Motorola Astro Digital Spectra Digital Spectra Plus Basic 6881076c20 E Manual

Chapter 3 Basic Theory of Operation
3.1 Introduction
The following theory will help isolate the problem to a particular board. Using circuit board 
replacement as the basic service approach maximizes the working time of the radio.
3.2 General Overview
The ASTRO Digital Spectra and Digital Spectra Plus radios are wideband, synthesized, fixed-tuned 
radios. The ASTRO Digital Spectra is available with VHF, UHF, and 800 MHz bands. The ASTRO 
Digital Spectra Plus is available with VHF and 800 MHz bands only....

February 3, 20036881076C20-E
3-2Basic Theory of Operation: Analog Mode of Operation
3.3 Analog Mode of Operation
3.3.1 Receive Operation
When the radio is receiving, the signal comes from the antenna/antenna-switch on the power 
amplifier board to the front-end receiver assembly. The signal is then filtered, amplified, and mixed 
with the first local-oscillator signal generated by the voltage-controlled oscillator (VCO). The resulting 
intermediate frequency (IF) signal is fed to the IF circuitry on the...

6881076C20-EFebruary 3, 2003
Basic Theory of Operation: Control Head Assembly 3-3
3.5.2 Display (W9 Model)
The control head assembly for a W9 model has an 11-character, alphanumeric, vacuum fluorescent 
display. It needs three separate voltages to operate: the cathode needs 35V to accelerate electrons 
to the anode; the grid needs 40V to totally shut off current flow; the filament needs 3.8 Vrms at 80 
mA. These voltages are obtained from the transformer on the display controller board.
3.5.3 Vacuum...

February 3, 20036881076C20-E
3-4Basic Theory of Operation: Power Amplifier
3.5.8 Vehicle Interface Port (VIP)
3.5.8.1  Remote-Mount
The VIPs allow the control head to operate outside circuits and to receive inputs from outside the 
control head. There are three VIP outputs that are used for relay control. There are also three VIP 
inputs that accept inputs from switches. See the cable kit section for typical connections of VIP input 
switches and VIP output relays.
The VIP output pins are located on the...

6881076C20-EFebruary 3, 2003
Basic Theory of Operation: Front-End Receiver Assembly 3-5
3.6.2 Power Control
A directional coupler and detector network controls power. It senses the forward power from the last 
gain stage and feeds the detected voltage back to the command board control circuitry, where it is 
compared to a reference voltage set during power-set procedures. The dc feed voltage is corrected 
and supplied to the “controlled” stage of the power amplifier. Circuitry on the power amplifier...

February 3, 20036881076C20-E
3-6Basic Theory of Operation: Voltage-Controlled Oscillator (VCO)
Synthesizing for the first and second VCO is performed by the prescaler and synthesizer ICs. These 
ICs are programmed through a serial data bus from signals generated on the VOCON board. A dc 
voltage, generated on the command board, sets the synthesizer’s reference oscillator frequency of 
16.8MHz. This voltage is controlled by the digital-to-analog converter (D/A), and is the only element 
of the RF board...

6881076C20-EFebruary 3, 2003
Basic Theory of Operation: VOCON (Vocoder/Controller) Board 3-7
The regulator and power control circuits include an unswitched +5V discrete circuit and the regulator/
power control IC, which produces both switched +5V and 9.6V. The unswitched +5V source is used 
as a reference for its switched +5V source. Filtered unswitched +5V is used for the microcontrol 
circuits. Switched +5V and 9.6V are controlled by a digital transistor from the serial input/output IC. 
The power...

February 3, 20036881076C20-E
3-8Basic Theory of Operation: VOCON (Vocoder/Controller) Board
The VOCON board controls receive/transmit frequencies, the display, and various radio functions, 
using either direct logic control or serial communication to external devices. The connector J801 
provides an interface between the encryption module and the VOCON board for encrypting voice 
messages.
The VOCON board executes a stored program located in the FLASH ROM. Data is transferred to 
and from memory by the...

Chapter 4 Test Equipment, Service Aids, and Tools
4.1 Recommended Test Equipment
The list of equipment contained in Table 4-1 includes most of the standard test equipment required 
for servicing Motorola mobile radios, as well as several unique items designed specifically for 
servicing this family of radios. The Characteristics column is included so that equivalent equipment 
can be substituted; however, when no information is provided in this column, the specific Motorola 
model listed is either a...

February 3, 20036881076C20-E
4-2Test Equipment, Service Aids, and Tools: Service Aids and Recommended Tools
Table 4-2 contains a listing of the plug-in elements that are available for the BIRD wattmeters listed in 
the 
Table 4-1.
Table 4-3 contains a listing of non-Motorola test equipment recommended for servicing mobile 
radios.
4.2 Service Aids and Recommended Tools
Refer to the tables in this section for a listing and description of the service aids and tools designed 
specifically for servicing this...