That sounds like a frustrating problem, I haven't looked at the sensor circuit in detail, my best guess is it is a simple IR RX/TX pair. The RX is prob a simple IR transistor that activates with any IR light which turns on a digital out, being 5v. You can see which one is the TX by observing a small red light through your cellphone camera. If there is 5v when it is not connected to the GEM2, and this drops to 0V when connected, then the fault could be the GEM2, a shorted track, or a faulty RX transistor. I would connect it to a bench top power supply and observe the current draw when the sensor is connected and disconnected. This would guide me to my next move, if there is a large current draw then this would indicate a short, I would crank the voltage up to maybe around 300-600mA for a short period and try and locate what area is getting warm.
once you are happy the sensor is alternating between 0v and 5v with a reflector, it still won't show cadence in the app unless the sensor is alternating extremely fast, i.e. you prob need to assemble it back together and spin the flywheel, it is very hard to register by hand only
Last edited by rogers2000; 04-09-23 at 11:50 PM.
Reason: further info