QUANTUN QP-750 User manual

QP-750 Service Manual
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QP-750 Service Manual
Quantun Electronics，
，，
，LLC

QP-750 Service Manual
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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 precautions are 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 a qualified technician only.

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Table of Contents
Chapter 1 Test Equipment, Service Aids, and Service Tool......6
1.1 Test Equipment………………………………………………………................................6
1.2 Service Aids……………………………………………………………………...................6
1.3 Model…………………………………………………………………………………………7
Chapter 2 Realignment………………………………………………8
2.1 Getting acquainted…………………………………………………………………………8
2.2 Radio modes………………………………………………………………………………..9
2.2.1 User Mode………………………………………………………………………………………...9
2.2.2 All Reset Mode……………………………………………………………………………………9
2.2.3 Wireless Clone Mode…………………………………………………………………………….9
2.2.4 User Wired Clone Mode………………………………………………………………………….9
2.2.5 Manual Adjust Mode…………………………………………………………………………….10
2.2.6 PC Adjust Mode………………………………………………………………………………….11
2.3 Adjustment Description…………………………………………………………………….11
2.3.1 Required Test Instrument………………………………………………………………………..11
2.3.2Adjustment………………………………………………………………………………………...…11
Chapter 3 Disassembly and Assembly………………………..….14
3.1 Disassemble the radio…………………………………………………………………….14
3.1.1 Remove the battery………………………………………………………………………………14
3.1.2 Remove the antenna…………………………………………………………………………….14
3.1.3 Remove the knob…………………………………………………………………………………15
3.1.4 Separate the chassis from PCB………………………………………………………………...15
3.1.5 Remove the main PCB……………………………………………………………………….....15
3.1.6 Disassemble PTT key……………………………………………………………………………16
3.2 Assemble the radio…………………………………………………………………………17
3.2.1 Attach PTT …………………………………………………………………………………… 17
3.2.2 Assemble the chassis and PCB…………………………………………………………………17
3.2.3 Attach the battery…………………………………………………………………………………17
Chapter 4 Mechanical View and Parts List………………………19
4.1 Exploded view………………………………………………………………………………19
4.1 QP-750 Part List……………………………………………………………………………20
Chapter 5 DC Power Distribution……………………...................21
5.1 DC Regulation and Distribution……………………………………….….......................21

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Chapter 6 Controller Theory of Operation………………………23
6.1 Controller…………………………………………………………………………………..23
6.2 Microprocessor Circuitry………………………………………………………………….23
6.2.1 Memory Usage…………………………………………………………………………………..24
6.2.2 Control and Indicator Interface……………………………………………....…………………24
6.2.3 Interface to RSS Programming…………………………………………………………………24
6.2.4 Storage of Customer-Specific Information…………………………………….......................24
6.2.5 Sensing of Externally-Connected Accessories……………………………...........................24
6.2.6 Microprocessor Power-Up, Power-Down and Reset Routine…………………...................25
6.2.7 CPU PINs………………………………………………………………………………………….25
6.3 Audio Circuitry………………………………………………………………………………28
6.3.1. Transmit and Receive Low-Level Audio Circuitry………………………………………………28
6.3.2 Audio Power Amplifier……………………………………………………….............................28
6.3.3 Internal Microphone Audio Voice Path…………………………………………………………29
6.3.4 PTT Circuits…………………………………………………………………..............................29
6.3.5 VOX Operation……………………………………………………………….............................29
6.3.6 Programming and Flashing through Microphone Jack……………………………………….29
Chapter 7 UHF Theory of Operation………………….………….30
7.1 Introduction……………………………………………………………………………….. 30
7.2 UHF Receiver……………………………………………………………………………. 30
7.2.1 Receiver Front-End……………………………………………………………………………30
7.2.2 Receiver Back-End…………………………………………………………………………….30
7.2.3 Narrowband/Wideband Switch Circuit……………………………………………………….31
7.3 UHF Transmitter ……………………………………………………………………………………..31
7.3.1 AF and Signaling……………………………………………………………………………….32
7.3.2 RF Power Amplifier…………………………………………………………………………….32
7.3.3 Antenna Switch and Harmonic Filter………………………………....................................32
7.3.4 APC……………………………………………………………………………………………...32
7.4 PLL Frequency Synthesizer ……………………………………………....................................32
7.4.1 PLL Circuit……………………………………………………………………………………..33
7.4.2 VCO…………………………………………………………………….................................33
7.4.3 Unlock Detector……………………………………………………………………………….33
7.5 Base Band and Signaling System… …………………………………………………………...34
7.5.1 CTC/CDC………………………………………………………………………………………34
7.5.2 DTMF / 2-Tone………………………………………………………………………………..34
7.5.3 MSK…………………………………………………………………………………………….35
7.5.4 AF………………………………………………………………………………………………35
Chapter 8 UHF Troubleshooting Tables………………………….36
8.1 Troubleshooting for CPU……………………………………………………… ………….36
8.2 Troubleshooting for VCO………………………………………………………… ……….37
8.3 Troubleshooting for Receive…………………………………………………………….38
8.4 Troubleshooting for Transmission………………………………………………………39

