While using my 858D hot air rework station, I noticed the temperature display had changed from °C to °F unexpectedly. I tried following general instructions online, but the guidance I found (including a Reddit thread) didn’t match how my unit behaved.

What I discovered

On my particular 858D PCB, the °C/°F behavior is not just controlled by buttons. Instead, there’s a hardware switch option:

  • The main PCB includes an unpopulated switch footprint labeled S3
  • Populating/enabling S3 switches the unit between °C and °F

What I did

  1. Opened the unit and located the S3 footprint on the main PCB.
  2. Installed a small switch. I considered drilling a hole to fit the switch permanently, but I decided to just let it hanging inside the case (with proper insulation of course)
  3. Powered the station back on.
  4. Confirmed the display returned to the expected °C behavior.

858D PCB

Sources