Service manual

RC2000 Service Manual Chapter 2 Theory of Operation 12
Research Concepts, Inc; 10679 Widmer; Lenexa, Kansas; USA 66215 WWW.RESEARCHCONCEPTS.COM
2.2.7 Signal Strength Input Circuits
The RC2000 accepts 2 analog voltages proportional to received signal strength. The controller will use the
strongest signal. The signal strength inputs are normally connected to the AGC (automatic gain control)
output of a satellite receiver. Each channel has an offset and gain adjustment. The purpose of these
adjustments is to expand the range of the AGC signal output by the receiver for measurement by the micro-
controller.
The micro-controller has an 8 channel 10 bit A/D converter which converts voltages in the range of 0 to 5
volts. The range of inputs accepted by the signal strength input circuits is 0 to 10 volts. The first op amp in
each circuit is operated in a voltage follower mode. R40 and R45 form a voltage divider. If a greater input
voltage range is required a series resistor can be placed on the input. Potentiometer P4 adjusts the gain
and potentiometer P3 sets the offset. Components R45, R35, C40, and C41 provide a single stage input
filter with a time constant of 39 msec.
2.2.8 RS-422 Serial Port
U13 and U14 are RS-422 transceivers. RS-422 uses a differential signals of 0 or 5 volts. The transmit pins
of the RS-422 port are tri-stated when the RC2000 is not transmitting. These features allow many RS-422
devices to be daisy chained together. The transmit enable function is implemented using PC.2 of the 82C55.
The data format is 7 data bits with even parity and 1 stop bit at user selectable data rates up to 9600 baud.
2.2.9 Polarotor Drive Circuit
The polarotor drive is implemented using FET Q1. The polarotor has its own separate 5.7-volt supply
implemented using VR2. VR2 is a 5-volt regulator. R30 and R31 form a voltage divider which maintains
the GND terminal of the voltage regulator at 0.7 volts.
2.2.10 5 Volt Power Supply
VR1 is a 5-volt switching power supply which provides power to the digital board. The input to the voltage
regulator is a center tapped 18-volt transformer secondary.
2.2.11 Parts List
The following pages contain the parts list for the RC2000 digital board.
Bill of Materials…RC2KDIG2.S01
Quantity Type Value Ref. Designators
1 27C512 U4
1 5C032 U2
2 5c060 U10,U9
2 75ALS176 75ALS176 U13,U14
1 8097BHN U1
1 82C55 U8
1 BAT DL2450 B1