Vintage Synth Repair

HELLO OXYGEN
I OWN AN M500 AND ALWAYS WAS IN DETUNE STATE.....AT FIRST WAS STABLE 
BUT PASSED ONE HOUR THE TUNE WAS IN OFF....SOMETIME WAS OK BUT IN 
THE MIDDLE OF THE TUNE WAS DOWN......FINALLY I DONT USE IT....ONLY 
HIS NOISES.
I DONT KNOW HOW TO TUNE IT.
LET ME KNOW HOW ARE YOUR M500

CESAR GUZMAN
CEMURECORDS