I bought this one off of ebay. The problem is with the pitch knob. It worked once but never again. Played back a song I compiled and my singing sounded almost like a womans voice. I could only find normal bias cassette tapes at 90 minutes and the manual calls for 30 minute high bias tapes. That could be half the problem but do you think I need to replace the rubber band coming from the motor to the cassette mechanism and would desoldering the potentiometer for the pitch and replacing it would fix the problem and yeah, using the suggested cassette tapes?

Audio Players & Recorders - Tascam - Starter Pack for 4-Track Cassette Recorder Microphone