Pa Functional Testing - Motorola ASTRO Digital Spectra Plus Service Manual

Troubleshooting Procedures: Power Amplifier Procedures
RX MODE
LOCATION
LOW
J1
41 0
42
43
44
Q0500E 13.0
Q0501C 12.3
Q0501E
Q0503E
Q0503C 13.6
Q0504B 13.6
If the command board and synthesizer are functioning properly, the PA must be defective. Details on
troubleshooting each circuit of the PA follow.

4.5.1.1.2 PA Functional Testing

NOTE: When setting or measuring RF power at VHF follow these guidelines to avoid measurement
errors due to cable losses or non-50-ohm connector VSWR:
- All coaxial cables should be low loss and as short as possible.
- Attenuators and 50-ohm loads should have at least 25 dB return loss.
- Mini UHF to 'N' adapter, P/N 58803671321, should be used at the antenna connector. All
other connectors should be 'N' type. No other adapters, barrel connectors, etc. should be
used.
Maximum input level to the PA is 20 mW. Too much input power could result in damage to the
LLA stage.
Methods of analyzing individual stages of the power amplifiers are detailed below. Most of the stages
are Class-C and must be analyzed under relatively high RF power levels. The following information
should help in isolation and repair of the majority of transmitter failures.
6881076C25-D
Table 4-8. Power Control DC Voltage Chart (Continued)
TX MODE
TYP HI LOW TYP
0 0 0
0 2.2
1.3 7.0
2.1 3.2
13.0
12.3
0.2 0.2
0 1.5
9.0
12.9
HI
0 0 Ground
9.6 Control AMP Output (Approx 1/2-V Control)
Loop Integrator Capacitor
Control AMP Reference
A+ - CR0500 Drop
VQ0500E - B/E Drop
V pin 23 - B/E Drop
V pin 42 - B/E Drop (TX)
A+ - B/E Drop (TX)
COMMENTS
October 28, 2002
4-25