Realistic RadioShack TRC-448 Service Manual
REALISTIC
■
.0
40 - CHANNEL
MOBILE TRANSCEIVER
Catalog Number: 21-1561
00
CUSTOM MANUFACTURED FOR RADIO SHACK A DIVISION OF TANDY CORPORATION
CONTENTS
SPECIFICATIONS
BLOCK DIAGRAM
PRINCIPLES OF OPERATION
DISASSEMBLY
ALIGNMENT PREPARATION
ALIGNMENT POSITIONS AND POINTS
PLL SECTION ALIGNMENT CHART
VCO OUTPUT FREQUENCY, IC-2 INPUT FREQUENCY AND CODE TABLE .......
TRANSMITTER SECTION ALIGNMENT CHART
RECEIVER SECTION ALIGNMENT CHART
ALIGNMENT CONNECTIONS
NOISE BLANKER ALIGNMENT CHART
PLL P.C. BOARD TOP VIEW
PLL P.C. BOARD BOTTOM VIEW
MAIN P.C. BOARD TOP VIEW
MAIN P.C. BOARD BOTTOM VIEW
WIRING DIAGRAM (1)
WIRING DIAGRAM (2)
6 - 8
15, 16
3, 4
9
10
11
13
14
18
19
20
21
22
23
5
9
12
17
LED P.C.BOARD (TOP VIEW)
LED P.C.BOARD (BOTTOM VIEW)
LED P.C.BOARD/ CHANNEL SWITCH P.C.BOARD WIRING DIAGRAM
TROUBLESHOOTING
SEMICONDUCTOR VOLTAGE READINGS
PLL P.C.BOARD ASSEMBLY PARTS LIST
MAIN P.C.BOARD ASSEMBLY PARTS LIST
LED P.C.BOARD ASSEMBLY PARTS LIST
CHASSIS ASSEMBLY PARTS LIST
EXPLODED VIEW
SCHEMATIC DIAGRAM
SEMICONDUCTOR LEAD IDENTIFICATION
IC PIN CONFIGURATION
.. . .
24
24
24
25 27
28 33
ti
34
40 49
49
50
51
52, 53
54
54, 55
39
SPECIFICATIONS
DESCRIPTION
Frequency Tolerance
RF Output
Modulation Distortion
Spurious Harmonic Emission AM
Carrier
Unwanted Sideband Suppression
Current Drain
Modulation Frequency Response
Carrier Power Uniformity
MIC Input Level Uniformity
Intermodulation Distortion
MIC Input Level Uniformity
Microphone Sensitivity
AMC Range
Max. Sensitivity
Sensitivity
AGC Figure of Merit
Overload AGC Characteristics
Overall Audio Fidelity
Cross Modulation RS Standard
Adjacent Channel Selectivity
Maximum Audio Output Power
Audio Output Power
THD
THD
Suppression
AM
SSB
AM
SSB
AM
SSB
SSB
SSB
CONDITION
TRANSMITTER
13.8 V DC
13.8 V DC
80% MOD 1 kHz
2.5 kHz (SSB)
No Modulation (AM)
(SSB)
80% MOD (AM)
10 W PEP Two-Tone (SSB)
1 kHz
0 dB
450 Hz
Lower
Upper
Ch-to-Ch with No MOD
Ch-to-Ch for 4 W Output,
1000Hz Single-Tone
500 and 2500 Hz Two-Tone
LSB/USB 4 W Output
1.5 kHz Single Tone
AM 50% MOD
SSB 4 W PEP
AM
SSB
AM
SSB
10 dB S/N
50 mV 10 dB
10 mV to 100 mV AM
at 6 dB Down
Upper Frequency AM
Lower Frequency AM
AM
10 kHz
AM
SSB
10% THD
500 mW Output 1 mV
Input 30% (MOD)
1 mV Input 1 kHz
Single Tone
2.5 kHz
50 - 100% MOD
10 - 12 W PEP
RECEIVER
80% (MOD)
AM
SSB
AM
SSB
SSB
SSB
SSB
AM
SSB
SSB
AM
NOMINAL
±0.0003%
±0.0003%
3.8 W
(4
watts max.)
