Nautel XR12 Troubleshooting Manual

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

Contents

XR12 Troubleshooting Manual Detailed Circuit DescriptionsPage 2-2 Issue 3.0 2009-07-28Alarm threshold circuitsCertain parameters that are monitored by the control/display PWB can initiate an alarm indicationand appropriate transmitter control if an out of tolerance condition occurs.Ac supply voltageThe Ac Power input (J4-21) is an unregulated dc voltage that is proportional to the ac source. Theinput is filtered and compared to the low ac ref fault threshold on operational amplifier U4C. If theAc Power voltage is below this threshold, the ac low signals switch to 0 V. The Carrier Ref (A) outputclamps to 0 V and the Shutback (A) (J7-1) and (B) (J7-2) outputs switch to 0 V and inhibit the exciter'smodulator drive. The transmitter's RF output turns off (shuts back) and remains off until the acpower returns to an acceptable voltage. The system diagram's AC Mains lamp displays a faultcondition. An Ac Sample signal is applied to ADC U9 for application to the diagnostic display.Reflected power monitorThe Refld Pwr Sample input (J1-5) is a dc voltage that is proportional to the reflected power at thetransmitter's output. The input is filtered and buffered by operational amplifier U1B and associatedcomponents, and then applied to the remote interface PWB via the external serial interface(microcontroller U22). The signal is also compared to a pre-determined refld pwr shtbk ref faultthreshold on operational amplifier U4A. When the peak reflected power exceeds a 1.5:1 VSWR(based on rated forward power), the refld pwr sample input exceeds the fault threshold and therefld_pwr_shutback signal switches to 5 V. The Carrier Ref (A) output clamps to 0 V and the Shutback(A) (J7-1) and (B) (J7 2) outputs switch to 0 V and inhibit the exciter's modulator drive. A clock pulseis also applied to an alarm count/cutback circuit in complex programmable logic device (CPLD)U18. The RF output is instantly shut back (turn off). The system diagram's Output Network lampdisplays a fault condition. A Refld Pwr Sample signal is applied to ADC U9 for application to the frontpanel's diagnostic display.Turning off the RF output reduces the refld pwr sample input to 0 V. The Carrier Ref (A) output isrestored to its pre-shutback levels, the Shutback A and B outputs return to open collector, and the RFoutput is restored at an exponential rate. If the fault threshold is exceeded before the pre-set powerlevel is reached, the shutback cycle is repeated. If three or more shutback cycle clock pulses areapplied within any five second period, the Carrier Ref (A) output is cut back (reduced) until the carrierlevel is cut back to a level that results in an acceptable reflected power. When the transmitter enterscutback mode, the system diagram's Output Network lamp flashes on and off. When the refld pwrsample input returns to or is maintained at a level which is less than the fault threshold, the Shutbackoutputs returns to open collector but the system diagram's Output Network lamp continues todisplay a fault as a maintenance aid. The lamp remains on until reset by the diagnostic display menu.