HYT TC-446 Service Manual

www. hy t. c om . cn

－ 1 －

Content

General… … … … … … … … … … … … … … … … … … … … … … … … … … … … … 2

Brief Introduction… … … … … … … … … … … … … … … … … … … … … … … … ..3

Software Description… … … … … … … … … … … … … … … … … … … … … … ..4

Circuit Description… … … … … … … … … … … … … … … … … … … … … … … ..8

CPU Pins… … … … … … … … … … … … … … … … … … … … … … … … … … … … 12

Part List 1… … … … … … … … … … … … … … … … … … … … … … … … … … … ..14

Adjustment Description… … … … … … … … … … … … … … … … … … … … … .26

Troubleshooting chart… … … … … … … … … … … … … … … … … … … … … … 29

Disassembly and Assembly… … … … … … … … … … … … … … … … … … ..42

Exploded View… … … … … … … … … … … … … … … … … … … … … … … … ..45

Part List 2… … … … … … … … … … … … … … … … … … … … … … … … … … … .46

Packing… … … … … … … … … … … … … … … … … … … … … … … … … … … … ..48

PC Board View… … … … … … … … … … … … … … … … … … … … … … … … … .49

Block Diagram… … … … … … … … … … … … … … … … … … … … … … … … … ..50

Schematic Diagram… … … … … … … … … … … … … … … … … … … … … … ..51

Specifications… … … … … … … … … … … … … … … … … … … … … … … … … 52

TC- 446 Service Manual

－ 2 －

General

 Manual Scope

This manual is intended for use by experienced technicians familiar with similar types of
communication equipment. It contains all service information required for the equipment and is
current as of the publication date.

 User Safety Information

The following precautionsare recommended for personnel safety:

 DO NOT transmit until all RF connectors are verified secure and any open connectors are

properly terminated.

 SHUT OFF and do not operate this equipment near electrical blasting caps or in an explosive

atmosphere.

 When in vehicles with an airbag, do not place a portable radio in the area over an airbag or in the

airbag deployment area.

 Do not expose the radio to direct sunlight for a long time nor place it close to a heating source.
 Do not use any portable radio with a damaged antenna. If a damaged antenna comes into contact

with your skin, a minor burn may result.

 When transmitting with a portable radio, hold the radio in a vertical position with its microphone

about 5 centimeters away from your mouth.

 If you wear a portable radio on your body, be sure to keep the antenna at least 2.5 centimeters

away from your head or body when transmitting.

 This equipment should be serviced by qualified technicians only.

TC- 446 Service Manual

－ 3 －

Brief Introduction

(1)

(3)

(4)

(6)

(5)

(7)

(9)

(8)

(2)

(10)

(11)

(12)

(13)

1. Antenna

2. LED indicator

The light will glow red during transmission. The light will glow green during receiving. During
transmission, the light flashes red when the battery voltage is low.

3. Channel selector knob

Turn the channel selector knob to select from channels 1-16 (Channel 16 can be programmed by
your dealer as scan function).

4. Power/Volume control knob

Rotate the Power/VolumeKnob clockwise until a “click”is heard to turn the radio on, fully counter
clockwise until a “click”is heard to turn the radio off. When the radio is on, turn the knob to adjust
volume.

5. PTT key

Press and hold PTT key to talk, release to receive.

6. Monitor key

In receive mode, long press(above 2 seconds) Monitor key to monitor activity on the current
channel.

7. Microphone

8. Speaker

9. External jack

Remove the jack cover and insert an earphone; or insert programming cable into the jack to
programme the radio via programming software.

10. Battery

11. Belt clip

Used to clip radio on your belt.

12. Battery latch

Used to fasten and remove the battery.

13. Charging connectors

Connect the charging connectors with that on the charger to begin charging.