12 W PEP
3%
-65 dB
65 dB
-
50 dB
-
-50 dB
1500 mA
1000 mA
2000 mA
2500 mA
AM SSB -6 dB
AM SSB -6 dB
0.3 W
AM
SSB 2 dB
30 dB
1 dB
0.7 mV
0.7 mV
50 dB
20 dB
0.5
µV
0.25 µV
0.5 AV
0.25 AV
90 dB
90 dB
±2 dB
±2 dB
2100 Hz
3500 Hz
300 Hz
300 Hz
60 dB
80 dB
90 dB
5 W
5W
3.5 W
3.5W
3%
5%
3%
LIMIT
±0.005%
±0.005%
3.5 - 4.0 W
10 - 12 W
10°/©
-60 dB
-
60 dB
-40 dB
-40 dB
2000 mA
1500 mA
2600 mA
3000 mA
AM -10 dB SSB -14 dB
AM SSB -10 dB
0.5 W
3 dB
25 dB
3 dB
1.5 mV
1.5 mV
30 dB
10 dB
1 AV
0.50
1 AV
0.5 µV
80 dB
80 dB
±5 dB
-
±5 dB
1750 - 2500 Hz
1750'
150 - 500 Hz
150 - 500 Hz
50 dB
60 dB
60 dB
4 W
4W
3 W
3W
6%
12%
6%
2500 Hz
DESCRIPTION
CONDITION
NOMINAL
LIMIT
RF Gain Control Range at Max.
Sensitivity Level
S/N Ratio
Squelch Sensitivity at Threshold
Squelch Sensitivity at Tight
Skirt Rejection (±20 kHz)
5 Meter Sensitivity at "S-9"
(No Modulation AM)
Image Rejection Ratio
fo + (2 x 7.8 MHz)
1/2 IF Rejection Ratio
fo + 7.8 MHz/2
IF Rejection Ratio 7.8 MHz
Oscillator Drop-out Voltage
Current Drain at No Signal
Current Drain at Maximum
Clarifier Range
Spurious Rejection Ratio
Within Band
Outside of Band
Microphone Sensitivity
Output Power
Current Drain
Frequency Range
Channel
Frequency Control
Operating Temperature
Humidity
Microphone
Operating Voltage
Power Consumption
Meter
Size
.
40 dB
40 dB
40 dB
40 dB
0.5 µV
0.5µV
1000 ptV
1000 /../V
80 dB
100µV
100 ptV
80 dB
80 dB
90 dB
90 dB
90 dB
90 dB
7 V
7V
550 mA
550 mA
1000 mA
1000 mA
±1 kHz
±1 kHz
65 dB
65 dB
60 dB
60 dB
1 mV
3.5 W
500 mA
1000 mA
AM
SSB
Input 1 mV
AM
SSB
AM
SSB
AM
SSB
AM
AM
SSB
AM
SSB
AM
SSB
AM
SSB
AM
SSB
AM
SSB
AM
SSB
AM
SSB
AM
SSB
AM
SSB
PUBLIC ADDRESS
3 W Output 1 kHz
10% Distortion
No Signal
Max. Output Power
GENERAL
29.965 to 27.405 MHz
40 Channels
Crystal Control (PLL System)
°
—10
C to 50
°
C
10 to 95%
Dynamic Type with PTT Switch
13.8 V DC Nominal (12.0 — 15.0 Volt DC)
Pos./Neg. Ground 40 Watts
TX Power and Signal Strength
205(W)
x 60(H) x 260(D) mm (8-1/4" x 2-1/2" x 10-1/2")
30 — 50 dB
30 — 50 dB
35 dB
35 dB
1 /./V
1µV
500 — 2000 µV
500 — 2000 µV
70 dB
50 — 200 µV
50 — 200 µV
65 dB
65 dB
80 dB
80 dB
75 dB
75 dB
10 V
V
1 0
1000 mA
1000 mA
1500 mA
1500 mA
±0.6 — ±2.5 kHz
±0.6 — ±2.5 kHz
56 dB
56 dB
50 dB
50 dB
2 mV
3 W
1000 mA
1500 mA
NOTE:
Nominal Specs represent
design specs: all units should be able to approximate these — some will exceed and
&kr
some may drop slightly below these specs. Limit Specs represent the absolute worst condition which still might
be considered acceptable; in no case should a unit perform to less than within any Limit Spec.