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Chapter 9 UHF Schematic Diagrams, Layout, Parts Lists…….40
9.1 Introduction…………………………………………………………………………… …40
9.2 QP-750 block diagrams……………………………………………………………… …41
9.3 QP-750 UHF Schematic Diagrams…………………………….……………………... 42
9.3.1 QP-750 RF Section…………………………………………………………………………42
9.3.2 QP-750 VCO Section……………………………………………………………………….43
9.3.3 QP-750 PLL Section…………………………………………………………….…………..44
9.3.4 QP-750 Base Band Section…………………………………………….………………….45
9.3.5 QP-750 AF Section……………………………………………………….………………..46
9.3.6 QP-750 Controller Section…………………………………………….………………… 47
9.4 QP-750 UHF PCB Layout………………………………………………..…………… 48
9.4.1 QP-750 UHF PCB Top layer view ………………………………………….…………… 48
9.4.2 QP-750 UHF PCB Top Chip Map………………………………………….………….…..49
9.4.3 QP-750 UHF PCB Bottom layer View……………………………………....………….…50
9.4.4 QP-750 UHF PCB Bottom Chip Map……………………………………………………...51
9.5 QP-750 (450-470MHz) Parts List…………………………………………………..…53
Chapter 10 Specification……………………………………….…78

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Chapter 1 Test Equipment, Service Aids, and
Service Tools
1.1 Test Equipment
Table 1-1 lists test equipment required to service the QP-750 Radios.
Table 1-1. Recommended Test Equipment
Description
Char
acteristics
Application
Communication Test
Set
Frequency/deviation meter and signal
generator for wide-range troubleshooting and
RF level measurements and receiver
sensitivity measurements
Digital multimeter
True RMS metering,
Digital voltmeter is recommended
for AC/DC voltage and current measurements
Dual channel
100 MHz oscilloscope
Two-channel, 100 MHz
bandwidth, 200 M sample
rate/sec, 2 MB memory/
channel
Waveform measurements
1.2 Service Aids
Table 1-2 lists service aids recommended for working on the QP-750 Radios. While all of these
items are available from Quantun, most are standard shop equipment items, and any equivalent
item capable of the same performance may be substituted for the item listed.
Table 1-2. Service Aids
Description
Applica
tion
DC Power Supply Regulates DC voltage between radio and power supply.
Customer Programming Software
Program customer option and channel data.
Test Cable Connects radio to test equipment.
RF Adaptor Adapts radio’s antenna port to BNC cabling of test equipment.
Battery Adaptor Interconnects radio to power supply.
Knob Remover/Chassis Opener Used to remove the chassis form front cover assembly, knobs
from the switches.
Programming Cable
Connects the computer’s serial communications adapt to radio
and enables communications between the radio and the
computer.
Radio-to-Radio Cloning Cable
Allows a radio to be duplicated from a master radio by
transferring programmed data from the master radio to the
other.

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Table 1-3. Recommended Service Tools
Des
cription
Application
screwdriver Tighten and remove chassis screws
Digital readout solder station Digitally controlled soldering iron
Hot air workstation, Tool for hot air soldering/desoldering of surface
mounted integrated circuits
Illuminated magnifying glass with
lens attachment Illumination and magnification of components
Anti-static grounding kit Used during all radio assembly and disassembly procedures
Brush
Solder, 0.5mm diameter
1.3 MODEL LIST
QP750, UHF, 450-470 MHz
Model
Description
QP750 (XMHQP
-
750U)
QP750
,
450
-
470
MHz, 5W, 16
CH
Accessories
QSBP0M080010
QS4501000000
QSAN0W410000
QC750100020
Li-Po battery 2100 mAh
Belt clip
Antenna Whip 450-470 MHz
Programming cable kit with USB conector
QC750200010 Programming cable kit with serial port
QSCHOM080010
SC1002 QP
-
750 Intelligent Ch
arger
–
Base
only
QBM102PCB Earphone with microphone/PTT

