Vintage Synth Repair

I have a Yamaha PF-15 Professional Electronic Piano that
needs the keys cleaned.

I have a copy of the owners manual but need to know how to
open and clean under the keys, etc. The owners manual don't
have this info. I see hinges on the back to somehow tilt
up the top but I don't see what screws need to be removed
to open and what exactly lifts up.

Can someone explain how to open one up or know of a free PDF
repair manual for this model. The PF-10 Electronic Piano may
be the same.

Fitting instructions for a PF-15 KENTON MIDI Kit with step
by step fitting guide plus diagrams of where to connect what
would also help me.

Also what was the list price on this Electronic Piano when it
was new? The PF-15 was Yamaha's flagship FM-synthesis
electronic piano when new.