Part 4 Of 5 - Motorola ASTRO XTL 1500 Detailed Service Manual

5-58
5.6.47 RF Power Amplifier (RFPA)—No or Low TX Power Output (700–800 MHz)—

Part 4 of 5

Specific Notes:
1. Remove C6501 and solder the center conductor of a small 50-ohm, coaxial cable to
VN_B6500. Solder ground to the gold shield track adjacent to VN_B6500. Attach an RF
milliwatt meter, key the transmitter, and measure TX_INJ power. Then, remove the coaxial
cable and replace C6501. Remove the solder added to shield track.
2. Remove R0977 in the power control section, and measure the resistance between VCNTRL
(VN_B6503) and ground. Replace R0977.
3. If U6500, VD1, is incorrect, inspect the bias feed circuitry (L6501 and C6504) and interstage
match components (L6502, C6506, and C6503). If U6500, RFOUT, is incorrect, inspect the
bias feed circuitry (L6500 and C6500).
4. Remove L6501 and measure the resistance between VD1 (VN_B6501) and ground. Replace
L6501. Remove L6500 and measure the resistance between RFOUT (VN_B6504) and
ground. Replace L6500.
5. Inspect C6502, C6509-11, and R6521-5.
6. If the Q6520 gate bias is incorrect, inspect the bias feed circuitry (R6520 and C6520). If the
bias feed circuitry is functional, then go to the Power Control—No or low VGBIAS flowchart. If
the Q6520 drain bias is incorrect, inspect the bias feed circuitry (L6521, C6521-2, R6526-7,
and L6521-5).
7. Remove R6520 and measure the resistance between Q6520 gate and ground. Replace
R6520.
8. Remove L6521 and measure the resistance between Q6520 drain and ground. Replace
L6521.
9. Inspect C6541-2, C6544-5, C6547-8, C6565-6, R6550-7, and R6559.
10. If the Q6540 gate bias is incorrect, inspect the bias feed circuitry (R6540 and C6540). If the
gate bias feed circuitry is functional, then go to the Power Control—No or low VGBIAS
flowchart. If the Q6541gate bias is incorrect, inspect the bias feed circuitry (R6543 and
C6558). If the bias feed circuitry is functional, then go to the Power Control—No or low
VGBIAS flowchart. If the Q6540-1 common drain bias is incorrect, inspect the bias feed
circuitry (L6542-3, C6559-60, R6544-5, and L6521-5).
11. Remove R6540 and measure the resistance between Q6540 gate and ground. Replace
R6540. Remove R6543 and measure the resistance between Q6541 gate and ground.
Replace R6541.
12. Remove L6542 and measure the resistance between Q6540-1 drain and ground. Replace
L6542.
13. Inspect R6560 and C6549-57.
14. If the antenna switch bias voltages are incorrect, inspect R6547-8, L6700, and L6702-3, as
well as perform diode checks on D6701-2.
15. Inspect the remaining antenna switch parts (C6700-5).
16. Inspect L6720-2 and C6720-1.
17. Inspect D6730, R6730-2, R6735-6, L6730, and C6730-1.
June 15, 2005
Troubleshooting Charts: Flowcharts
6815854H01-A