HP 85662A Troubleshooting And Repair Manual page 406

If the BW5 control line is not switching, Q3 is most likely defective. If Q3 is found to be
defective, check QS to determine if it has failed also.
Figure 1 is reproduced from the troubleshooting for the A4A5 Step Gain. It shows the
results of a quick test to determine proper operation of the 0.0 to 1.9 dB attenuator section
of the AO.0 to A15.9 dB control. As the figure shows, the steps are not exactly 0.1 dB. If the
steps are not continuously increasing (monotonic), either a control line is not switching or
a switching diode is defective. Table 6 will be useful in determining when a control line is
active.
REF
LINEAR
CENTER
Center Frequency readout will be 20.000 000 MHz for an
Note
HP 8568B/HP 85678.
The absolute step amplitudes can be determined with the MARKER A function. The
reference steps are 0.0 dB and 0.9 dB. In the Linear mode the error should be less than
The 1 dB, 1.4 dB, and 1.8 dB steps are controlled by factory selected resistors. If one of these
steps is in error by more than f 0.12 dB in the Linear mode, refer to the adjustment section
of the Performance Tests and Adjustments Manual for the procedure to determine the correct
value. The other steps should be f0.2 dB in the Linear mode.
- 9 . 9 dBm
1 0 0 . 0 0 0 M H z
RES BW 3 MHz (1)
Figure 1. 0.1 dB Step Gain Display
M K R a 1 9 . 3 6 set
VBW 3 kHz
1 . 9 0 dB
SPAN 0 Hz