Here are few steps to check if the test diode is working:
a. make sure that the diode is ok (bonds can break sometimes) - so apply (do it manually) small bias in reverse and forward direction and see if the current changes as expected.
b. make sure the amplifier bias is on - use 13 V or use the voltage output (LEMO) from the laser power supply. There should be considerable change in noise for on/off.
c. make sure that the bias gets to the sample - measure it with voltmeter at the connector going to the sample
d. apply 20 V to the diode (positive voltage at the pin), set the laser to 20% DAC value. Point the laser directly to the diode (not through the Beam expander) from a small distance and move it across the diode surface. You should see the signal immediately after trigger pulse