Emtb repair
September 2026
After riding the bike it throws an 502 error. This error indicated fault in the lights, but the bike has no lights.
Software diagnosis
Before taking the bike apart, we can try using software to recover a more detailed code. The code now is 502, but can be expanded using the Bosch dealer software. The bike has a USB connector at the computer, which can be used to charge external devices or talk to the bike. This software is normally limited to dealers. But after a bit of searching we find the needed software and a patch. After then installing on a fresh laptop for safety reasons, we can connect to the bike and read the extended code. The extended code is 0x50212c. This code indicates a voltage error in the light circuit. Resetting the error codes also does not work.
Disassembly
After confirming that the error is not software related, we can start disassembling the bike. The first step is to remove the pedals and the crank. This is done using a special tool. After that, we can remove the motor cover and the motor itself. The motor is held in place by a few large bolts.
Opening the motor
After removing the motor, we can open it. The motor is held together by a few screws. After removing these and opening the cover, we can see the inside. There is the PCB, the motor itself and a few large gears. The PCB is removed by removing a few screws and carefully lifting it up to loosen the sealant. This version is an older model, which required desoldering the motor wires to remove the PCB. Images online show the newer version uses a connector instead.
Drawing a crude schematic
After taking out the PCB it is inspected visually. No obvious damage is found. Looking at the PCB, we can see a few chips. The larger ones are microcontrollers. Two smaller chips at the edge of the PCB have inductors and capacitors next to them. This setup usually points to a switching regulator setup. Looking up the part numbers, we can confirm that these are indeed switching regulators. One regulator is used to supply the microcontrollers and computer at the handlebar, the other one only connects to the light connectors. Looking up the datasheet we can estimate how the circuit should be built up. Probing around we can confirm the board matches the datasheet.
Finding the fault
During the probing, I noticed that the output of the light regulator was directly connected to the positive battery terminal. This means that when powered on the lights will receive 36V directly instead of 12V. Since there is no obvious short on the PCB I desoldered the regulator. The short went away, and measuring the chip directly indicated that the chip was indeed faulty. The chips are TPS57160. These appear to be out of stock everywhere. TI indicates a newer chip variant is available, the TPS54160. This chip is pin compatible, has the same equations for setting the output voltage and has better tolerances. After ordering a few of these chips, I soldered one in place of the faulty one. The output capacitors and Schottky diode were also replaced. The diode out of precaution. The capacitor was replaced since its rated 25V, but since it has been exposed to 36V, it is possible that it has degraded. After soldering the new chip in place, the bike was partially assembled. After inserting the battery the computer turned on and no fault was shown. The speed was also working by turning the wheel.
Reassembly
After confirming that the fault is fixed, the bike can be reassembled. Before putting the PCB back in place, some gasket maker is applied to the housing. This ensures no water can enter trough the sides of the connectors. The crank and pedals are also put back in place. The bike is now ready to be used again.