Fluke 6080A - COARSE LOOP PCA ADJUSTMENTS 6 C-17.; Discriminator Video Amplifier Offset Adjustment, R102 6 C-18.

TROUBLESHOOTING AND REPAIR
FREQUENCY SYNTHESIS
These levels are as measured on the spectrum analyzer. The actual levels are 20 dB
higher. The levels in Table 6C-5 are approximate and can vary as much as ± 3 dB.
Table 6C-5. Discriminator RF Section Levels
FRONT PANEL
FREQUENCY
544 MHz
704 MHz
1048 MHz
COARSE LOOP
FREQUENCY
640 MHz
800 MHz
960 MHz
Q404-C
-9 dBm
-11 dBm
-9 dBm
Q405-C
+3 dBm
-3 dBm
-2 dBm
C421
+3 dBm
0 dBm
-2 dBm
A25-J9
+3 dBm
-6 dBm
-5 dBm
If the power is correct at the collector of Q405, but low at C421, the problem is
probably in the switched low-pass filter. If the power is correct at C421, but low at the
cable connecting to J10, the problem is probably in the coupler or delay line. If the
power is correct at the output of the delay line and the DC voltage at the output of the
mixer is nearly zero, the problem is probably a defective mixer. Any problem with the
delay line assembly will necessitate replacing the whole assembly, including the cable.
To check the discriminator amplifier (Q101-105), remove the end of the resistor that
connects to the Discriminator PCA (A25-J3). Connect the resistor to the UUT front
panel MOD OUTPUT. Program the UUT to MOD FREQ 1 kHz and MOD LEVEL 4
mV. There should be a 500-mV p-p 1 kHz signal at TP9.
COARSE LOOP PCA ADJUSTMENTS 6C-17.
Refer to Table 6C-6 for information about the test points for the A2 Coarse Loop
PCA. The following procedures cover the five adjustments on the A2 Coarse Loop
PCA:
R102 Discriminator Video Amplifier Offset
R221 Steering Gain
R227 Acquisition Oscillator Level
L601 40-MHz Oscillator Tuning
L612,3 80-MHz Filter Tuning
R617 80-MHz Level
L205 2-MHz Notch Adjust
SW502 Alternate Reference Frequency Selection
These adjustments are not routine and are required only when associated components
have been replaced or when the adjustment has been changed or has shifted.
Discriminator Video Amplifier Offset Adjustment, R102 6C-18.
TEST EQUIPMENT:
• DVM
REMARKS:
Discriminator Video Amplifier Offset adjustment is normally required only when
Q102 or any associated components have been replaced or when the adjustment has
shifted.
6C-26