Harris Platinum HT EL 2000LS Technical Manual

Harris Platinum HT EL 2000LS Technical Manual Manual pdf 67 page image

Appendix ARF Amplifier Modules, Platinum SeriesA.1 General InformationThis procedure is intended to be used as a guide in isolating faultsand troubleshooting Platinum TV RF power amplifiers withpassive bias.Module faults are most easily verified by swapping the suspectedfaulty module with a known working module in another slot. Ifthe fault follows the module, then the problem is probablyinternal to the module. If the fault remains at the same slot aftersubstituting modules, then the search for the problem shouldprobably focus on the rest of the transmitter system.A.1.1 Factory Module RepairIf a failure of a module occurs, the module may be returned tothe factory for repair.To return a module, contact Harris Repair Department:By phone: 217-222-8200By FAX: 217-224-2840By mail:Harris Repair DepartmentP.O. Box 4290Quincy, Illinois 62305-4290Include the part number and serial number of the module whenrequesting service. Instructions to ship the module will be proc-essed and communicated to you.Please provide as detailed information as possible about thenature of the failure and the operating condition of the moduleat the time of failure. This data will help our Repair Departmentservice your module promptly and efficiently.If you do not stock a spare module and require another unit foroperation, a spare may be obtained as a loaner unit from theHarris Repair Department while your unit is shipped to ourfactory for repair.If you are located within the United States, you will be billed forshipping charges, and if your warranty has expired a nominal feewill be charged for use of the module.If you are located outside the United States, the same loanerservice will be offered wherever feasible, but in addition to anyshipping charges you will be responsible for all import duties,transfer fees or international tariffs.A.1.2 Local Module RepairIf local repair is necessary, the following troubleshooting guideand repair procedures are recommended. We strongly recom-mend reading the appropriate parts of the Theory of Operation,paragraph A.2 before proceeding.Optional PA Module Test Fixture (992-8556-002) is needed forlocal testing or repair. The fixture will allow testing of a PA ordriver module while using the transmitter as the source of DCpower and RF drive.A.2 RF Amplifier Modules Theory ofOperationThree types of RF amplifier modules are used in a Platinum™Series transmitter:• Driver Modules are multiple-stage, high gain RF amplifiersused primarily to amplify an exciter output and drive sub-sequent amplifier stages.• 525 Watt PA Modules are built in driver module configura-tion. High band modules are biased class A for the twoseries configured quarter modules and class AB for the twoparallel output quarter modules.Low band modules are biased class A for the first quarter moduleand class AB for the two parallel output quarter modules.525 Watt PA modules have a polarizing key on the opposite sidefrom driver modules. This will prevent interchanging of driverand 525 Watt PA modules. Due to the differences between 525Watt PA’s and drivers in bias, gain matching pads and theadjustment of the protection circuitry they are not interchange-able without complete testing and readjustment of the protectioncircuitry.• PA Modules are single-stage, high-power, high-efficiencyamplifiers which use four parallel amplifiers to achieveoutput power levels in excess of 1 kW each.Both drivers and PAs share some common features. Drivers andPAs both contain smaller amplifier subassemblies called “quartermodules.”A multi-pin connector on the rear of each module feeds RF drive,50 Volts DC, and ENABLE commands to the module, and passesa fault status signal back to the slave controller. RF output ispassed through a separate coaxial connector. The rear panels ofdrivers 525 Watt PAs and 1 kW PAs are keyed differently, so thatlower power units cannot be plugged into PA slots.The modules are “hot-pluggable,” meaning that they can beremoved or inserted during transmitter operation without turningthe transmitter off. A disable switch is located in the front handleof each module for this purpose.The modules protect themselves by automatically disablingthemselves if an improper operating condition is detected. Aprotection, control, and monitor (PCM) system monitors themodule’s operating conditions. If all of the conditions are accept-able, upon an ENABLE signal from the slave controller, the PCMsystem will enable the module. If a fault condition arises or theENABLE signal is interrupted, the PCM system disables themodule by shutting off the 50 Volts DC.Descriptions of the various subsystems of Platinum modules aregiven below. First, the RF signal paths of the modules are traced;then, the subsystems are described in more detail.Refer to the cover sheet of the drawing package for your trans-mitter to locate the necessary drawing numbers for the modulesand subassemblies.888-2457-001 A-1WARNING: Disconnect primary power prior to servcing.