TC- 446 Service Manual

－ 4 －

Software Specification

 Radio Feature Description

1. Use channel selector knob to choose from 15+1(Scan) channels

2. Monitor

3. CTCSS/CDCSS
Non-standard Model (Other): 38+83 groups

4. Channel Spacing

12.5KHz Narrow Optional

5. Channel Scan (Priority channel and scan revert channel available)

6. Battery Save feature (Dealer programmable)

7. Time-out Timer (TOT)

8. Squelch Level Control (9 levels)

9. Low Battery Alert

10. Model Set Mode

11. PC Programming and Adjusting Mode

12. User Wired Clone Mode

13. Factory Wired Clone Mode

14. Manual Adjust Mode

 Radio Modes

1. User Mode:

User mode is conventional communication mode. Turn the power on while disconnecting the two SELF points, the
radio enters user mode. (Refer to “TC-446 Owner’s Manual”for details about operation in this mode.)

2. Model Set Mode

(1) If the radio is standard model, short out the two MS2 points on PCB and then operate following the steps (3) (5) and

(6). If the radio is non-standard model, please disconnect the two MS2 points on PCB and then operate the
following steps.

(2) To select MS1 (See the initial data table) according to the radio model, if MS1 is 1, short out the two MS1 points on

PCB and continue the following operation. If not, disconnect the two MS1 points and continue.

(3) Short out the two SELF points on PCB and then turn the power on. Two beeps sound.
(4) Turn channel selector knob to the corresponding position (1-11) according to the radio model (Refer to the initial

data table).

(5) Press PTT key while holding down MONI key to set the model. Channel data and settings are initialized (Refer to

the initial data table).

(6) Turn off the power and then disconnect the two SELF points on PCB to complete the model setting.
Take TC-446 (446.00625~446.09375MHz) as example. From the initial data table, it is of standard model. Toinitializeits
model and channel data, you can operate as following:
(1) Short out the two MS2 points on PCB;
(2) Short out the two SELF points. Power on and two BEEP sounds will be heard.
(3) Press PTT key while holding down MONI key. Channel data and settings are initialized (refer to the initial data table).

TC- 446 Service Manual

－ 5 －

(4) After data reset, turn off the power, disconnect the two SELF points and restart the power to use the radio.
Remarks: The old data (frequency, CTCSS/CDCSS, channel function settings) will be changed once the model is set,
and part of functions will also be changed. Therefore, do not make this operation unless it’s very necessary, such as
changing the EEPROM, etc.

3. PC Programming Mode

The following parameters can be set through programming software:

（1） Receive frequency and transmit frequency
（2） Receive signaling and transmit signaling
（3） Busy channel lockout
（4） Time-out timer
（5） Squelch level
（6） Battery save
（7） Audio alarm
（8） Monitor mode
（9） Scan mode
（10） Scan revert channel
（11） Priority scan channel
（12） N/W Model
（13） low power
（14） N setting

4. PC Adjusting Mode

The following parameters can be set via PC programming software:
(1) Low battery alert level
(2) Squelch level 9
(3) Squelch level 3
(4) CTCSS deviation (narrow)
(5) CDCSS deviation (narrow)

5. Manual Adjust Mode

If manual adjust mode is enabled, turn on the power while holding down PTT and MONI simultaneously,the radio enters
manual adjust mode after 2 seconds. Choose the adjusting items by turning the channel selector knob to CH1-CH5
position; use PTT (upwards) or MONI (downwards) to adjust (Note: MIC jack shouldn’t be connected with external cable
while adjusting), CH1-CH5 positions are defined as follows:
(1) Low battery alert level
(2) Squelch level 9
(3) Squelch level 3
(4) CTCSS deviation (narrow)
(5) CDCSS deviation (narrow)

Note:

To enable or disable manual adjust mode: short out the two SELF points, turn on the powerto enter model set mode. And
then the manual adjust mode is enabled. Press [PTT], manual adjust mode is disabled. This mode is suggested to be
disabled after the adjustment is completed.

TC- 446 Service Manual

－ 6 －

6. User/Factory Wired Clone Mode

Turn on the power while holding down MONI, the radio enters wired clone mode.
(1) If the two SELF points are disconnected, press MONI again to begin user wired clone and red LED blinks; When

cloning is completed, red LED goes out.

(2) If the two SELF points are short circuit, press MONI again to begin factory wired clone and red LED blinks; When

cloning is completed, red LED goes out.

