TROUBLESHOOTING AND REPAIR
FREQUENCY SYNTHESIS
SUB-SYNTHESIZER ADJUSTMENTS 6C-5.
The following procedures cover the five adjustments on the A4 Sub-Synthesizer PCA
listed below:
R5, DAC Full Scale Adjustment
R99, Clamp Adjustment
R98, Clamp Adjustment
R106, Mixer LO Drive Adjustment
L56, 10 kHz Notch Adjustment
Note that 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.
Steering DAC Full Scale Adjustment 6C-6.
TEST EQUIPMENT:
•
DVM
REMARKS:
Steering DAC Full Scale adjustment is normally required only when U5, U6, or
associated components have been replaced, or when the adjustment has shifted.
PROCEDURE:
The Steering DAC voltage is adjusted to 10.23V with the Coarse Loop Steering DAC
set to full scale.
1. Program the UUT to SPCL 909.
2. Program the UUT to SPCL 943. This Special Function programs all DACs to full
scale.
3. Connect the DVM to measure voltage between TP6 and ground.
4. Adjust R5 for 10.23V ± 0.01V.
5. Program the UUT to SPCL 00. This clears all Special Functions.
Lower Clamp Adjustment, R99 6C-7.
TEST EQUIPMENT:
• Frequency counter
REMARKS:
The Lower Clamp Adjustment (R99) is normally required only when U35, U36 or
associated components have been replaced, when the Sub-Synthesizer VCO (A3) has
been repaired or replaced, or when the adjustment has shifted.
6C-13
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