Philips 'UFO' 303 intermittent problem
 

I've one of these 'UFO' record players with an intermittent amp problem. Most of the time it works fine, occasionally, when turning it on there's no output apart from a slight hum/static. A sharp tap on the metal mounting frame/heatsink will usually bring it back to life.

Typically it's fine at the moment and has been for the last few days...

Ideas on where to look for the cause appreciated!

Schematic from inside the player attached.