Note: The difference between user wired clone mode and factory wired clone mode is that the latter is able to clone
tune parameters.

TC- 446 Service Manual

－ 7 －

 Initial data table

Note: For standard model, CTCSS isoff inall channels after initialization.

MS1 Model

Frequency (MHz) IF (MHz)

1CH 2CH 3CH 4CH 5CH 6CH 7CH 8CH 9-16CH

Tx

(MHz)Rx(MHz)Tx(MHz)Rx(MHz)Tx(MHz)Rx(MHz) (MHz) (MHz) (MHz) (MHz) (MHz) (MHz)

Standard 446.00625~446.09375 -21.4 446.00625 446.00625 446.05625 446.05625 446.03125 446.03125 446.08125 446.01875 446.06875 446.04375 446.09375

CH QT/DQT OFF OFF OFF OFF 97.4 97.4 71.9 79.7 67 85.4 023

TC- 446 Service Manual

－ 8 －

Circuit Description

1. Frequency Configuration

The receiver utilizes double conversion superheterodyne. The first IF is 21.4MHz and the second
is 455KHz. The first local oscillator signal is supplied from PLL circuit. Frequency needed in the
transmitter is supplied from PLL circuit. Figure 1 shows the frequency configuration.

Frequency Range: 446.00625 MHz— 446.09375MHz

Figure 1 frequency configuration

2. Receiver

The receiver utilizes double conversion superheterodyne.

1) Front-end RF Amplifier
The input signal from antenna is amplified in RF amplifier (Q27) after passing through
the receive/transmit switch circuit and a 3-stage LC band pass filter. The amplified
signals are filtered by a band pass filter (a 3-stage LC BPF) to eliminate unwanted
signals before they goes to the first frequency mixer.

Figure 2 receiver section configuration

TC- 446 Service Manual

－ 9 －

2) The First Mixer
The signal from RF amplifier is mixed with the first local oscillator signal from PLL frequency
synthesizer in the first mixer (Q23) to generate a 21.4MHz first IF signal. The first IF signal is then
fed through two monolithic crystal filters (XF1) to remove spurious signals from adjacent channels.

3) IF Amplifier
The first IF signal is amplified in Q22 and then enters the IF process chip IC1. The signal is mixed
with the second local oscillator signal in IC1 to create a 455KHz second IF signal. The second IF
signal is then fed to a 455KHz ceramics filter (CF1) to eliminate unwanted signals before it is
amplified and FM detected in IC1.

4) AF Amplifier
The demodulated AF signal obtained from IC1 is amplified in IC7 (1/4), and then filtered by low
pass filter Q19 and high pass filter Q20, and then de-emphasized by R130 and C156. The
resulting AF signal passes through a volume control circuit and then is amplified to a sufficient
level to drive the speaker by AF power amplifier (IC8).

5) Squelch
Part of the AF signal from IC1 enters IC1 again, and the noise component is amplified and
rectified by a filter and an amplifier to produce a DC voltage corresponding to the noise level. The
DC signal from IC1 goes to the analog port of the microprocessor (IC11). IC11 determines
whether to output sounds from the speaker by detecting whether the input voltage is higher or
lower than preset value.
To output sounds from the speaker, IC11 sends a high level signal to the MUTE and AFCO lines
and turns IC8 on through Q12.

DET

FM IF IC1

IF AMP

HPF

AMP

IC7

AF

LPF

HPFDET

2

39 40 1

SW

Q12

SW

AF/PF AMP

IC7

LPF

IC11
MCU

BUSY

MUTE

AFCO

TI

IC8

SP

Figure 3. AF amplifier and squelch circuit

TC- 446 Service Manual

－ 10 －

6) Receivesignaling
CTCSS/CDCSS
Audio frequencies over 300Hz of the output signal from IC1 is cut off by a low-pass filter. The
resulting signal enters the microprocessor IC11. IC11 determines whether the CTCSS/CDCSS
matches the preset value and controls the MUTE and AFCO and the speaker sound output
according to the squelch results.

3. PLL Frequency Synthesizer

PLL circuit generates the first local oscillator signal for reception and the RF signal for
transmission.

