This Technics Twin Cassette Deck had me running round in circles, looking for an electronic fault but it turned out to be an electro-mechanical one. It reminded me to give the mechanism a good look over BEFORE starting to fault find, that would have saved a lot of time. But in the end, I was able to repair the mechanism and return the unit to a very happy customer.
The initial problem with this deck was that deck 1 would not open when the eject button was pressed. My initial thoughts was that there was some problem with the electronic control of the deck and had I looked more carefully at the deck's actions when I switched it on, I would have noticed that the deck was unloading then loading again, stopping in the "play" mode but not going into play. This meant that as the deck was in a loaded mode, it could not open the door when eject was pressed.
I missed this and went on to go through the process of diagnosing the electronics until I realised the mech was stuck in play mode.