Bed not heating anymore.
First time i've got a problem with the minion (around 220h printing time)
Heater heater_bed not heating at expected rate
See the 'verify_heater' section in docs/Config_Reference.md
for the parameters that control this check.
Once the underlying issue is corrected, use the
"FIRMWARE_RESTART" command to reset the firmware, reload the
config, and restart the host software.
Printer is shutdown
Searched a bit here on the discord and came across a few people with the same problem.
On my first overall view the cables look fine and not exposed or broken, nor any wear on them.
Tomorrow I will open the case if that will be suggested here. I must buy a multimeter probably, I loaned one when building the minion but it aint here anymore.
It does not heat at all anymore, it goes up to 100% but the celcius stays the same, after around 20 seconds I get the alarm.
Any thoughts?
25 Replies
if the wiring looks good, you probably blew the thermal fuse
optimistic-goldOP•2y ago
It happened mid print, is that possible by my wrongdoing or is it just a thing that can happen, randomly.
it happens when the bed gets hotter than the thermal fuse is rated for
optimistic-goldOP•2y ago
I was printing with the bed on 65c
either:
1) you wiring connection is bad
2) your SSR failed open
3) your thermal fuse blew
It has to be one of those - but you will need a multi-meter to verify
optimistic-goldOP•2y ago
edit: i will buy multimeter now to test continuity in the fuse
optimistic-goldOP•2y ago
I dont have an ssr, the wires look alright to me except one piece is black/dirty. How can I check the thermal fuse?
use your multi-meter and check resistance of the white wires. If you have infinite resistance that means there is a broken connection (and most likely your fuse blew).
optimistic-goldOP•2y ago
optimistic-goldOP•2y ago
Looks good to me? With continuity I also get a beep
Am not sure what happened, but I tried again heating it up and... it heats up again... 
what could be the cause of this? I have not changed anything, and I tested 20 times before I took the plate off the printer
what could be the cause of this? I have not changed anything, and I tested 20 times before I took the plate off the printeroptimistic-goldOP•2y ago
If you are using a 24V heater, the fault could be anywhere between PSU and the bed.
I would double check all wires for continuity (while flexing the cable) and loose crimp terminals (on Octopus or PSU)
optimistic-goldOP•2y ago
I checked stretching the cables when I removed the bed, I couldnt replicate the alarm again. All crimps were tight on the terminals. I will simply start a longer print for now, and see if it happens again. Thanks for help
Imma have to run by the cables again and will do what you suggested Flo, I printed 9 days again but now I run into the same problem.
Did you use good quality multi-strand wiring? Do you have proper cable strain relief?
optimistic-goldOP•2y ago
Its a standard minion that came with the cables, the strain relief im not sure, it does slide on the extrusion abit but it never will be fully stretched
optimistic-goldOP•2y ago
Oke, checked the cables for continuity and when I do the thermistor one I get
optimistic-goldOP•2y ago
When I check with the multimeter on the extruder thermistor, this does not happen. I did a hairdryer test before blowing on the heater pad and it registered a higher temperature... wich leads me to believe the thermistor is fine?
You probably shorted the wires when checking causing the thermistor to read a really high value and cause a shutdown. You don't want to check continuity while things are powered on
optimistic-goldOP•2y ago
Right, didnt know that. It shows 1.5v, no beep
optimistic-goldOP•2y ago
Not sure what that v means, but not 1.5 either anymore.
optimistic-goldOP•2y ago
alright, measured it at 112.5k Ohm. Followed prusa website multimeter usage ;p
optimistic-goldOP•2y ago
I can get the thermistor register heat when I blow air on it, so that must be working. I have continuity on the bed heater cables. I dont know what my next step would be. Before I was debating ordering thermistors, but it seems to be working.
then you need to start tracing back from the bed. Is the SSR supplying power? Is the MCU supplying power? Is the PSU supplying power?
optimistic-goldOP•2y ago
I think I got the problem. A fuse is broken on the board. No idea why though?
optimistic-goldOP•2y ago
The fuse still has continuity though
In any case I will replace it. I measured the volts coming from the psu and all is 24v.
Measured the volts coming from the mcu to the bed is 0. To the extruder heater 24v
Replacing the fuse worked, it heats up again!