Thermistor problem…
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Use a 100 to 250mA quick-blow fuse. A slow-blow fuse might not protect the PCB traces and vias,
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thanks i do have to say costumer support on a Sunday iyour just spoiling us you guys are on top of your costumer support game
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While I don't disagree a socketed fuse would be nice, you're actually fortunate that VSSA fuse is there at all. Had this been a wired Duet, Smoothieboard, any Makerbase board, and probably a few others that don't have analog ground protection you likely would have permanently damaged the board beyond reasonable repair.
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yes i do agree i am fortunate that a fuse was there
but all early boards came with reset fuse are old car fuse to protect some parts of the circuity
kind of shocked that we are now stepping backwards and not using them -
p.s ive now done a quick test power and thermistors plugged in only and it works again few think i may change over to the pt100 stop this from happening again
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As W3DRK says, the VSSA fuse is something that you won't find on any other board AFAIK. The reason for it is that there have been sporadic reports of the microcontroller on wired Duets getting fried. Other details of the failure suggested that a likely cause was a short from a heater output to a thermistor input. That's why I added the VSSA fuse. I thought that it might save perhaps 1 user in 1000 writing off their Duet WiFi. I am very surprised that it seems to be more like 1 user in 100.
I have already suggested that when we next revise the Duet WiFi PCB, we use a different fuse. If we do then it will still be SMD because of space and cost constraints, but it will be larger and have metal end caps, making it easier to replace.
The fuses that you get on some other control boards may not protect the PCB and the microcontroller from this type of short. The fuse I chose has a low current rating so that it blows quickly, and a resistance high enough to limit the current before it blows, so that the vias on the PCB can handle the surge and the ground voltage disturbance is kept at a safe value.
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To add to that, the only boards with blade fuses I have seen are there to limit the total current to high power elements of the board (heaters) while that may be useful, it would not have helped this sort of fault.
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understood and again thanks for the reply ok so adding a big chunky fuse is not viable and /or cost effective in the case of future development what about pin out hole so people can add there own fuse easily if the need arises
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Connecting an external 250 mA fuse between E1 thermistor VSSA pin and E0 stop GND pin as a substitute for F1 fuse solved my problem
Temperature readings now ok. Thanks again, AndreS and dc42!So just to clarify (so I don't do something stupid), you do the above with the hotend thermistor plugged in to E0. Correct?
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See https://duet3d.com/wiki/Connector_and_spare_part_numbers#VSSA_fuse for ways to get your Duet working after a VSSA fuse failure. How you wire the thermistor to the Duet is not affected by any of these methods.
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See https://duet3d.com/wiki/Connector_and_spare_part_numbers#VSSA_fuse for ways to get your Duet working after a VSSA fuse failure. How you wire the thermistor to the Duet is not affected by any of these methods.
Thanks!
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Got the fuse and wired it in. All is well.
