Nautel XR12 Troubleshooting Manual

Also see for XR12: Installation manual Operation and maintenance manual Preinstallation manual

Contents

XR12 Troubleshooting Manual Responding to alarmsPage 1-28 Issue 3.0 2009-07-28PA volts to ground impedanceMeasure impedance between the PA volts and ground for each RF power block:1. Measure resistance between terminal H (PA volts input) of each PA input/output PWB andground, using a digital multimeter.2. Each of the resistance measurements in Step 1 should be a nominal 77 kΩ. If allmeasurements are satisfactory, proceed to “PA volts to B+ impedance” on page 1-29.3. If any resistance measurement in Step 1 is less than 77 kΩ, disconnect connector P1 from J1of the RF drive control PWB and repeat the resistance measurement.4. Each resistance measurement in Step 3 should be open circuit. If they are now satisfactory,an impedance problem exists in the RF drive control PWB's PA volts circuit.5. If a resistance measurement in Step 4 is not satisfactory, sequentially remove the modulatorassembly and both RF amplifiers associated with the suspect RF power block (see Table 1.3on page 1-27) and note the resistance measurement as each assembly is removed.• If a resistance measurement indicates an open circuit after the removal of an assembly,do not remove any additional assemblies. Assume the last assembly removed is defective.• Reinstall other removed assemblies (if any) for the RF power block being tested and notethe resistance measurement as each assembly is installed. If the resistance measurementis unacceptable after the installation of an assembly, assume the assembly is defective andreplace it (see “Modulator assembly replacement” on page 1-47 or “RF amplifierassembly replacement” on page 1-48).6. Reinstall removed assemblies, using repaired or serviceable replacement assemblies.• If connector P1 was disconnected from J1 of the RF drive control PWB, reconnect it.CAUTION:The heat sinks of modulator assemblies and RF amplifiers are coated with a filmof thermal compound. Use care to ensure the film does not become contaminatedwith foreign particles.When installing an assembly, visually inspect the mating surfaces of its heat sinkand the module's chassis. Ensure both surfaces are coated with a thin film ofthermal compound. Ensure foreign particles that may affect thermal transfer arenot embedded in the compound.