion header. Would that work as a temporary fix and avoid altering the board?

Thanks again, and thanks for the VSSA fuse. I think I would have fried the board by now without it. Though, I think you should not make us feel too over-confident about not being able to destroy the board. We can do it!
CJ

chojn1 · 23 May 2017, 20:21

Just a follow up on this thread,

I received the fuse and holder from Amazon today.
Crimped the two wires of the holder to a two pin dupont connector plug.
Plugged it into pins 40 and 42 on the expansion header and my machine is alive again.

Took less than 2 minutes and 2 bucks, no soldering or modification of the original board.
CJ

njjn2020 · 24 May 2017, 05:57

@dc42:

I intend to document how to retrofit a self-resetting polyfuse as implemented on the new 1.02 PCB revision, but it may be several days before I can do this.

David, what is causing this issue? thermistor? than i would like to protect my DuetWiFi board from failure and solder in a self -recovering fuse in thermistor wiring.
What voltage \ amps (or wattage) fuse should be used?

or it is faulty hot end?

thanks!

dc42 · 24 May 2017, 21:28

The fuse will only blow if you get a short between the thermistor wire that is connected to VSSA and something else, typically a fan or heater wire that is carrying 12V or 24V. One possible cause is a short from the thermistor wire to the hot end metalwork (which happens very easily when using small wire-ended thermistors) along with a short in the heater cartridge between the element and the casing.

SpeedyDad · 15 Aug 2017, 17:46

@dc42:

I intend to document how to retrofit a self-resetting polyfuse as implemented on the new 1.02 PCB revision, but it may be several days before I can do this.

Was the retrofit documented? Mine is doing the same thing.

dc42 · 15 Aug 2017, 18:12

@SpeedyDad:

@dc42:

I intend to document how to retrofit a self-resetting polyfuse as implemented on the new 1.02 PCB revision, but it may be several days before I can do this.

Was the retrofit documented? Mine is doing the same thing.

https://duet3d.com/wiki/Connector_and_spare_part_numbers#VSSA_fuse