Dustin Diamond -- Saved by the Cell ... Back in Jail for Probation Violation (MUG SHOT)

Dustin Diamond is back behind bars ... not even 2 months after he got sprung early for his concealed weapon conviction.

Cops in Saukville, Wisconsin busted the "Saved by the Bell" star for a probation violation on Wednesday, and he remains behind bars Thursday morning.

Law enforcement sources tell us Screech's violation screw up is drug related.

He scored an early release on April 11 due to his handiwork with a mop and bucket during his 3 months in jail for stabbing a man in a December 2014 bar fight.