First take the top of the unit off by taking the 4 side screws and 6 back screws off with a philips #2 then locate the transport

The transport in in the rectangle and the drum with the audio heads is circled in the back.

It is shiny silver and has 2 heads on opposite sides from each other

each heads is unbelievably delicate, so never touch them with your fingers or attempt to adjust the set screws.