I've an A8 that has an apparently dead transport control system - capstan spins when tension arms are up, all power supplies, motors & solenoids test good. Transport keys have NIL effect.
You can not try and fix a machine by osmosis. You need to get into the deck with the schematics and service manual like I do all the time. Sometimes there are defective filter caps on the Vcc and other times a reset part is stuck and will not allow the processor to reset into operation mode or it could be as easy as a safety tension arm switch or even that a dummy plug is missing it it uses one. Processors that a lot of DIY people look for usually do not go out until they are making sparks then they might be out due to the sparks. I am not sure I have ever come across an A8 but I work on stuff like it all the time. Start by checking all voltages out of power supply which takes a DVM.
