Hello guys, I really need your help 
What i have:
GH Motor 7.2vdc 50:1 175rpm (6mm shaft) (GHM-04)
Quadrature Motor Encoder (QME-01)
When I attach the encoder to motor, the encoder works, and the output are two squre waves, however the peak to peak values are 5V and 1.2V…
And, when I turn to measure the output seperately, there is no output at all… I use 5V voltage to power the encoder.
What happened? I want to cry…
What are you using to measure the pulses? I’m having trouble understanding the problem description.
oscilloscope 
Well we’re going to need more information. Can you please take another stab at defining the problem? Can you post images of the wiring? Is the problem showing with the encoder removed from the microcontroller, just power and ground connected…
Sorry for my poor description.
I just follow the instruction on this page:
www dot lynxmotion dot com/images/html/build095 htm
and i use a DC power supply for 5V input.
I use osciloscope to see the outputs from the yellow wire and green wire.
They both have square wave, one’s peak to peak value is 5V and the other is 1.2 V.
After a while, the output disappeared…
other than the oscilloscope what else is attached to the encoder outputs?
nothing else
It appears the encoder is either defective or has been damaged. I’m sending you a PM.