Nautel XL12 Technical Instructions

Contents

12 000 WATT AM BROADCAST TRANSMITTERXL12Page 6-1301 January 20026.7.4 DC POWER SUPPLY MONITOR PWB(see figure SD-12): The DC power supply monitorPWB (A29) provides LEDs and test points formonitoring the status of the transmitter's criticaloperating voltages. It also contains circuitry whichmonitors AC power status and, if necessary,generates an alarm signal for the control/monitorfunction6.7.4.1 AC Fail Detector: The AC fail detectormonitors the Z secondary of the AC powertransformer to determine loss of a line and/or ACmains. A sample of the AC is applied to diodebridge CR4/CR6/CR8/CR10/CR11/CR12 throughresistors R1/R2/R3. This voltage is smoothed bycapacitor C1 and regulated to 24 VDC relative toreference point 1, by resistors R8/R9, zener diodeCR16 and capacitor C3. This regulated 24 VDCsupplies power to the AC fail detector circuitry. Anadjustable AC FAIL THRSHLD bias voltage developedby resistors R10/R11/R12 enters the non-invertinginput of op-amp U1/A.A sample of the AC is also applied to diode bridgeCR5/CR7/CR9/CR13/CR14/CR15 thru resistorsR4/R5/R6. This sample voltage is smoothed bycapacitor C2 and resistor R13 and is used as a DCsample proportional to the level of the AC mainsvoltage at the inverting input (pin 2) of U1/A. Whenthis DC reference voltage is higher than the AC FAILTHRSHLD bias voltage at U1/A-3, the output atU1/A-1 will be low (near reference point 1). Thisoutput will be applied to the inverting input (pin 6) ofop-amp U1/B.A bias voltage is established at the non-invertinginput to U1/B (nominally 3 VDC relative toreference point 1) by resistors R19 and R20. Whenthe voltage at U1/B-6 falls below the bias voltage atU1/B-5, the output at U1/B-7 will be high (nearreference point 1). AC FAIL ALARM lamp DS1 will beoff and the base of transistor Q1 will be drivenenergizing relay K1.When the DC reference voltage at U1/A-2 fallsbelow the AC FAIL THRSHLD bias voltage at U1/A-3,due to a loss of an AC line or low AC mains, theoutput at U1/A-1 will go high (+24 VDC relative toreference point 1). This high output will be applied tothe inverting input U1/B-6 and cause the output atU1/B-7 to go low (near reference point 1). AC FAILALARM LED DS1 will turn on and Q1 will turn off de-energizing relay K1. A 5.1 VDC AC fail signal willbe applied to J1-7 for use in the control/monitorfunction.