This is used to provide stable 5V to the Atmel controllers. even worse than I thoughtħ805 voltage regulator indeed. Seems that the big thing is a power regulator to obtain the 5V. I hope the link is not against any forum rule. I just need to know what the good diode/transistor reference is. I believe this is the culprit of all faulty cables and an easy soldering job.

What is the reference on the small transistor, which was replaced on the white board with the big one? Perhaps the specs are out of limit. I asume it is powered by the obd2 port and some component on the pcb is broken. The problem is with the communication to the microcontroller (atmel chip i think). This goes straight to the FTDI rs232 to usb converter.

The cable consists of a microcontroller that implements the k+dcan protocol and has a rs232 interface for pc communication.