This is probably not a RAMPS issue, but since that's the controller I was using, here goes.
My hotend (a J-Head) has been very intermittent lately. My printer has been working great for almost a year, but yesterday when I turned it on and started warming it up, the
hot end wasn't heating up. I reset the arduino and re-established the connection, and everything seemeed to be OK.
Again tonight, it wouldn't heat up, and it wasn't being responsive to the same reset process, so I set about removing the RAMPS from it's enclosure. Once I got it opened up,
it started working again, so I started a print. I wasn't really paying attention to it, but a few minutes later I saw that there were several "Cold extrusion prevented"
messages on my host software. I looked at the temperature graph, and sure enough there was a dip. It had recovered, and was working normally again, but there was a 20 second
window where the temperature was low.
After this, I was watching more closely. It never got cold enough to prevent extrusion again, but there were several temperature dips. When things were working fine, I
noticed that the LED next to the MOSFET was flashing. When the temperature would start to dip, the LED would come on solid and it would remain solid even though the
temperature would continue to go down. Several times it got pretty close to the cold extrusion threshold when the temperature would start to rise and the LED would start to
flash again.
The LED behavior tells me, I think, that the thermistor is working OK. It just seems like the resistor is not putting out heat when the MOSFET is on full. It seems to me
that if the problem was the resistor, or the MOSFET, it would just fail and stop working altogether. I'm hoping it's just the wiring - a loose screw at the terminal block, or
perhaps a bad in-line connector near the extruder. Now that things are open, I'm going to very carefully make sure everything is secure, but if anyone can offer any other
advice based on my description, I'd appreciate it.
Thanks.
