HYT TC-780 User manual

Contents
General ...............................................................................................................................1
Radio Overview..................................................................................................................2
Software Specifications.....................................................................................................5
Circuit Description.............................................................................................................7
CPU Pins...........................................................................................................................12
TC-780 VHF Parts List 1 (Main Board Unit)....................................................................17
TC-780 UHF Parts List 1 (Main Board Unit)....................................................................38
TC-780 VHF/UHF Parts List 1 (Keyboard Unit) ..............................................................66
Adjustment Description ..................................................................................................67
Troubleshooting Flow Chart ...........................................................................................75
Disassembly and Assembly for Repair..........................................................................79
Exploded View..................................................................................................................83
TC-780 Parts List 2...........................................................................................................84
Packing.............................................................................................................................86
TC-780 VHF PCB View.....................................................................................................87
TC-780 UHF PCB View.....................................................................................................89
TC-780 VHF/UHF PCB View.............................................................................................91
TC-780 Block Diagram.....................................................................................................93
TC-780 VHF Schematic Diagram ....................................................................................94
TC-780 UHF Schematic Diagram..................................................................................101
TC-780 VHF/UHF Schematic Diagram..........................................................................108
Specifications.................................................................................................................110

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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 public-
ation date.
Safety and General Information
The following general safety precautions as would normally apply, should be observed during all phases
of operation, service and repair of this equipment.
This equipment should be serviced by qualified technicians only.
Use only HYT supplied or approved antenna.
Turn off your radio prior to entering any area with a potentially explosive atmosphere.
To avoid electromagnetic interference and/or compatibility conflicts, turn off your radio in any
facility where posted notices instruct you to do so.
When instructed to do so, turn off your radio when on board an aircraft. Any use of a radio must
be in accordance with airline regulations or crew instructions.
To avoid possible interference with blasting operations, turn off your radio when you are near
electrical blasting caps, in a blasting area, or in areas posted: “Turn off two-way radio.”Obey all
signs and instructions.
For vehicles with an air bag, do not place a radio in the area over an air bag or in the air bag
deployment area.
Do not use any portable radio that has a damaged antenna. If a damaged antenna comes into
contact with your skin, a minor burn can result.
Do not expose the radio to direct sunlight over a long time, nor place it close to heating source.
If you wear a radio on your body when transmitting, ensure that the radio and its antenna are at
least 2.5cm away from your body.

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Radio Overview
PTT ( Push -to-
Talk ) Key
SK1 (Side Key 1) SK2 (Side Key 2) Antenna
Microphone Speaker LCD Display Function Keypad
Numeric Keypad TK (Top Key) Channel Selector
Knob
Radio On-Off / Volume
Control Knob
LED Indicator Accessory Jack Battery Latch Belt Clip
Battery Screw, Belt Clip Charging Piece
PTT ( Push–to–Talk ) Key
Press and hold down the PTT key to transmit; release it to receive.

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SK1 (Side Key 1)
Programmable function key.
SK2 (Side Key 2)
Programmable function key.
LCD Display
Used to display radio status information.
Function Keypad
Exit key
Use the Exit key to return to the previous menu.
Up key
Down key
Menu/Select key
Used to enter the menu mode. When you are in the menu mode, this key is also used to make
menu selections.
Numeric Keypad
Used to enter information for programming the radio’s lists.

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TK (Top Key)
Programmable function key.
Channel Selector Knob
Rotate the knob to select a desired channel.
Radio On-Off / Volume Control Knob
Rotate the knob clockwise to turn the radio on, and rotate the knob fully counter-clockwise until a click is
heard to turn the radio off.
Turn the knob clockwise to increase the volume, or counter-clockwise to decrease the volume.
LED Indicator
The following table indicates LED mode and corresponding radio status:
Status LED
Transmit Red
Receive Green
Low battery alert Flash red
After transmitting a call ( within auto reset time ) Orange
After receiving a call ( within auto reset time ) Flash orange slowly
Missed call alert Flash orange rapidly
Scan Flash green
Accessory Jack
The jack is used to connect audio accessories, or other accessories such as programming cable.

