Nautel XR6, Troubleshooting Manual, Page: 93 / 291

XR6/XR3 Troubleshooting Manual Detailed Circuit Descriptions
Issue 3.0 2009-07-15 Page 2-25
• Be applied to the cathodes of CR26, CR28, CR40 and CR42 as a logic true reset command.
The PDM input to all four low PA volts detectors will effectively be clamped to ground for
the duration of the reset pulse. Any low PA volts detector which was latched in its fault state
will be reset.
Alarm indicators
The RF drive control PWB contains lamps (LEDs) which are visible through the RF power module's
front panel. The dc voltage for all alarm lamps is applied through transistor Q7's base-emitter resistor
R98. When an alarm lamp is turned on, the resultant current flow through R98 will forward bias Q7
and turn it on. A nominal 13 V will be applied to J3-12 as a logic true
PM Fault output.
Manual rf drive tuning
See electrical schematic Figure SD-19.
The manual RF drive tuning assembly contains two variable inductors (L1 and L2) which are
connected to form two poles of the RF drive's tuned circuit. Their inductance is determined by the
positioning of their moveable cores. When the RF drive screw is turned clockwise, the inductance of
the inductors decreases. See
“RF drive tuning check” on page 1-36 for information on manually
tuning an RF power module.
RF power blocks
See electrical schematics Figures SD-19 and SD-20.
There are four identical RF power blocks. Each utilizes one quarter of the modulator input/output
PWB (A14), a modulator assembly, a modulator filter, PA input/output PWB and two RF amplifiers.
The RF power blocks (A/B and C/D) are connected in parallel. See Figures SD-19 and SD-20 to
determine which assemblies are associated with a specific RF power block.
Modulator stage
See electrical schematics Figures SD-19 and SD-20.
The modulator stage contains the modulator input/output PWB, four modulators, and four
modulator filters. The function of each modulator is to act as a voltage regulator between the B+
voltage and the power MOSFETs in its associated RF amplifiers. The voltage control is provided by
the carrier level/modulation envelope information on the PDM inputs.