PRINCIPLES OF OPERATION
This section of the Service Manual will give you a brief technical description of unique or special circuits
which you might otherwise not understand, notice or be able to troubleshoot
PLL CIRCUIT
The TRC-448 uses a Digital Phase Lock Loop circuit to synthesize each of the channel frequencies. The
PLL Circuit consists of a reference crystal oscillator (10.24 MHz), reference divider, programable divider,
crystal oscillator, Phase Detector, Low Pass Filter (LPF) and a Voltage Controlled Oscillator (VCO, which
uses a varicap diode as the frequency control source).
Refer to the AM and USB Block Diagram as you go through the following description. A 10.24 MHz
Crystal is used as a reference frequency. The crystal is connected between Pin 4 and 5 of the PLL IC IC-2.
Crystal oscillator Q10 produces a 33.4875/3 MHz frequency signal. This signal is processed through Q11
tripler and mixed by IC-1 mixer with the Q5 VCO frequency (34.7675 to 35.2075 MHz). The resulting
down-mix produces signals of 1.28 through 1.72 MHz, which pass through LPF, and Q12 amplifier and
then applied to Pin 3 of PLL IC IC-2. These frequencies are divided by "N" ,(128 through 172) as
determined by the Channel Selector switch. Thus the output is 10 kHz (divided internally by IC-2).
Also, the reference oscillator frequency, 10.24 MHz, is divided by 1024 (again, internally by IC-2) resulting
in another 10 kHz frequency.
,
.
These two 10 kHz signals are fed to the Phase Detector and AFC. An error voltage is generated by the
Phase Detector which is in proportion to the phase difference between these two 10 kHz signals. This error
voltage appears at Pin 7. The AFC circuit brings the VCO to within the lock range of the Phase Detector.
The AFC output is a tri-state output that is open when the circuit is in phase lock, provides positive going
pulses when the VCO frequency is lower than the reference frequency and provides negative going pulses
when the VCO frequency is higher than the reference frequency. This error voltage appears at Pin 1. The
error voltage which appears at Pin 7 and 1 are the result of the phase difference, plus effects of harmonics
and extraneous noise. These error voltages pass through the LPF, where the error voltage is integrated and
harmonics and noises are filtered out. The resulting DC voltage is applied to the VCO (a varicap diode)
whose capacity varies with applied DC voltage. With proper circuit design and precise adjustments, the
VCO frequency is accurate and precise. When the Phase Detector senses no frequency or phase difference
between the two 10 kHz signals, the system is `locked" and the VCO generates a frequency which is as
accurate and stable as the reference crystal oscillator.
The Channel Selector switch provides a Binary Code output which is connected to Pins 9 through 16. The
resulting code determines "NV', the divisor which produces the required output frequency for each channel
(precisely spaced 10 kHz apart).
For AM Receive Mode, crystal oscillator Q9 generates a frequency of 33.485/3 MHz. This signal is also
processed through Oil tripler and mixed in IC-1 mixer with the Q5 VCO frequency (34.765 to 35.205
MHz). The resulting down-mix produces 1.28 through 1.72 MHz frequencies which are supplied to Pin 3 of
IC-2. Thus, the circuit functions in the same way, except for the method of deriving the required 1.28
through 1.72 MHz stepped frequencies.
For LSB, crystal oscillator Q10 generates a frequency of 33.4875/3 MHz. This signal is processed through
Q11 tripler. Carrier oscillator Q1 produces a 7.8025 MHz signal. This signal is processed through Ti and T2
Band Pass Filter, tuned to the 2nd harmonic (15.605 MHz) and mixed in Q3 mixer with the Q4 VCO
frequency (19.1625 to 19.6025 MHz). The resulting up-mix produces 34.7675 through 35.2075 MHz
which pass through BPF and mixed in IC-1 mixer with the 33.4875 MHz. The resulting down-mix produces
the 1.28 through 1.72 MHz frequencies which are supplied to Pin 3 of IC-2. Thus, the circuit functions in
the same way, except for the method of deriving the required 1.28 through 1.72 MHz stepped frequencies.
