The speed at which any VCR plays is set by the speed at which the cassette was recorded. I suspect that the cassette you tried was recorded at EP if it was only half read (or SLP if it was one third read). The VCR switches itself to suit the tape.
My problem is that I have somehow set mine to, I think, PAL instead of NTSC and haven't found the way to set it back. Somewhere I don't quite understand the instructions.
Grant
January 2005