Nautel XR6, Руководство по устранению неисправностей, Страница: 70 / 291

XR6/XR3 Troubleshooting Manual Detailed Circuit Descriptions
Page 2-2 Issue 3.0 2009-07-15
Ac supply voltage
The Ac Power input (J4-21) is an unregulated dc voltage that is proportional to the ac source. The
input is filtered and compared to the low ac ref fault threshold on operational amplifier U4C. If the
Ac Power voltage is below this threshold, the ac low signals switch to 0 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. The transmitter's RF output turns off (shuts back) and remains off until the ac
power returns to an acceptable voltage. The system diagram's
AC Mains
lamp displays a fault
condition. An Ac Sample signal is applied to ADC U9 for application to the diagnostic display.
Reflected power monitor
The Refld Pwr Sample input (J1-5) is a dc voltage that is proportional to the reflected power at the
transmitter's output. The input is filtered and buffered by operational amplifier U1B and associated
components, 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 fault
threshold 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 the
refld_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 pulse
is 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
lamp
displays a fault condition. A Refld Pwr Sample signal is applied to ADC U9 for application to the front
panel's diagnostic display.
Turning off the RF output reduces the refld pwr sample input to 0 V. The Carrier Ref (A) output is
restored to its pre-shutback levels, the Shutback A and B outputs return to open collector, and the RF
output is restored at an exponential rate. If the fault threshold is exceeded before the pre-set power
level is reached, the shutback cycle is repeated. If three or more shutback cycle clock pulses are
applied within any five second period, the
Carrier Ref (A) output is cut back (reduced) until the carrier
level is cut back to a level that results in an acceptable reflected power. When the transmitter enters
cutback mode, the system diagram's
Output Network
lamp flashes on and off. When the refld pwr
sample input returns to or is maintained at a level which is less than the fault threshold, the Shutback
outputs returns to open collector but the system diagram's
Output Network
lamp continues to
display a fault as a maintenance aid. The lamp remains on until reset by the diagnostic display menu.
Sample monitoring circuits
Various parameters are applied to the control/display PWB for local (via the front panel's diagnostic
display) and/or external (via the remote interface PWB) monitoring. In most cases, these parameters
also have associated alarm detection circuitry, but it is not resident on the control/display PWB.