Fritz Box 7360

How to fix a dead Fritz Box 7360

I recently received a fritz-box 7360 which seemed to be dead. No LEDs were blinking, and the box didn’t connect to anything. So a Hardware defect was pretty obvious.

I carefully opened the Box. Pay attention to the hidden screws!

I hooked up the box to a powerful bench supply and suddenly one of the Reverse-Voltage-Diodes instantly released its magic smoke. So now it was clear that there is a short circuit causing the Problem… :zipper_mouth_face: I should rather have checked the Input with a Multimeter first, instead of hocking up a big Power-Supply, but I initially anticipated that maybe the external Power supply was the Problem.

I should really invest in a proper Lab-Bench-Power supply.. 😳.

After identifying that the Problem might be a shorted Capacitor, I exchanged the Reverse-Voltage-Protection-Diodes and soldered two cables to the inputs to easily power the board.

Together with my Flatmate Andre, we set Our Power-Supply to about 0.3A at 12V and started to look for the Problem.

Unfortunately we don’t own an expensive Flir, so we relied completely on our Fingertips for identifying the shorted capacitor.

After searching for about 10 minutes we identified the Area where the ~3W of Power seem to generate Heat. Following a Hint on microcontroller.net we used some Cooling-Spray to freeze the area and waited until a thin layer of ice has emerged on the PCB-Area, where we expected the damaged component 🎉.

Running Power through the ’’frozen’’ PCB instantly melts the ice on the component, which is damaged. That way we sorted out which capacitor was the Problem. We removed it and checked the Resistance – 0Ohm 🥶.

Unfortunately there are no schematics available online to find out what SMD capacitor should be installed at that spot. But as there were two optically identical capacitors installed in parallel, we assume the capacitor originally had 10uF like the other one. We didn’t replace the cap and hoped the other one will be enough .. and we were right the Fritz-Box booted up perfectly fine and runs as good as before. In case you have a 10uF 0805 Capacitor on hand replace it - there is probably a reason for it to be there 😇.

After all a very easy fix – replace two Diodes and remove one Capacitor and 500g of resources are saved For our Planet 😎.