Extruder temp issue

[nokianich]

Hi,

Left working printer overnight and when I woke up this morning I found out that printer head is all the way to the left, bed is lowered and my prints are not finished (mat be 30%). I have started a fresh print and when it was readu to move to the right to ooze print head didn't move and I saw a lot of error messages in the log (Fix errors and M999 fo restart). I reset Rambo, started printing again, temp of bed and extruder went up, printer head moved for ooze but didn't ooze any filament, I did stop printing and was trying to extrude filament manually but extruder motor started to click and no filament showed up, I retracted filament and then I found out that extruder is not hot, although it shows 240 but it was not, I easily touched black part with fingers. And s#d show me temp around 240. I turned off printer, restarted a computer and it was showing 220C and still why I type this message it slowly going down, 198.6, 198.5, but sometimes i goes up again : 198.6, 199.0

I reset rambo already. what else can be done? right now hot end is ice cold

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[insta]

"Fix errors" is hotend thermistor came detached and the motherboard lost signal to it. Check all the wiring in that loom for loose connections or breaks.

[nokianich]

"Fix errors" is hotend thermistor came detached and the motherboard lost signal to it. Check all the wiring in that loom for loose connections or breaks.

Checked all connection and wiring. Came back to 20° but when I turned on Hot-end heat temp jumped to 187 in couple seconds and back to 60, then again 180 and 70... Makergear sent me a new thermistor already.

I think it was bad from the beginning because I saw that every time Hot-end heats up temperature could go back couple degrees, for example it climbs and in about 220 it goes several degrees down, for example, 210.9, 211.5, 212.1, 212.1, 211.4, 210.3, 209.4, 208.6, 208.6, 209.8, 210.3 and so on.

[ednisley]

210.9, 211.5, 212.1, 212.1, 211.4, 210.3, 209.4, 208.6, 208.6, 209.8, 210.3 and so on.

Each value comes from a measurement of the voltage across the thermistor, running that number through a lookup table, and displaying the result as a temperature. Tiny variations of the thermistor voltage, due to either small temperature fluctuations or random noise, alter the input number and select a different table entry. The input voltage resolution isn't all that good, so even a "constant" temperature will seem to vary by a few degrees due to noise: you're seeing nearby table entries in quick succession.

In practical terms, a few degrees doesn't make much difference; the average is what counts.

However, large step-change "temperature variations" come from a broken wire or failed connector that changes the voltage by disconnecting the thermistor. In general, the thermistor cable inside the wire harness will fail, rather than the thermistor leads, because the cable sees all the flexing.

The fact that the reading returned to normal when you fiddled with the wiring suggests that the thermistor is fine and that there's a break in the cable; if that's so, then the new thermistor will behave the same way.