Encoder help

Can anyone tell me if there is a simple way to check (ohm) an encoder signal? I don't have access to a scope. My encoder (no info avail as it is an add on to a OEM supplied stepper) seems to count ok in one direction, but is very erratic in the other direction. Only 4 wires: (2) pwr (12V) and A & B.
Any help would be appreciated.
Thanks

Expect output of 0-5 volts, digital. 2-3 volts average when turning.
Channels should show same voltage as encoder is rotated in both directions. Suspect weak B channel. Output lower than channel A.
Borrow or rent a scope. You aren't going to pull this off without one.