--6-
At Pin 8 of IC-2 a Transmit Inhibit signal is available. It provides a high output (supply voltage to IC-2)
when the synthesizer attains a lock condition, or a low (0 volt) when not in lock. When the output is either
high or low, no phase error pulses are outputted that require detection. This circuit is used to inhibit
transmitter operation if the programmed frequency cannot be properly acquired. The lock detector output
will go low if a frequency error exists for more than 0.5 milliseconds. This signal is applied to the base of
Q8, turning it on or off. Thus the Transmitter can not operate in an unlocked condition of the PLL.
The channel selector switch also has an inhibit function, when the selector switch is set in between two
channel positions, Q13 is turned on to kill Q6.
TX: AM USB
RX : USB
RX : AM
OSC
Q10
OSC Q9
33.485/3 MHz
33.4875/3 MHz
CARRIER
011
TRIPLER
0.5V E
OSC Q1
5V
7.8025 MHz
408
1.5V
BPF
A
10.24 MHz
IC-1
MIXER
4
-
L
IC-2
CI
PLL IC
-
r
5
CHANNEL
SWITCH
AM and USB
(Receive and Transmit)
15.605 MHz
4-1
MIXER
BPF
128-
1.72 MHz
LPF
Q12
AMP
k 9-1
Q3 F
-57775
35.2075 MHz
BPF
34.765 -35.2075 MHz
Q5
VCO
LPF
C16, 07
BUFFER
11.1.1.1.71=
OUTPUT
2V
4
INH BIT
Q8
1, 7
8
19.1625 -19.6025 MHz
Q4
r
VCO
eT
INHIBIT
Q13
Q6, Q7
BUFFER
OUTPUT
2V
TX : LSB
RX : LSB
OSC
Q10
33.4875/3 MHz
Q11
TR IPLER
5V1
BPF
10.24 MHz =
IC-1
MIXER
1.28
1.72 MHz
LPF
Q12
AMP
1, 7
IC-2
-
PLL IC
r
CHANNEL
SWITCH
9--1
8
LSB
(Receive and Transmit)
—7—
LPF
INH BIT
Q8
INHIBIT
Q13
AUTOMATIC MODULATION CONTROL CIRCUIT
The Automatic Modulation Control (AMC) circuit consists of Q14, D26, D27 and D24. The Mic input
signal is fed to pin 4 of the microphone jack and then through R62, C84 to the input terminal (pin 5) of
1C-3 where it is amplified and delivered through C90 and VR4 for further amplification by Q15, Q232,
Q233, Q234 and Q235. The Audio amplifier/Modulation amplifier drives T216, whose secondary incorporates C104, through D228 and R280, which couples a portion of the signal to AMC detector diodes
D27 and D28. D26 (an 8-volt zener) is connected to the output of D27/28; when the detected DC voltage
from D27/28 exceeds 8 volts, D26 conducts. This applies a DC voltage to the base of Q14, thus decreasing
its collector impedance. Notice that the combination of Q14 and VR4 automatically sets the desired audio
signal level processed by the audio amplifier circuitry. VR5 is adjusted to seta modulation level of less than
100%.
VR4 is adjusted to set a modulation level in the SSB mode. IC-3 is a silicon integrated circuit which functions as a audio amplifier with built-in automatic voice-operated gain adjustment. It is designed to provide
an essentially constant output signal for a 60 dB range of input.
.
MIC JACK
AUTOMATIC LIMITER CONTROL (TRANSMITTER)/AUTOMATIC GAIN CONTROL (RECEIVER)
The Automatic Limiter Control (ALC) circuit consists of D209, D210 and Q214. The RF output signal is
detected by 0209 and D210. This applies a negative DC voltage to the gate of Q214, thus decreasing its
source voltage. This source voltage controls Q207's (7.8 MHz amplifier) base bias voltage, thus decreasing
its base voltage. This automatically sets the desired RF output level processed by the RF amplifier circuitry.
V R207 is adjusted to set a RF power level of less than 12 watts PEP.
Q214 is also used as an automatic gain control (AGC). AGC circuit consists of Q214, D221 and D222.
The amplified IF signal is detected by D221, D222, D224, and D225. This voltage is used for fast-attack
AGC. D221, D222 and C279 are used for slow-release AGC. Thus, the circuit functions in the same way,
except for the delivering of source voltage. VR206 is adjusted to set a "0
R62
4
7
4
IC3
C90
V
R4
Q14
Q15
D26
K K
D27
C104 R280
VR5
D28
reading on the S-meter.
