Music Hall mmf-7 spins faster

I have a Music Hall mmf-7 turntable (EAR 834P phono preamp) and it spins faster than normal. I bought a new motor and a new belt from Roy Hall, but it didn't change a thing. I borrowed my friends' motor (he has an mmf-7.1): no change... I even bought a Pro-Ject Speed Box (on Roy Hall's advice): it still spins faster. My cartridge is a Sumiko Blackbird. I really don't know what much else to do: any ideas? Did someone run into this problem?

I am desperate.