maxtemp triggered

Hi all! I've come up against a problem and I'm a little bit unsure how to rectify. The hotend is currently off as the MAXTEMP was triggered (somehow). It did it yesterday and I turned it all off and waited to see if it sorted itself out. It's now done it again after printing ok for about 10 mins. Could someone advise me how I reset the Maxtemp thing so I can test again?

I thought there may be a short somewhere but it's been printing fine until yesterday so it would be a new fault if so. I don't know what to test to check and searching on the forum hasn't been too fruitful, although there must be some threads on it somewhere! Any advice would be appreciated!

Thanks

I should probably add that the hotend is reading at 260 degrees or so in pronterface, but it's cold to the touch. Presumably that's an issue with the thermistor? It looks normal at the hotend, ie nothing touching, all wires covered up etc...

I'll continue playing with it whilst still open to suggestions of course!

Disconnect the thermistor from the Melzi and put a resistance meter across the two leads.
What resistance is the thermistor registering?

it's reading about 12k and the hotend was just showing 90 degrees prior to the maxtemp error again (I tried a print after disconnecting the thermistor before I saw your reply)

Thanks

Assuming your hot end came with a 100k thermistor and that it is currently cold, 12k seems on the low side.

I just checked again and it's 104k now. Maybe I got it wrong before! I'm not an avid multimeter user... I could swear I had it on the 20k parameter setting before!

I think I'll go over the pre-start electrical checks in the build manual next to make sure they all read correctly

It seems like an intermittent partial short across the thermistor. The only way I can imagine that could happen is if the insulation or heatshrink has burnt where the wires are bundled together. I would remove the tie wrap around the hot end and cut off the outer heatshrink to see if there is a problem inside it. Also check there is no short between the thermistor and the heater block.

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Hi Chris, thanks for the advice. I removed the thermistor and hotend wires from the mini-pcb to test them and they are reading correctly. When I re-installed them, everything seems back to normal again. I will run it as-is for a while and see if it happens again, then I'll have a look at the hotend wires as you suggested. Maybe it was a strand i'd missed when tinning the wires or something!

Thanks Nophead and Richgain