hifi engine

Marantz 5025 plays too slow

Hi everyone, I need a little help here. I have a Marantz 5025 cassette deck that refuses to play a the proper speed, it's way too slow. I've installed new belts, cleaned all idlers and even replaced the motor. I can't find much data on this deck or even the 5010, the model below. I did measure the voltage at the motor and it read 1.132 volts. The original motor has 8v stamped on the back of it, so i would assume somewhere between 6-10 volts should be read at the motor. Something appears to be limiting the voltage to the motor. Any ideas ?
Thanks, Vern