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Chapter 2 Realignment
2.1 Getting acquainted
1. Antenna
2. Channel Selector knob
3. LED indicator
4. Power/Volume Control Knob
5. External Jack
6. PTT Key
7. SFK2 （ Programmable Key ）
8. SFK1 （ Programmable Key ）
9. TFK （ Programmable Key ）

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2.2 Radio modes
2.2.1 User Mode
This mode is for normal operation.
2.2.2 All Reset Mode
Firstly ground the SELF point, and then turn the power on while holding down TFK key for 2 seconds.
The radio enters all reset mode with green LED flashing twice. Turn the channel selector knob to the
selected channel and press PTT, the green LED lights, then switch off the radio. The radio data is all
reset (All clone modes will be automatically activated when All Reset is completed). Frequency
settings are shown as follows:
Selected
Channel
Frequency
Band
(MHz)
F1 (MHz) F2 (MHz) F3 (MHz) F4 (MHz) F5 (MHz)
1 136
～ 174 TX1:136
RX1:136.1
TX2:145.5
RX2:145.6
TX3:155
RX3:155.1
TX4:164.5
RX4:164.6
TX5:174
RX5:173.9
8 450
～ 520 TX1:450
RX1:450.1
TX2:467.5
RX2:467.6
TX3:485
RX3:485.1
TX4:502.5
RX4:502.6
TX5:520
RX5:519.9
9 400
～ 470 TX1:400
RX1:400.1
TX2:417.5
RX2:417.6
TX3:435
RX3:435.1
TX4:452.5
RX4:452.6
TX5:470
RX5:469.9
2.2.3 Wireless Clone Mode
Select wireless clone from Optional Features in programming software, turn the power on while
holding down PTT and SFK2 key simultaneously for 2 seconds, then the source and target radios
enter wireless clone mode with red LED flashing twice （ After the source and target radios are turned
on and stay in the same channel, hold down PTT on the source radio to begin cloning ） . During
cloning, the LED of the source radio glows red and that of the target radio glows green. The target
radio flashes green and two Beeps are heard in case of successful cloning, it flashes red in case of
cloning failure.
2.2.4 User Wired Clone Mode
Select Wired Clone from Optional Feature in programming software, turn the source radio power on
while holding down PTT and SFK1 key simultaneously for 2 seconds, then the source radio enters
user wired clone mode with red LED flashing one time. Then directly turn the target radio on. Press
PTT on the source radio to begin cloning. During cloning, the LED of the source radio glows red and
that of the target radio glows green. The LED of the source radio goes out in case of successful
cloning, it flashes red in case of cloning failure.

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2.2.5 Manual Adjust Mode
Manual adjustment is performed to adjust frequency deviation, power, sensitivity, squelch, etc.
Note: Prior to entry for mode startup, select Manual Adjust Mode from optional functions in
programming software. Manual Adjust Mode Description is as following:
(1) Enter the manual adjust mode
Turn the power on while holding down PTT and TFK key simultaneously for 2 seconds, then the
radio enters manual adjust mode with orange LED flashing twice.
(2) Channel number on the channel selector knob
Each channel number is for a setting adjustment item. when changing a channel by rotating the
Channel Selector Knob, the channel is defined as 25KHz bandwidth and low frequency (F1).
(3) SFK2 key
Used to set the frequency. 1 point tuning adjusts center frequency; 3 point tuning adjusts F1, F3, F5;
5 point tuning adjusts F1-F5.
The frequency toggles from low frequency to high frequency. Green LED flashes one time when F1
is selected.
(4) TFK key
Use to toggle the channel bandwidth between 25 KHz, 20 KHz and 12.5 KHz. Red LED flashes one
time when the bandwidth is 25 KHz.
(5) PTT/SFK1
PTT →Decrease
SFK1→Increase
PTT/SFK1 is pressed to adjust downward/upward. Red LED glows indicating the maximum adjust
value and green LED indicating the minimum value. Hold down the key to increase/decrease the
adjustment value continuously.
Press PTT key to save the BATT LOW, SQL and VOX settings, then green LED glows once.
(6) Select adjustment item group:
The first group of adjustment items is selected when the radio enters the manual adjust mode.
Turn to CH16 and press PTT key to enter the next group. Press it again to return to the first group.
Orange LED flashes once when the first group of adjustment items is selected and flashes twice
when the second group is selected.

