Extruder heater won't turn off (and turns on automatically)

Hi,

Until recently my extruder heater was working just fine (and has been for ages)

In the last week or so, I made a new extruder heater using a different thermister (which I have, what I believe, the correct lookup table for). I changed Temparature.h (and Configuration.h for other reasons) to add the new lookup tables.

However, now my GEN6 electronics seems to be acting oddly. The heating resister in my extruder block heats up immediately I power up my Mendel. I don't even need to start RepSnapper (If I do, nothing I do in RepSnapper makes any difference - e.g. turn heater on/off, change target temp). The temperature just goes up and up (I pulled the power at 300 deg C last time).

I've tried recompiling the firmware and reloading
I've tried going back to the very original firmware (with all the old lookup table, etc, etc) recompiling & reloading.

What was particularly strange, is that last night I changed a lookup table (and NUMTEMPS and removed the 'bedtemptable' thermister table in Temparature.h) and everything was perfect. I was controlling the temperature up and down to precisely what I wanted for several hours. Then I needed to hold the heater block (disassembly/reassembly of extruder) so turned everything off. When I reapplied the power the old problem returned - the heater just came on.

Any advice?
Have I fried my GEN6 hardware?

Thanks

Pete

When this was happening to me before, it was because I'd fried the MOSFET controlling the heater. This was with a Techzone GEN3, which is a set particularly prone to that. Still, if you shorted something accidentally I'm sure you could do the same to a GEN6. Look for a chip wired closely to the terminals for the heater, and see if there's anything that looks burned.

Hi,

Thanks for the suggestion. I solved the problem (though I'm not exactly sure of the real cause)

I went back to the original firmware and applied all the changes I'd made again (I did file comparison to check I caught everything)

Now it works fine (notwithstanding some thermister/heating resister temperamental wiring that also obscured the problem). I think it must have been:
1) removalof a stray "*/" comment that I left behind after an edit in temparature.h
2) reintroduction of the 'bedtemptable' thermister table even though I don't use it (and replaced "NUMTEMPS" with "20" for that table only)
3) something else I fixed without knowing I screwed it up previously while editting the files

So, at least I didn't fry the GEN6 electronics - phew!

I still find it frightning it could have such a (dangerous?) affect - unrestrained heating just by applying the power. A lesson there for me, I think.

Cheers

Pete

Edited 2 time(s). Last edit at 10/03/2011 06:33AM by Flackster.