Toaster Oven Repair
2026-04-08
Our toaster oven/air fryer recently stopped working mid-toasting. I don’t remember what was being cooked at the time, but it was ok to finish to the microwave without being soggy. When it happened a second time I noticed it power cycling after it shut off.
What a great opportunity to take it apart! On the back are a mix of security T10 torx and #2 philips screws. Only the ones on the top cover needed to come off. Along the sides are 4 tabs holding the top to the bottom, the second tab on each side has a small catch. Using a shim to bend the tab out a little helped the top cover slide back and off.
Before disassembly, the toaster had stayed on normally, so I suspected that something might failing when it got hot. The incoming line connection from the plug goes to something in-line attached to the side of the oven wall that looks suspiciously like it would be a PTC or thermal fuse.
Some disassembly of the front panel is pretty straightforward, and surprisingly well heat protected with a metal plate and some fiberglass insulation. The chip on there seems to be just a “dumb” LED and button matrix controller with a serial connection to a controller that must be on the back of the power PCB. It seems unlikely that there’s an issue at the front panel, it still gets data to properly update the display and buttons even while it is power cycling.
This was a good opportunity to use all of my fun oscilloscope accessories. I put a differential probe on the line, across the thermal fuse, and a current probe on the common terminal of the heating elements. Each coil is labeled 583W, so just one bank (top or bottom) could draw nearly the full rated current. I occasionally saw a 1/2 cycle glitch in the oscilloscope current, so the toaster probably alternates between the top and bottom elements when it wants to heat both sides. There’s only one temperature sensor in the top of the oven, so it must be pre-programmed on how to split the time between top and bottom. I didn’t bother to check. The GND and 3.3V to the front panel were floating at close to line voltage. I assume it’s safe to ground them but didn’t want to figure that out while the oscilloscope was already hooked up, so I used 2 more channels to monitor the power that presumably runs the microcontroller in the oven as well as the front panel. I ran a few bake cycles, air fry, and toast, but never saw any increase in voltage across the thermal fuse or a drop from the 3.3V.
I did another check on the serial communication with the front panel. I was still using the difference between 2 channels and there’s no triggering or serial decode on a “math” signal, but it looked ok at a glance.
I left the top off and the toaster unplugged so that it could be used while waiting for further diagnosis. Plugging it in later, it was power cycling while cold! I noticed that holding any of the buttons on the front panel would stop the power cycling, so maybe the issue is with the front panel after all! Following the traces from the buttons, all six seem to use a common line to the chip. The resistances of each button were in the 210-250M Ohm range, except for the power button, that measured about 16k when open.
There’s also a diode on each button. They all measured about 0.6V forward or 700k Ohm in the resistance mode, and 160-200M Ohm in reverse. In messing around testing all of the buttons, the power button would sometimes behave like the other buttons and sometimes be very leaky. I flexed the board some and didn’t see the change, so the intermittent nature led me to suspect the button itself rather than the diode.
I removed the button, and only had a bag of narrower buttons, so mounted the new one diagonally to keep the button itself under the plunger on the front panel. I added a little more conformal coat just for good measure.
With that, everything seems to be in working order and I reassembled the whole thing!