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(7) Frequency Setting
5 point tuning （ MHz ） TX: { TX1,TX2,TX3,TX4,TX5}
RX: { RX1,RX2,RX3,RX4,RX5}
3 point tuning （ MHz ） TX: { TX1, TX3, TX5}
RX: { RX1, RX3, RX5}
1 point tuning （ MHz ） TX: { TX3}
RX: { RX3}
2.2.6 PC Adjust Mode
Select test mode from programming items in programming software and then begin adjustment.
2.3 Adjustment Description
Adjust the radio by PC programming software or by manual adjustment. In manual adjustment mode,
the adjustment method is shown as follows: (Refer to “Modes” for the manual adjustment mode)
2.3.1 Required Test Instrument
Radio Communication Test Set 1 set
3A/10V Power Supply 1 set
Digital Voltmeter 1 set
3A Ammeter 1 set

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2.3.2 Adjustment
Firstly reset the radio. Refer to All Reset Mode in ”Modes” for more details:
VCO adjustment
(1) Adjustment in user mode
(2)Setting Power supply voltage: 7.4V
Item Condition Measurement Adjustment Specification
Test
Instrument
Terminal Parts Method
1.
2.Transmit
VCO lock
voltage
1. CH: TX high Digital
Voltmeter
CV TC1350
TC1351
4.2V ± 0.3V
2. TX Low Check >0.7V
3.Receive
VCO lock
voltage
1. CH: RX high 4.2V
± 0.3V
2. RX low Check >0.7V
Transmitter adjustment
(1) Enter the manual adjust mode
(2) Setting Power supply voltage: 7.4V
Item
Condition
Test
Instrument
Method
Purpose
Group 1
0. Transmit
frequency
Turn to CH1; Radio
Communicat
ion Test Set;
TX Test
Adjust VR21 Frequency Error
≤ 100Hz
1. TX power
Low
Turn to CH1.
Adjust at 5 point (wideband).
Radio
Communicat
ion Test Set
TX TEST
HPF ： 20HZ
LPF ： 300HZ
PTT key
SFK2 key 1.1W±0.2W
2. CDCSS
balance
Turn to CH2.
Adjust at 3 point (wideband),
PTT key
SFK2 key
standard waveform
3. CDCSS
deviation
Turn to CH3.
Adjust at 3 point (wideband),
1 point (medium band)
1 point (narrowband)
PTT key
SFK2 key
750Hz (25KHz),
600Hz (20KHz)
400Hz (12.5KHz)
4. CTCSS
(67.0Hz)
deviation Low
Turn to CH4.
Adjust at 3 point (wideband),
1 point (medium band)
1 point (narrowband).
PTT key
SFK2 key
5. CTCSS
(136.5Hz)
deviation
Center
Turn to CH5.
Adjust at 3 point (wideband),
1 point (medium band)
1 point (narrowband)
PTT key
SFK2 key
6. CTCSS
(254.1Hz)
deviation High
Turn to CH6.
Adjust at 3 point (wideband),
1 point (medium band)
1 point (narrowband).
PTT key
SFK2 key

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7. AK2346
Transmit Audio
Deviation
Turn to CH7.
Adjust at 3 point(wideband),
1 point (medium band),
1 point (narrow band).
Radio
Communicat
ion Test Set
HPF: 20Hz
LPF: 15KHz
1KHz
120mV
PTT key
SFK2 key 4KHz (25KHz),
3.2KHz (20KHz)
2KHz (12.5KHz d)
8. 2 Tone
deviation
Turn to CH8.
Adjust at 1 point (wideband),
1 point (medium band),
1 point (narrow band).
Radio
Communicat
ion Test Set
TX Test
HPF: 20Hz
LPF: 15KHz
No
modulation
signal.
PTT key
SFK2 key
3.2KHz (25KHz),
2.5KHz (20KHz)
1.8KHz (12.5KHz)
9. DTMF
deviation
Turn to CH9.
Adjust at 1 point (wideband),
1 point (medium band),
1 point (narrow band).
PTT key
SFK2 key
3.2KHz (25KHz)
2.5KHz (20KHz)
1.8KHz (12.5KHz),)
10. MSK
deviation
Turn to CH10.
Adjust at 3 point (wideband),
1 point (medium band),
1
point (narrow band).
PTT key
SFK2 key
3.2KHz (25KHz),
2.5KHz (20KHz)
1.8KHz (12.5KHz).
11. VOX
GAIN1
Turn to CH11.
Adjust at 1 point (wideband).
Radio
Communicat
ion Test Set
TX TEST
HPF: 20HZ
LPF: 15KHZ
Save Modulation signal:
1KHz, 45mv
Press
PTT to save;
12. VOX
GAIN5
Turn to CH12.
Adjust at 1 point (wideband).
Save Modulation signal:
1KHz, 15mv
Press PTT to save;
13. TX power
HIGH
Turn to CH13.
Adjust at 5 point (wideband). Radio
Communicat
ion Test Set
TX TEST
PTT key
SFK2 key
5W±0.3W
14. TX voltage
Low
Turn to CH14.
Adjust at 1 point (wideband).
Save Adjust voltage to
6.0V,press PTT to
save
Receiver Adjustment
(1) Enter the group 2
(2) Setting the power supply voltage: 7.4V
Item Condition Test Instrument Method
Purpose
Group
2
1. RX sensitivity Turn to CH1.
Adjust at 5 point (25KHz).
Radio
Communication
Test Set
RX TEST
HPF ： 300HZ
PTT key
SFK2
key
Adjust level to
120dBm.
SINAD≥12dB
2. AK2346 RX
volume
Turn to CH2.
Adjust at 1 point (25KHz),
1 point (20KHz)
1 point (12.5KHz)
PTT key
SFK2 key
When Max. volume is
set, adjust AC level
to 1.5W (16 Ω ),
single output
2.
3
±
0.3
V,
3. Squelch Level 3
(OPEN)
Turn to CH3.
Adjust at 5 point (25KHz),
1 point (20KHz)
1 point (12.5KHz)
Save Adjust level to
-123dBm ， press PTT
to save
4. Squelch Level 3
(SQUELCH)
Turn to CH4.
Adjust at 5 point (25KHz),
1 point (20KHz)
1 point (
12.5KHz
)
.
Save Adjust level to
-125dBm ， press PTT
to save

