Bed & Nozzle temperature issue Ender 3V2

[MrSpan]

After an aborted BLtouch upgrade I decided to return to a tried and trusted FW. I had saved it for such an event and uploaded to the Ender 3V2.I enabled pre-heat and went about manual levelling. Unfortunately I hadnt noticed that the max PLA temp for the nozzle was set to 807C and the bed was a few hundred C (maybe 400C -ish). No idea how, assume corruption during upload. I only noticed after a few minutes, turned all off and left to cool.When I turned back on again I uploaded a different FW and then went back to my trusty one again, and this time PLA settings were correct.But now when both nozzle and the bed start to heat, all is well initially, but when they get within @10C of the desired temp they seem to give up and settle for a temperature @10C below the set-point. I took the bed off and checked the themocouple/thermistor hadnt come adrift with the excess bed heat, but it was fine. With a bed set Temp of 50C, from turn on, I measure the 24V DC at the element and all is well until @40C and the 24V shuts off, as if its reached temp, and it then pulses the 24V and keeps the temperature @40C.If I then manually set to 60C it once again enables the 24V and until it gets to @50C and then keeps is at 50C.I cannot think what would do this? damaged to the main board somehow? or somehow the PID settings are wrong for the temperature feedback loop.After few minutes of this the printer alarms that the "nozzle temperature too low" and requires a power cycle.I did have an overtemperature issue a couple months ago, but that was assumed to be overheating on the mainboard and increasing the cooling fan on that seemed to fix that and I have had no other issues until today.

[MrSpan]

Ok I think I have found the cause and its an odd one, so I thought I would post it in case anyone else comes up against this in the future. I opened the motherboard cover to check if any connections were loose or for any obvious visual issues. The only slightly odd thing was that one of the wires from the bed thermistor was kind of bent round under the board and just happened to be running alongside one of the wires from a buck converter I fitted in the mainboard bay to drop the voltage to a 5V quiet fan. Bucks by there nature are noisy and so I just moved the wires to be apart from each other. When i tried next, all works great. I assume EM noise pickup was triggering the temp control loops.

[curious aardvark]

yeah pinch the thermistor wires and they'll give odd readings.
Or anything that modifies the current in the wire :-)

Glad you got it sorted.