4-11
Verification and Service Information
Service Information
3
If the voltage reading is not +5.7 V dc, adjust the +5V ADJ potentiometer (R12)
for a reading of +5.7 V dc ±50 mV.
Troubleshooting
The main functional blocks of the Agilent 11982A are the power supply, the
photodetector and the electrical amplifier unit.
Figure 4-1. Agilent 11982A Block Diagram
The
Photodetector and
the Electrical
Amplifier Unit
Modulated light enters the photodetector through a single mode fiber front-
panel connector. Light is collimated, then focused onto a PIN photodetector.
Photons are absorbed in the photodetector. Electron-hole pairs are generated
by the light, which produces the photocurrent. The photocurrent is amplified
by the dc to 22 GHz preamplifier. If the photodetector and electrical amplifier
unit fails, the Agilent 11982A must be returned to Agilent Technologies for
service.
Troubleshooting
the Power Supply
If the +5 V power supply output voltage is low, the power supply could be in a
current-limiting or overvoltage crowbar mode. If the power supply is too low,
use the R12 potentiometer to decrease the voltage, then cycle the power of
the Agilent 11982A. Decreasing the voltage and cycling the power may bring
the power supply back to normal operation. If the power supply output voltage
cannot be brought within tolerance, disconnect the power supply from the
photodetector and electrical amplifier unit, and recheck the +5 V power sup-
ply. If the power supply is still low, replace the power supply. If the power sup-
