Ninja DCT401 Double oven/air fryer Possible microprocessor issue?

[tbsmith]

I'm having a random issue with this otherwise nice double oven/air fryer. It sometimes does not respond to the controls. Sometimes only the upper control buttons work, sometimes they all work and sometimes none of them work. The power supply is good as the control board has a steady 5V and 3.3V. The pushbutton switches are all good as tested with multimeter. When the buttons are working, there is about 2.5V to the high side of the pushbutton. I'm assuming pressing a button grounds the input pin to the microprocessor. When the buttons are not working, there is about 0.3 volts on the high side. Since some buttons work (with the 2.5V) at the same time as the others that don't indicates to me that the power supply is okay. Leaving it unplugged overnight sometimes helps, but not always. All solder joints seem to be good under magnification. I'm thinking there might be a bug in the firmware or a problem with the microprocessor due to the random nature. Does that sound like a possibility? I purchased an FTDI USB adapter hoping that I can check the firmware, but having never used one before. Is that something one can learn fairly easy, or is there a steep learning curve? The micro is an STM 32 ARM Cortex.

I couldn't find any youtube videos on repairing this model and no luck finding a schematic either.

[CapLeaker]

I am betting that the firmware on the STM32 is locked. Only thing you can do is to swap in a new board. I haven’t gotten a device with an STM32 that wasn’t locked. Look around on Ali… maybe you find a board for cheap.

[tbsmith]

I didn't find any control boards on Ali, but saved a search on eBay, something may come up. Thanks so much for sharing your experience with STM32's; that saved me a bunch of time trying to learn how to program or even access it! Worst case is that I will strip it for parts.

[CapLeaker]

Maybe call the manufacturer Ninja and ask them for a replacement board?

[lotas]

First, check the processor power supply for pulsation (or replace the electrolytic capacitors in the power supply), regarding the buttons, membrane buttons can "leak", that is, have a leak between the membrane and the contact pad and create internal resistance and a false triggering occurs, while no button will work (this does not look like a firmware failure).