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5. Squelch Level 9
(OPEN)
Turn to CH5.
Adjust at 5 point (25KHz),
1 point (20KHz)
1 point (
12.5KHz
)
LPF ： 3KHZ
Save Adjust level to
-117dBm ， press PTT
to save
6. Squelch Level 9
(SQUELCH)
Turn to CH6.
Adjust at 5 point (25KHz),
1 point (20KHz)
1 point (12.5KHz)
Save Adjust level to
-119dBm ， press PTT
to save
7. RX voltage Low Turn to CH7.
Adjust at 1 point (25KHz).
Save Adjust power supply
voltage to 6.3V, press
PTT to save
Note: AF deviation of the receiver is 3KHz (wideband) ， 2.5KHz(medium band) and 1.5KHz (narrowband)

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Chapter 3 Disassembly and Assembly
3.1 Disassemble the radio
3.1.1 Remove the battery
(1) Turn off the radio if it is turned on.
(2) Disengage by pushing downward and holding the latch towards the front of the radio.
(3) With the battery latch disengaged, slide the battery down from the top of the radio about 12mm.
Once the battery is free from the battery rails, lift it directly away from the radio.
3.1.2 Remove the antenna.
Remove

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3.1.3 Remove the knob.
3.1.4 Separate the chassis from PCB
(1) Insert a open tool into the clearance between chassis and the case.
(2) Push the tool downwards to separate the chassis from the case.
(3) Lift the bottom of the chassis and pull it out of the PCB.
3.1.5 Remove the main PCB
(1) Remove the two nuts on top of the unit for the channel coder and power switch.
(2) Remove the ten screws between PCB and the chassis.
(3) Loosen the weld between antenna pedestal and PCB using a soldering iron.
(4) Lift the PCB off.

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3.1.6 Disassemble PTT key
Push the tab on PTT out of the hole on the case to disassemble PTT key.

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3.2 Assemble the radio
3.2.1 Attach PTT
（ 1 ） First insert the silica rubber PTT key form the inner of the radio house.
（ 2 ） Then press the down end of the PTT cover into the slot on the front case.
（ 3 ） Finally align the tab on PTT with the corresponding hole on the case.
3.2.2 Assemble the chassis and PCB
（ 1 ） Insert the switch shaft in front of the PCB into the corresponding holes on the case.
（ 2 ） Press the bottom of the chassis downwards until a click is heard.
（ 3 ） Make sure the water-proof packing attached to the circumference of the chassis is securely
inserted in the groove of the chassis

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3.2.3 Attach the battery:
（ 1 ） Align the battery to the battery rail on the back of the radio (approximately 12mm from the top
of the radio.)
（ 2 ） Press the battery firmly to the radio and slide the battery upward until the latch snaps into
place.

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Chapter 4 Mechanical View and Parts List
4.1 Exploded view
12345 7 9
11
B
68
A B
1
2
3
5
10
12
13
14
15
16
17
18
19
20
21
24
22
26 27 28 29 25
23
34 35 36
31 32 33
30
A
A
A
AA
A
A