Fluctuating Temperature on Ormerod 1

I was printing some models and I was having issues with the temperature fluctuating wildly throughout the print. I am using Pronterface (Version 2014.03.10) and Firmware 1.09.

The start of the print would go well but eventually the temp would start to bounce back and forth by 10-20 degrees. By the end of the print, It could be dropping down to room temp or on some occasions -273 degrees. This doesn't stop the print though and it is able to finish (with some issues of under extrusion)

This only seems to be happening recently (in the last 3 or 4 prints) and it doesn't affect all prints (I printed 4 small items yesterday only 3 were affected). I am not entirely sure that the heater is broken or if it is just the temperature reporting that is at issue. I tried looking at updating the Firmware to 1.26.1 but cannot find the .bin file for this. Otherwise, I haven't changed anything else in a while.

If the fluctuations are rapid, it's a temperature reading issue. Usual causes are a bad thermistor, or a thermistor wire shorting against the hot end metalwork or something else.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

They were quite rapid. Every second or so, and it would change by massive amounts as well. One second it would be at 200 degrees and the next it could go down to 70. I assume that a temperature sensing issue could affect actual temperatures as it would be trying to correct for incorrect values?

I tried looking for shorts in the transistor but it still looks normal. There could be wear inside the heater block so I might try to pull the transistor out and take a look. I hope it isn't as difficult to remove as it was before.

Looks like it is fixed. I unplugged the thermistor and checked it out, with no noticeable issues. When I plugged it back in I noticed one connector could travel further than it did before I removed it. I think what happened was the connector got unplugged to where the only thing keeping a connection was spring in the wires. During printing, I think this would jiggle causing the connection to open slightly causing the reported temperature to decrease.

I am printing something now with no issues. Will keep monitoring it and update if it is caused by something else.