Kirisun PT6500, Service Manual

4

comparator, and the upper limiting filter.

Q6, D2, D4, D5 and D6 constitute the transmitting VCO unit. D9 is 

the modulating circuit of the transmitting VCO.

Q11, D11, D12, D13 and D14 etc. constitute the receiving VCO 

unit.

IC2 (ADF4111) is the PLL integrated circuit, which can comprise 

the programmable reference frequency divider, programmable 

frequency divider, phase comparator and charge pump, etc.

The upper limiting filter consists of R43 and C96 etc.

The frequency reference is provided by X1 (TCXO, 12.8MHz).

The frequency reference from TCXO (temperature control crystal 

oscillator) receives frequency division by the programmable 

reference frequency divider in IC2 to generate the frequency 

reference of 5kHz or 6.25kHz (according to the frequency of the 

channel, controlled by MCU).

The oscillation frequency from VCO is sent to IC2, after frequency 

division by the programmable frequency divider, it is compared 

with the frequency reference to get the error signal, which is, after 

wave filtering by the upper limiting filter, sent to VCO to change 

the oscillation frequency of VCO, which allows the VCO frequency 

to achieve the set value and the VCO to be locked.Detection of 

loss of lock: if PLL loses lock, IC2 pin14 outputs low level signal to 

MCU, which prevents the transmitter from transmitting and 

generates alert.

Q13 and related circuits are used for switching the upper limiting 

filter.

3.5 Audio Processing Circuit:

I

C6 (AK2346) is a special voice processing chip provided with 

functions like amplification, wave filtering, preemphasis, 

deemphasis, scrambling, companding and MSK MODEM etc. Most 

voice processing tasks of the radio are completed by it.

MIC Signal Processing:

Voice signals from MIC are controlled by AGC circuit, and then 

reach IC24, one group of signals are amplified at IC24B (VOX 

circuit) and are processed into direct current by D35 and sent to 

MCU for processing; the other group of circuits are amplified at 

IC24A and then receive amplification, wave filtering, companding 

(optional), preemphasis, scrambling and amplitude limit at IC6 pin3, 

after that, they are exported from IC6 pin7 and sent along with 

CTCSS/DCS to VCO for modulation.

2T/5T signals are imported from IC6 pin6, and after amplitude limit 

and amplification, they are exported form IC6 pin7 and sent to VCO 

for modulation.

Receiver Audio Signal Processing:

Voice signals exported from IC4 are divided into two channels, one 

comes to the low pass circuit (voice signals filtered) consisting of 

IC5, etc for amplification and wave filtering to get comparatively 

pure CTCSS/DCS signals, which are then sent to MCU for 

processing; the other comes to IC6 pin23, after amplification and 

wave filtering, one channel is exported from IC6 pin21 (DTMF/2T/5T 

signals etc.), DTMF/2T/5T signals etc. come through the high pass 

circuit (sub-audio signals filtered) consisting of Q30 and Q31 etc., 

DTMF signals come to IC10 (special chip for HT9172 DTMF 

decoding) for decoding and then sent to MCU for processing, 2T/5T 

signals are sent to MCU for processing after wave filtering and 

waveform modification by IC1; the other channel of signals (voice 

signals) are exported form IC6 pin18 after scrambling, preemphasis, 

deemphasis and companding and then imported from IC6 pin19 for 

amortizing and amplification before being exported form IC6 pin20.

IC13 is a voice storage chip, which stores voices including channel 

prompt etc., each time the channel is changed, the speaker will 

prompt the current channel number by voice. Press the 

voice 

prompt

 key to prompt the current channel number again. 

Receiver audio signals, voice prompt signals, 2T/5T/DTMF signals, 

prompt voice signals, emergent alert signals are gathered to be 

amplified by the audio frequency amplifier IC9 to drive the speaker.

Speaker impedance: 16Ù.

Note: None of the terminals of the speaker can be grounded!

The volume of emergent alerts cannot be controlled.

3.6 Power Supply:

The radio is equipped with 7.4V battery as power supply, which 

directly supply power to transmitter power amplifier circuits (Q1, Q3) 

and receiver audio power amplifier (IC9), other circuits adopts 

regulated 5V power supply.

Q40, Q45: 5V low voltage difference, micro power regulator.

      Q43: 5T switch, controlled by MCU.

      5T: Supplies power for the front terminal of the transmitter.

      Q39: 5R switch, controlled by MCU.

     5R: Supplies power for the receiver RF amplification, mixing, IF 

processing, audio signal processing..

      Q44: 5C switch, controlled by MCU.

     5C: Th e 5V power controlled by power saving supplies power for 

the frequency synthesizer.

3.7 MCU:

  MCU controls the working of each unit of the radio to realize 

all the radio functions.

        Connects with the PC

         Accesses the current channel status data 

 Controls the PLL to generate receiver and transmitting local 

oscillation frequency

  Acquires current channel status 

 Controls the LED status indication 

Controls the power supply of each location 

Checks the action of each function key 

Generates CTCSS signals 

Generates DCS signals 

Generates power control signals

CTCSS decoding

DCS decoding 

Squelch check and control 

Controls the content of voice indication 

Memorizes the radio channel data, CTCSS/DCS data, and other 

data of function setting and parameter adjustment.

CTCSS/DCS Encoding and Decoding:

2

Memorier (E PROM, AT24C256)

PT6500 SERVICE MANUAL

1

1

2

2

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4

4

D

D

C

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B

B

A

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Titl e

Number

Revision

Size

A4

Date:

2007-7-26

Sheet    of

Fil e:

X:\ PT6500\..\ AUDI O.SchDoc

Drawn By:

pin 7

Q30

HP

Q31

HP

IC1A

HP

AMP

IC1B

IC10

HT9172

IC5A

IC5B

IC5C

IC5D

AMP

LP

LP

AMP

CTCSS/ DCS

DTMF

2T

AK2346

IC6

IC4 pi n 9

AF AMP

IC9 TDA 8541

pin 20

MIC AMP

MCU

IC7

pin 23

pi

n

6

pi

n

3

MIC

SP

Figure 3.5 Audio Processing Diagram