I appear to have fried my hotend's heater resistor.

I appear to have fried my hotend’s heater resistor. I really don’t know why that happened, but I didn’t do a great job in my first build, so I’ll accept it for what it is. My printer is a RepRapPro Mendel, and it looks like I’m getting infinite resistance across that element.

Before I tear everything apart, is there any other troubleshooting I should try?

Also, I know it is a 6R8 resistor. How exactly do I identify the correct replacement part? Is it 5W dissipation?

If it’s a RepRapPro kit, ask them what they use. If it’s a new printer, they could likely send you another one. Also, I believe they’re designed for 12v, not 24v, so if you put 24v through it, a lot more power will flow through it and blow it out.

@ThantiK I’ve already contacted them and am waiting for a response.

The board is a Melzi V2 running Marlin, and the resistor is connected straight to the board. The board’s on https://github.com/mosfet/melzi . The printer is too: https://github.com/reprappro/Mendel.

I feel really stupid not being able to answer this question for myself - is that source material at all useful for answering this?

I have burnt three! of the RepRapPros resistors during 1 year of printing and I know of other that have burnt those resistors as well so your problem is not unheard of. I have now limit the max effect (in software) since I only printing PLA on that printer. Just limit max PID out for the extruder.

Good advice, David.

Do you know the exact specs of the resistor so I can order a replacement? I only know the 6R8 number, plus the <=5.1mm diameter and 12mm length.

I think it is “Vishay RWM5” 6R8 = 6.8 Ohm, however not totally sure. I do know that the resistors used is having a larger diameter in spec sheets than in real world. (Some of the resistors you need to throw away because of uneven thickness or because the body is bent). Not sure where the cheapest source is. I have ordered from http://www.electronic-things.de.