Motorola ASTRO Digital Spectra Service Manual page 7

Table of Contents
Chapter 4 Troubleshooting Procedures ............................................. 4-1
4.1 ASTRO Spectra Procedures.......................................................................................................... 4-1
4.1.1 Handling Precautions........................................................................................................ 4-1
4.1.2 Voltage Measurement and Signal Tracing........................................................................ 4-2
4.1.3 Power-Up Self-Check Errors ............................................................................................ 4-2
4.1.3.1 Power-Up Sequence................................................................................................ 4-3
4.1.4 RF Board Troubleshooting................................................................................................ 4-5
4.1.4.1 Display Flashes "FAIL 001" ..................................................................................... 4-5
4.1.4.1.1 Incorrect Values at U602, Pin 19 ...................................................................... 4-6
4.1.4.1.2 Incorrect Values at U602 Pin 25 (MODULUS CONTROL) ............................... 4-7
4.1.4.1.3 Incorrect Voltage at Positive Steering Line....................................................... 4-7
4.1.4.1.4 Incorrect Values at U602, pin 27 ...................................................................... 4-7
4.1.4.2 Review of Synthesizer Fundamentals ..................................................................... 4-7
4.1.4.3 Second VCO Checks............................................................................................... 4-8
4.1.4.4 Troubleshooting the Back-End ................................................................................ 4-8
4.1.5 Standard Bias Table ......................................................................................................... 4-9
4.2 ASTRO Spectra Plus Procedures................................................................................................ 4-10
4.2.1 ASTRO Spectra Plus Power-Up Self-Check Errors........................................................ 4-10
4.2.2 ASTRO Spectra Plus Power-Up Self-Check Diagnostics and Repair ............................ 4-11
4.2.3 ASTRO Spectra Plus Standard Bias Table .................................................................... 4-12
4.3 VCO Procedures.......................................................................................................................... 4-13
4.3.1 VHF Band ....................................................................................................................... 4-13
4.3.1.1 VCO Hybrid Assembly ........................................................................................... 4-13
4.3.1.2 Out-of-Lock Condition............................................................................................ 4-13
4.3.1.3 No or Low Output Power (TX or RX Injection)....................................................... 4-15
4.3.1.4 No or Low Modulation............................................................................................ 4-15
4.3.2 UHF Band ....................................................................................................................... 4-15
4.3.2.1 VCO Hybrid Assembly ........................................................................................... 4-15
4.3.2.2 Out-of-Lock Condition............................................................................................ 4-16
4.3.2.3 No or Low Output Power (TX or RX Injection)....................................................... 4-16
4.3.2.4 No or Low Modulation............................................................................................ 4-17
4.3.3 800 MHz Band ................................................................................................................ 4-18
4.3.3.1 VCO Hybrid Assembly ........................................................................................... 4-18
4.3.3.2 Out-of-Lock Condition............................................................................................ 4-18
4.3.3.3 No or Low Output Power (TX or RX Injection)....................................................... 4-19
4.3.3.4 No or Low Modulation............................................................................................ 4-19
4.4 Receiver Front-End (RXFE)......................................................................................................... 4-20
4.4.1 VHF Band ....................................................................................................................... 4-20
4.4.2 UHF Band ....................................................................................................................... 4-20
4.4.3 800 MHz Band ................................................................................................................ 4-20
4.5 Power Amplifier Procedures ........................................................................................................ 4-21
4.5.1 VHF Band ....................................................................................................................... 4-21
4.5.1.1 High-Power Amplifier ............................................................................................. 4-21
4.5.1.1.1 General Troubleshooting and Repair Notes ................................................... 4-21
4.5.1.1.2 PA Functional Testing..................................................................................... 4-25
4.5.1.1.3 Power Control and Protection Circuitry........................................................... 4-28
4.5.1.2 25/10 Watt Power Amplifier ................................................................................... 4-29
4.5.1.2.1 General Troubleshooting and Repair Notes ................................................... 4-29
4.5.1.2.2 PA Functional Testing..................................................................................... 4-30
4.5.1.2.3 Localizing Problems........................................................................................ 4-34
4.5.1.2.4 Isolating Failures............................................................................................. 4-35
4.5.1.2.5 Power Control and Protection Circuitry........................................................... 4-37
4.5.1.3 50 Watt Power Amplifiers ...................................................................................... 4-38
68P81076C25-C
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July 1, 2002