I have this PCB which is the motherboard of my pellet stove. It is reading a value "T Board" which is the temperature of the board. Now it's reading faulty values (86°C at ambient temperature) and the stove won't work normally.
I disassembled the motherboard, disconnected everything, put it on power and I can still see the temperature on the remote control and make it change using a hair dryer to heat the board. It will not change much however, up to 91°C, may be because of the faulty sensor.
The problem is, I failed to find which component is the sensor. After some research on the subject, I think it might be a thermistor but the one I found at the bottom of the board (blue near the transformer) seems to be just for the power part (it wont change the reading if I heat only this component.)
If it is an SMD thermistor, is there any tips to distinguish it from resistors/capacitors?
Full board picture:
Zoom on the part that seems the most sensitive to the hair dryer:
Following suggestions in comments, here are the things checked:
- RTC component is MCP79411, it does not have a temperature sensor according to datasheet.
- 8 pin component near ATmega is labeled 33064, an undervoltage circuit according to what I found on the internet.
- TO92 component on the top is labeled 7333-A, it's a LDO regulator. Second TO92 (between transformer and radiator) is not visible, but it goes to a connector labeled "Vacuometro" so I guess it's not a temp sensor.
- I traced ADC pins of the ATmega (ports F) but I couldn't find anything useful. Of course I could have missed something.
- I also tried moving around the hot tip of my soldering iron, but I failed to trigger any temperature change on the remote control. Very disappointing since hair dryer will still trigger a 5°C variation.