Bad Heatbed problem

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Posts: 8
Joined: Tue Apr 02, 2013 10:26 am

Bad Heatbed problem

Post by titchy »

Hi, after few teething problems and frustrating moments, i have had a Felix 1.5 up and running for about a month.
I had a faulty thermister in the hot end on delivery, and i melted the thread out on the plastic part between the two aluminum parts of the extruder head!
Thanks for Guillaume for your understanding and replacement part, appreciated!
No idea the real temperature it melted at, but scares me abit about printing ABS and and other material i can get my hands on.

Frustration aside, Im impressed with the prints, i have slight z wobble but nothing i cant fix by tinkering.

Now i have a bad electronics problem, the heat bed doesnt warm up.
I have separated all the resistors and wires, and traced the fault back to the electronics board output for the heat bed.
Im guessing this the the mosfet that gets very hot, which is already mentioned in other posts (that i didnt read in time).
The output from the screw terminals (+ AND - FOR HEAT BED WIRES), when the resistors are disconnected measures 0v, and when i turn the heat bed on through the manual control in the software,the voltage occasionally jumps up to 4v or 12v but no heat in the resistor(s) so i suspect very little current is being drawn.
I assume this should be solid stable 12v? or does is rise?

Im currently printing PLA on blue tape (cant afford downtime) but need to print ABS soon...

Anyone know if this is an easy fix with a new mosfet and bigger heatsink?

Is this the reason for the Felix 2.0 upgrade to include the electronics (for heat bed) and the new heatbed foil heater sticker?

Does the 2.0 allow for higher temperatures on the heatbed for better ABS prints?


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Joined: Fri Mar 08, 2013 1:15 pm
Location: Finland

Post by kimmoli »

While assembling the printer, i did notice that ramps board (tjsp) had these screw terminals, and their pins were cut post-soldering. When tightening cable to one, i noticed that the solder joint was broken - the terminal was rotating lots more than other ones, so i decided to resolder all the pins of those screw terminals and so far all ok.

Hope this helps?

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Joined: Wed Aug 15, 2012 1:13 am

Post by Lioric »

The temps are closed loop controlled, via pwm (that is why the occasionally 4 ~ 12v you see) , if the thermistor is bad, then the mosfet won't turn on enough time to heat the bed. The occasional voltage on the mosfet means that is working

First review if the bed thermistor is working correctly, and reflash the firmware to trace the issue from a clean state

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Joined: Tue Apr 02, 2013 10:26 am

Post by titchy »

I resoldered the screw terminals on the pcb, then setup a new pc and reflashed the Arduino and i have a working heatbed again!
Thanks Kimmoli and Lioric!

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