1) PLL Circuit

The step frequency of PLL circuit is 2.5KHz or 6.25 KHz. A12.8MHz reference
oscillator signal is divided at IC2 by a fixed counter to produce a 2.5 KHz or 6.25 KHz
reference frequency. Output signal from voltage control oscillator (VCO) passes
through buffer amplifier Q14 and is divided at IC2 by the dual-module programmable
counter. The divided signal is compared in the phase comparator IC2 with the 2.5 KHz
or 6.25 KHz reference signal. The output signal from phase comparator is filtered
through a low-pass filter and passed to the VCO to control the oscillator frequency.
(See figure 4)

Figure 4 PLL circuit

2) VCO
The operating frequency is generated by Q16 in transmit mode and by Q8 in receive
mode. The operation frequency generates a voltage through the phase comparator to

control the varactor diodes, so as to keep the oscillator frequency consistent with the
preset frequency in CPU (D2 and D3 in transmit mode and D7 and D8 in receive mode).
T/R pin is set high in receive mode causing Q6 to turn off Q16 and turn Q7 on. The T/R pin is set
low in transmit mode. The output from Q8 and Q16 is amplified by Q14 and sent to the buffer
amplifier.

TC- 446 Service Manual

－ 11 －

4. Transmitter

1) Transmit audio

The audio signal from microphone is amplified through IC3, and then pre-emphasized , and
then filtered by another low-pass filter（separate filter）(Q25 and Q24) to eliminate the
frequencies over 3KHz. The resulting signal enters the VCO for direct FM modulation. (See
figure 5)

2) CTCSS/CDCSSEncoder

The necessary frequency for CTCSS/CDCSS encoder is generated by IC11 and
FM-modulated to the PLL reference signal. Since the reference OSC does not modulate the
loop characteristic frequency or higher, modulation is performed at the VCO side by splitter.
(See figure 5)

Figure 5 transmitCTCSS

3) RF amplifier

The transmit signal obtained from VCO buffer amplifier Q14 is amplified by Q15 and Q17.
This amplified signal is passed to power amplifier Q32 and Q31, and is capable of producing
a 4.0W RF power.

4) Antenna Switch and LPF

The RF amplifier output signal is passed through a low-pass filter network and a
transmit/receive switch circuit before it is passed to the antenna terminal. The
transmit/receive switch circuit is comprised of D11 and D12. D11 and D12 is turned on in
transmit mode and off in receive mode.

5. Power

The 5V reference power supply for the control circuit is derived from an internal battery. The
reference power provides a 5V supply in transmit mode [T_V], a 5V supply in receive mode [R_V],
and a 5V supply shared in both modes based the control signal from the microprocessor.

6. Control System

The IC11 CPU operates at 7.3728MHz.

TC- 446 Service Manual

－ 12 －

CPU Pins

PIN No. PIN NAME I/O DESCRIPTION

1 TI I CTCSS/CDCSS input
2 BUSY I Input busy signal
3 BATT I Detect battery voltage
4 TIBI I CTCSS/CDCSS exterior circuit central point input
5 NC
6 SAVE O Power saving control H: OFF L: ON
7 TXLow O Transmitter power control H: Low power L: High power
8 NC

9 DAT O data output
10 CLK O clock output
11 LE O PLL IC enable
12 BEEP O Beep output
13 SCL O E2PROM clock cable
14 SDA I/O E2PROM data cable
15 MUTE O MIC mute control H: Mic mute L:Mic enable
16 MS1 I Model set
17 GREEN O Green light control H: light
18 RED O Red light control H: light
19 TXD O RS-232C output
20 RXD I RS-233C input
21 PTTK I PTT key input
22 MS2 I Standard model select H: Non-standard L: Standard
23 RXC O Receiver power control L: power on
24 NC
25 RESET I Reset input
26 SELF I Self-program L: on
27 TXC O Transmitter power control H:on
28 X

IN

I Oscillator input

29 X

OUT

O Oscillator output
30 Vss I Grounding
31 R/T O TX/RX control H：RX L： TX
32 UL I PLL unlock detector H: Lock L: unlock
33 IF-SELECT I IF select H: 21.4MHz L: 45.05MHz
34 MONIK I MONI key input
35