-
T216
D228
-11Q207
f
VR206
•
Q214
VR207
C279
—8—
T209
D224
D225
L208
D209
D210
777
NOISE BLANKER
Noise pulses are amplified by IC-201 and detected by D236 and D237. The detected pulses are then
amplified by Q226 and Q227. This applies a positive pulse to the base of Q228, thus decreasing its collector
impedance to shunt the Q225 gate impedance during the duration of the noise pulses. The most objectionable noise pulse frequencies are distributed around 40 MHz, thus T213 and T214 are tuned to this
frequency.
RF AMP
Q223, Q224
NOISE
T213
AMP
IC-201
DISASSEMBLY
Refer to Figure 1.
Step 1: Remove two bracket screwsAO and the Bracket.
Step 2: Remove 4 cabinet mounting screws ®
(two from each side).
Step 3: Remove Cabinet Top and Bottom.
MIX
Q225
VV V
BLANKER
Q228
T214
nn
N
NOISE
DET
D236, D237
IF
AMP
Q226, Q227
ALIGNMENT PREPARATION
TEST EQUIPMENT REQUIRED
Oscilloscope
1.
AC VTVM
2.
DC VTVM
3.
4.
Frequency Counter with level meter
AUDIO Signal Generator
5.
Sweep Generator (0 50 MHz)
6.
7.
Power meter (50
8.
50
2, 10
9.
2-tone generator (500 Hz — 2.5 kHz)
10.
RF Signal Generator (0 30 MHz)
Pulse Generator
11.
12.
Monitor Receiver (54 MHz)
(or Spectrum Analyier)
W dummy load
2)
FIGURE 1
ALIGNMENT POSITIONS AND POINTS
PLL SECTION ALIGNMENT CHART
Step
1
2
3
4
5
6
Control Setting
MODE — RX
CH-19
CLARIFIER — Center
MODE — RX
CH-19
MODE — RX (AM)
MODE — RX (LSB or USB)
MODE — RX (LSB)
MODE — RX (LSB)
Test Equipment
DC VTVM
Freq. Counter with
with level meter
See NOTE 1 below
Freq. Counter with
level meter
Freq. Counter with
level meter
Freq. Counter with
level metre
Freq. Counter with
level meter
Test Point or
Connection
Both ends of
VR-304
CLARIFIER
Control
TP-8
TP-5
TP-5
TP-1
TP-2
Adjust
VR -2 for 4V DC
TC-6 for 10.24 MHz
+10Hz
TC-4 for 33.485 MHz
T7, 8 for max. output
TC-5 for 33.4875 MHz
Check the frequency :
7.8025 MHz
TC-1 for 7.8025 MHz
+10 Hz
T1, T2 for max. output
7
8
9
10
11
12
NOTE 1 :
MODE — RX (USB)
CH-1
MODE — RX (LSB)
CH-19
MODE — RX (LSB)
CH-1
MODE — RX (AM)
CH-19
MODE — RX (LSB)
CH-19
MODE — TX (AM or USB)
Steps 2 through 12, connect Frequency Counter through a 10 pF Capacitor to the test point noted.
TEST POINT
UNIT UNDER TEST
DC VTVM
See NOTE 2 below
Freq. Counter with
Level Meter
DC VTVM
See NOTE 2 below
Freq. Counter with
level meter
Freq. Counter with
level meter
Freq. Counter
I 1
10pF
TP-7
TP-3
TP-7
TP-4
TP-4
TP-5
FREQUENCY COUNTER
TC-3 for 2.5 V DC
±0.1 V
T3, T4 34.9875 MHz for
max. output
TC-2 for 2.5 V DC
T6 for max. output
at 34.985 MHz
T5 for max. output
at 19.3825 MHz
VR-1 for 33.4875 MHz
NOTE 2 :
NOTE 3 :
Steps 7 and 9, DC output should change from 2.5 ± 0.1 volts on CH-1 to approx. 3.5 volts on CH-40.
You can check the input frequency to IC-2 at TP-6, use TP-7 for ground.
—11
—
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