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Heated Resistor Problem

Posted by PatrickT 
Heated Resistor Problem
January 26, 2014 07:10AM
This all started yesterday when I was changing filament colour (from white to gold) and the gold jammed up the hot end. In the end, I had to take most of the hot end apart to unblock it however the real issue came after this.

Having put the hot end mostly back together, but not attaching it the the x-carriage yet, I tried to heat it up in order to run some filament through to check that it was really unblocked. Unfortunately, the hot end did not heat up.

I've checked that the thermistor is working by heating with a hair drier and it does register temperature change.

The upshot is, that I think somehow my heated resister has died: there is a voltage across the legs when it is set to heat up and when the printer is off, the circuit does not appear to be closed (i.e. open circuit across the legs when disconnected). Also, when I set the temperature from Pronterface, the red light on the Melzi controller board stops flashing and turns solid – I think this is bad.

Has anyone else had this issue before and will I need to replace my heated resistor? Also, does anyone have any idea as to how this could have happened?
Re: Heated Resistor Problem
January 26, 2014 08:24AM
It might be that the heating resistor died before the new filament jammed, and actually being the cause for this.
As you described, the resistor is interrupted, but there is no point in your story indicated that this might happened during the repair or the tests.
It is possible for the resistor to die, even if mounted correctly. Moreover, if you scratched the enamel when inserted it in the heating block, then it may die prematurely. This is because if scratched, it might happen that part of the resisting coil will be short-circuited, the rest of the resistor will be overloaded and is more prone to burn and interrupt.
Measure it once again, if broken, take it out carefully, see if it might have been damaged as said (just for getting the lesson learned) and, yes, you should probably replace it.
Re: Heated Resistor Problem
January 26, 2014 09:56AM
Thanks for the swift reply.

Sorry I neglected to mention this but the resistor actually died after unblocking as I heated it up a few times during the unblocking process. I’m not exactly sure when it stopped working but it was some time between taking the brass union of the Bowden tube out of the aluminium heat sink block (which is there the blockage turned out to be) and screwing it back in again.

I’ve tested and tried heating up again and still nothing so it looks like I will have to get a new one. I’m thinking of going for the updated ‘heater cartridge’ from RepRapPro on eMakerShop.

I’ve also taken the resistor out of the heater block (having to use more force than I excepted) and found quite a bit of the enamel has worn away somehow (see attached). My best guess is that when I was unblocking, some of the aluminium foil (which I had wrapped round the resistor to make it fit more snugly) dislodged and shorted part of the resistor.

Thanks once again for helping to confirm this fault,

open | download - Resistor_small.JPG (401.8 KB)
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