![img2](images/pax/img2.jpg)
Here's the backside, just battery leads.
![img4](images/pax/img5.jpg)
I desoldered the heater and charging contacts from the board and removed it to inspect the heater.
![img5](images/pax/img8.jpg)
Removing the insulation reveals the oven. The oven is heated by the serpentine traces laminated in heat resistant plastic tape. The temperature sensor is a surface mounted thermistor that is grounded on one side with the other side connecting to the board. It most likely forms a voltage divider with another resistor on the board to supply a temperature-dependent voltage that the microcontroller can sample. The thermistor tested good with a multimeter.
![img6](images/pax/img11.jpg)
Here's the locking mechanism that is used to change the position of the mouthpiece.
![img7](images/pax/img6.jpg)
After verifying that the heater was working by testing it with a voltage from my power supply, I traced the heater wires to a transistor on the circuit board that drives them. I could barely make out a mark on the tiny SMD chip so I looked at it again with a microscope.
![img8](images/pax/img1.jpg)
At this point I was pretty sure that I had found the issue. You can tell this chip is burned out from that mark on it. Also that solder bead looked pretty suspicious. This chip was definitely getting hot.
![img9](images/pax/img2.jpg)
Since I already had the microscope out, heres a close up of the RGB LED used as an indicator. You can see the individual cathodes for each color.
![img10](images/pax/img13.jpg)
I ordered two new transistors to be safe. If you want one, you can buy this part
here
.
![img12](images/pax/img14.jpg)
Old chip removed
![img13](images/pax/img15.jpg)
Solder paste and new chip
![img14](images/pax/img16.jpg)
New chip soldered in place
![img15](images/pax/img17.jpg)
Cleaned up all the flux
![img16](images/pax/img18.jpg)
All put back together. It heats up!
![img16](images/pax/img21.jpg)
It charges! I was unsure if it would be repairable when I first opened it so I was very happy to be able to fix this one.