ENC0

I Channel selector knob encode input

36 ENC1 I
37 ENC2 I

TC- 446 Service Manual

－ 13 －

38

ENC3

I

39 AF

MUTE

O Audio muting control
40 AFP O Audio power control
41 TONE5 O CTCSS code output
42 TONE4 O CTCSS code output
43 TONE3 O CTCSS code output
44 TONE2 O CTCSS code output
45 TONE1 O CTCSS code output
46 TONE0 O CTCSS code output
47

WNTC

O W/N L: Wide H: Narrow

47-70 NC

71 Vcc I Power input:5V
72 V

REF

I A-D converse reference voltage

73 Avss I A-D GND

74-77 NC

78 NC
79 NC
80 NC

TC- 446 Service Manual

－ 14 －

Part List 1

No. P/N Material Name Qty. Ref. No. Address

1 3001051830000 Chip resistor 0402 18KΩ J 1/1 1 R622 B3I
2 3001060000000 Chip resistor 0603 0Ω J 1/10W 16 C23 B3F
3 D20 T1D
4 L3 B3H
5 Q41 T3F
6 R106 T3F
7 R107 B3B
8 R108 B3E

9 R110 T4G
10 R151 B5E
11 R192 B4E
12 R194 B3F
13 R197 B4F
14 R202 B2B
15 R508 B5B
16 R601 B1E
17 R602 B3C
18 3001061000000 Chip resistor 0603 10Ω J 1/10 6 R112 T3E
19 R113 T5J
20 R164 B2C
21 R196 B4G
22 R80 B2D
23 R82 B4G
24 3001061010000 Chip resistor 0603 100Ω J 1/1 6 R127 B5F
25 R147 B4E
26 R74 B2C
27 R75 B4J
28 R76 B5E
29 R90 T5H
30 3001061020010 Chip resistor 0603 1KΩ J 1/10 12 R203 T2E
31 R39 B3B
32 R51 B1F
33 R52 T3F
34 R53 B2D
35 R56 B2B
36 R57 B5B
37 R58 T4B
38 R59 T3B
39 R60 T2D
40 R61 T2D
41 R89 T4I
42 3001061030010 Chip resistor 0603 10KΩ J 1/1 10 R100 T4B
43 R204 T2G
44 R36 B4B

TC- 446 Service Manual

－ 15 －

Part List 1

No. P/N Material Name Qty. Ref. No. Address

45 R37 T2E
46 R38 B2A
47 R40 B3F
48 R41 T5F
49 R42 T5E
50 R44 B2I
51 R45 B2I
52 3001061040010 Chip resistor 0603 100KΩ J 1/ 15 R10 B4C
53 R12 B4B
54 R13 B3D
55 R15 B3D
56 R175 T2B
57 R176 T2B
58 R18 T2C
59 R35 T2C
60 R623 B4E
61 R624 B4F
62 R625 B3E
63 R626 B3F
64 R7 B4B
65 R8 B2E
66 R9 B1D
67 3001061050010 Chip resistor 0603 1MΩ J 1/10 2 R109 T2B
68 R116 T3B
69 3001061230000 Chip resistor 0603 12KΩ J 1/1 2 R170 B1D
70 R617 B4H
71 3001061240010 Chip resistor 0603 120KΩ J 1/ 3 R11 B3B
72 R124 T3F
73 R72 B2D
74 3001061510000 Chip resistor 0603 150Ω J 1/1 2 R68 B2E
75 R69 B2C
76 3001061520000 Chip resistor 0603 1.5KΩ J 1/ 3 R48 B3E
77 R50 T5F
78 R55 T2E
79 3001061530010 Chip resistor 0603 15KΩ J 1/1 3 R161 T4F
80 R162 T4G
81 R163 T4F
82 3001061540000 Chip resistor 0603 150KΩ J 1/ 5 R139 B4B
83 R14 B3D
84 R140 B4A
85 R141 B4A
86 R142 B4A
87 3001061820000 Chip resistor 0603 1.8KΩ J 1/ 2 R131 T4E
88 R144 B3C