TROUBLESHOOTING AND REPAIR
RF LEVEL/AM
Mod Control PCA Detector Offset Adjustment, R28 6D-13.
The detector offset adjustment sets the detector offset voltage. The adjustment also
affects AM Depth Adjustment, R10. Repeat Section 6D-14 after this adjustment.
TEST EQUIPMENT:
• Power meter
• Power sensor (High-Level)
REMARKS:
The UUT must be operated at room temperature for at least one hour with the module
plate cover in place before continuing with this adjustment procedure.
This adjustment is normally required only when components in the detector or
detector linearizer circuits have been replaced. If the detector offset is adjusted,
perform the AM depth adjustment.
CAUTION
The detector offset adjustment directly affects the output level and should
not be made indiscriminately.
PROCEDURE:
The detector offset adjustment, R28, is adjusted to provide a 24-dB change in output
power for a 24-dB change in the level DAC. This is done while operating in fixed range.
1. Access R28 by removing the instrument bottom cover.
2. Program the UUT to SPCL 01, 350 MHz and +12 dBm.
3. Program the UUT to SPCL 51. This Special Function enables amplitude fixed
range.
4. Remove the detector offset adjustment access screw from the bottom module plate
cover.
5. Zero the power meter.
6. Connect the power sensor to the UUT RF OUTPUT connector.
7. Note the power meter reading.
8. Program the UUT for -12 dBm using the EDIT knob. Be certain to use the EDIT
knob to change the amplitude for this step or the special function will be
automatically cleared.
9. Adjust the detector offset adjustment, R28, for a power meter reading 23 dB ±0.1
dB below the reading obtained in step 7. Program the UUT to +12 dBm.
10. Repeat steps 7 through 9 until the difference between the power measurements is
23 ±0.1 dB. This adjustment should require three or fewer iterations.
6D-12
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