Pioneer DEH-840MP & DEH-850MP Both Appear Dead

I have one each of these models in the shop with the exact same symptom.
Both appear to be dead. In both cases if you hand wind the power face so
it is open and then power the unit with 12 volts to the yellow and red
wires, the face will close automatically. That is the only "sign of life".
Neither of these units will respond to any buttons nor do you see the
displays light up. Any help would be appreciated. Thanks, Mike

 

You're going to need a schematic for sure!

 

There is a service Bull on this. you will need to order the flex cable
mod for the front panel.