I have assembled the circuit and the control box for the quadrant magnetic levitation yesterday. The final setup is shown

in the figure below:

Due to my carelessness, I I connected the wrong ends of the power supply. I damaged 4 op-amp and one voltage 

regulator during this assembly. This stupid mistake spent me several hours to fix, and I got a bitter lesson;-(

Afterwards, I replaced those op-amps and reconnected the power supply . Kiwamu helped me and we measured

the transfer function of this circuit.  The transfer function agrees with  the specification in the schematics which

has a integrator below 1 Hz and a differentiator from 5 to 20 Hz. The bode plot for the measured transfer function

is the following:

Today I tested the photodetector parts and found that there is a mysterious oscillation. Whenever I connect the

photodector input A of the circuit (as indicated in the figure below),

the output of the op-amp has a 500k Hz oscillation shown up in the oscilloscope.This happens even A is disconnected from

the photodetector and connected to an open end wire. I don't know how to eliminate it, and its amplitude is so large (peak to

peak is around 2.5 V) which completely dominates the photodetector output. Does anybody has some ideas? Thanks.