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Software Specifications
Specifications
256 Conventional Channels
32 Channel Groups
2-Tone/ DTMF / HDC1200 /HDC2400TM Encode & Decode
ATIS Encode
Priority Channel Scan
When the radio operates in talkaround mode, the channel scan featureprovides users with an easy
way to monitor and join other channels.
a) Revert Channel
Press of the PTT during radio scanning shall cause the radio to transmit on the programmed
revert channel.
b) Nuisance Channel Delete
To ensure accurate scanning, press the Nuisance Channel Delete key to temporarily remove
the nuisance channel from the current scan list.
Busy Channel Lockout
A channel already in use is not available to other users.
Programmable Function Buttons
Six of the radio’s buttons can be programmed as shortcut buttons for your most often used features.
Time-out Timer
The feature allows for more efficient use of channels by limiting the amount of time of each
transmission. The range is from 15 seconds to 600 seconds.
Emergency
Press the Emergency key to emit emergency alarm, or send ENI (Emergency Number Identity) /
background tone to a pre-defined person or the dispatch center, whichever is defined by the
Emergency option. Press the button again to cancel the emergency procedure.
VOX
Dual Home Channels
Optional Functions

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a) Man Down
b) External Scrambler
c) Patrol Record
d) GPS Function
Description
1. User Mode
This mode is for normal operation by end users.
2. All Reset Mode
Allows you to initialize tuning items, channel frequency, and conventional functions. See the
Adjustment Description section for details.
3. Clone Mode
a) Factory Wired Clone Mode
b) Dealer Wired Clone Mode
c) Factory Wireless Clone Mode
d) Dealer Wireless Clone Mode
Press SK1 and to enter clone mode; press SK2 to toggle between wired and wireless clone
modes; press TK to toggle between factory and dealer modes.
4. Manual Adjust Mode
Allows you to adjust frequency deviation, power level, sensitivity, squelch level, and etc.
5. PC Adjust Mode
Allows you to adjust the radio manually or automatically via PC.
Note: You must select Manual Adjust Mode from Optional Features in the Programming
software, before you can enter manual adjust mode. See the Adjustment Descrip-
tion section for details.

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Circuit Description
Circuit Composition
The overall circuit is composed of PLL-VCO circuit, transmit circuit, receive circuit, baseband processing
circuit, power supply circuit, and MCU control circuit.
Frequency Configuration
The receiver section utilizes double conversion. The first IF is 44.85MHz and the second IF is 455 KHz.
The first local oscillator signal is supplied by PLL and VCO circuit. The second local oscillator signal is
generated from TCXO ( 44.395MHz); The PLL and VCO circuit also generates the frequencies required
by the transmit section.
1. Receive Circuit
Configuration of the receive circuit is shown in Figure 1.
Figure 1 Receive Circuit
2. RF AMP BPF
The signal from antenna is amplified at RF amplifier ( Q410 ) after passing through a transmit /
receive switch circuit and a band pass filter. The amplified signal is filtered by a band pass filter
to eliminate unwanted signals before it goes to the first mixer.
3. The First Mixer
The signal output by RF AMP BPF is mixed with the first local oscillator signal output by PLL frequency
synthesizer at the first mixer ( Q415 ) to create a 44.85 MHz first IF signal. The first IF signal is then fed

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through a crystal filter ( XF401) to further remove spurious signals.
4. IF Amplifier
The first IF signal is amplified by Q412 and then enters U403 ( TA31136FN). The signal is mixed with the
second local oscillator signal ( 44.395MHz ) again to create a 455 KHz second IF signal, which passes
through a ceramic filter ( wide band: Z404; narrowband: Z403 ) to eliminate unwanted signals. The
resulting signal is detected by U403 to output audio signal from Pin 9.
5. Audio Amplifier
The Rx audio signal output by U403 is amplified by U201, and then passes through the audio processor
U203 ( the received signalling is separated from the signal for decoding ). The amplified signal then is
fed to AF MUTE, volume switch SW601 ( volume control ) and Q615 ( PA MUTE control ). The resulting
signal is finally fed to the audio amplifier U609 to output audio signal from speaker.
6. Squelch
Noise signal is derived from the Rx audio signal output by Pin 9 of U403, and is processed by U403 to
produce an SQL level. The SQL level is then compared in CPU ( U605 ) to generate a level which
controlsAF MUTE and PAMUTE. It controls Q204 and Q615 to enable or disable the audio path.
Transmit Circuit
The transmit circuit is composed of MIC circuit, frequency synthesizer, driver and final-stage power
amplifier circuit, and the APC circuit.
Figure 2 Transmit Circuit