Pa Functional Testing; Table 4-14. Dc Voltages And Input Power Chart - Motorola ASTRO Digital Spectra Plus Detailed Service Manual

Uhf & vhf 800 mhz mobile radios
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Troubleshooting Procedures: Power Amplifier Procedures

4.5.1.3.2 PA Functional Testing

To test the PA assembly for proper operation, perform the following steps:
1. Disassemble the PA assembly from the radio, leaving the power cable connected to the rear
connector. Replace the PA shield and cover. Disconnect the coax connectors and the ribbon
cable. Connect a power meter to the antenna port using minimum cable length.
a. When setting or measuring RF power, follow these guidelines to avoid measurement
errors due to cable losses or non-50-ohm connector VSWR:
- All cables should be very short and have Teflon dielectric.
- Attenuators and 50 ohm loads should have at least 25dB return loss.
- Mini UHF to 'N' adapter, P/N 58-803671321, should be used at the antenna connector.
All other connectors should be 'N' type. No other adapters, barrel connectors, etc. should
be used.
b. Maximum input level to the PA is 20 mW. Too much input power could result in damage to
the LLA stage.
2. Apply the input power and DC voltages indicated in
assembly. To make the DC connections, use small spring clips or make a test adapter similar
to that shown in
Test
Transmit
Receive
a. Set initially to zero. Increase value until power equals 28 watts or 9.2 V maximum.
Do NOT exceed 9.2 V.
3. Apply the required input power via an adapter cable. For this application, non 'N' type
connectors are acceptable.
4. With the applied control voltage initially at 0 V, slowly increase the voltage until power out
equals 55 Watts. Power should rise smoothly with control voltage once the turn-on threshold
is reached. Control voltage should not exceed 8.0 V.
5. If 8.0 V does not produce 55 Watts, then a failure exists in the power amplifier circuit.
6. Refer to the voltage chart (see
they are not within the limits shown on chart, then a failure exists in the PA assembly.
7. If the voltages in the chart are correct, verify that the injection is at least 10 mW (see the VCO
Troubleshooting Section).
6881076C25-E
Figure 4-6 on page
4-40.

Table 4-14. DC Voltages and Input Power Chart

CONTROL
Keyed 9.4 V
9.4
0
Table 4-15 on page
Table 4-14
to the power amplifier
POWER IN
VOLTAGE
(mW)
DRIVE
a
See note
10
0
0
4-40). Measure the indicated voltages. If
4-39
A+
(V)
13.4
13.4
September 5, 2008

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