Aoyue 2702+ temperature reading very high

[amateur_24]

Hi
I have an issue with my solder iron is giving bogus temp readings. So I have it set 350 but it'll read over 400 degrees. Then a second latter it'll read over 500 degrees.

The iron only goes up to 480! AFAIK the temperature sensor and heating element is built into the iron tips.

The tip does get hot just not hot enough. I reckon the microcontroller is shutting the heat off before the tip gets to 350 because of the bogus readings.

I did try a different tip but still the same issue.

I know there's software compensation but it doesn't go that far and the temp is unstable anyway. The software is ran on a atmega 16. I reckon it's using the internal adc on atmega because I can't see any adc chip on the other pcb. There's only 3 ics. One is the atmega and the other two are Darlington drivers for the 7 segment displays at the front.

Please help I spent too much money on this soldering station. When you consider I don't use it much, I would expect it to have lasted longer.

 

[danadak]

Inspect the PCB for the controller for poor soldering, use a magnifying glass or inspection
microscope.

I would take apart the iron itself to make sure thermistor, or heat sensing component, still
attached well and in good thermal contact with heating element/tip.

Check wiring from controller to iron, use ohmmeter and move wiring to see if any intermittent
mechanical relalted issue affect wiring conductivity.


Regards, Dan.

 

[amateur_24]

Inspect the PCB for the controller for poor soldering, use a magnifying glass or inspection
microscope.

I would take apart the iron itself to make sure thermistor, or heat sensing component, still
attached well and in good thermal contact with heating element/tip.

Check wiring from controller to iron, use ohmmeter and move wiring to see if any intermittent
mechanical related issue affect wiring conductivity.


Regards, Dan.

Not easily done since the wiring is moulded into the iron itself. As for the thermistor it's integrated into the tip. I have already swapped tips but I still get the same issue

There are only 4 wires going to the connector for the iron. Two of them are for power and one of the other two is connected to gnd. So am assuming that's for the thermistor.

 

[Nigel Goodwin]

I would suggest that the problem is most likely not in the electronics, but in the temperature sensor or the wiring to it.

Presumably it feeds to an opamp in the controller (to give a decent voltage level for the processor), so if you check round the opamp and see which are outputs, and monitor the voltage on them and see how they change as the iron warms up. If you're losing the feedback (such as through an intermittent break in the cable), then the temperature will run out of control.

 

[amateur_24]

I know that the wire leading to the iron keeps coming out of the connector because there's no cable clamp and the wire is too small for that type of connector. I did find one of the wires had come off the connector.

I measured across the the other two wires and it was open circuit. I swapped tips just to be sure I didn't have a dead tip but it was still open circuit.

I think the connection between the tip and the iron has failed. Before the iron had temperature sensing issues, I had issues with it not sensing the tip is plugged in. I would unplug it then plug it in again. Then it would heat up.

Anyway am I correct in saying I shouldn't be reading open circuit?

 

[danadak]

Short answer, you are correct. T sensor circuit should read in the K area.



Regards, Dana.