Once I had a chance to check, what’s inside of such a device. Unfortunately, I haven’t taken any picture during repair process.

Device was brought to me with the words, that computer doesn’t see it and probably someone has plugged USB type B cable into device upside down.

At first I thought about burned voltage regulator or a fuse. However, when I opened the case, I could not find any burned part or any smell. I checked the power lines as much as I could and did not find any fuse, but instantly found 5 to 3.3 volt LDO regulator. The most strange thing I found was that I could not find any connection between USB connector and LDO. The power track on PCB was just going into the innermost layers after ferrite bead and I could not find any way out for it. Also I could not find anything similar to the fuse or protecting diode or transistor.

Connecting USB cable gave 5V at the beginning of power supply net up to the via. On the LDO input there was only couple of tens of millivolts. Checked for shorts and then connected power supply input via after all the filters with LDO input. And it took device alive. LEDs lighted up and blinked in sequence, Windows found new device and started installing driver for it.

I have installed some software from Dearborn website for this device and connected it once again. Checked all the functions are working, as much as I could without diagnostic cable to connect device to my car, and proper LEDs are blinking.

So I came to decision, that when somebody connected USB cable upside down and made reverse polarity power connection, the inner power track or some via did not managed to handle so much short circuit current and gave up. I have connected the power supply via to second part of the power supply line with a piece of copper wire, checked that nothing heats up, assembled the device and returned it to the owner.