Yes, SYNCHROSCOPE is a Scrabble word!

Letter values in Scrabble US: S 1, Y 4, N 1, C 3, H 4, R 1, O 1, S 1, C 3, O 1, P 3, E 1.

Is it a valid word?

SYNCHROSCOPE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

an instrument that indicates whether two periodic motions are synchronous (especially an instrument that enables a pilot to synchronize the propellers of a plane that has two or more engines)

Not playable in Scrabble US: SYNCHRONOSCOPE, SYNCHRONISER.