Kirisun TP620, Руководство по обслуживанию

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TP620 Service Manual
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Rx Circuit RF Part
The high frequency signal from low-pass filter passes the front stage electrically tunable band-pass filter
controlled by electric level and output by DAC (U301 PIN29) so as to filter out the out-of-band interference
signal, sending effective band-pass signal into the low noise amplifier (Q505). The amplified signal passes
again the band-pass filter controlled by electric level and output by DAC so as to filter out the out-of-band
interference signal caused by amplification, sending effective high frequency signal into frequency mixer
(Q506).
The effective signal passes RF band-pass filter and low noise amplification and enters the frequency
mixer Q506, meanwhile, the first local oscillation generated by VCO passes the low-pass filter and enters
Q506 for making frequency difference with effective signal so as to generate the first IF signal. The signal
passes the frequency selector network which consists of LC; it further suppresses the other carrier waves
other than the first IF, and increases the isolation between the frequency mixer and IF filter. The IF signal
will be filtered by the XF501 crystal filter, and then sent to the first IF amplifier (Q507) for amplification
before being sent to the IC for IF processing (U501, GT3136).
The third harmonic frequency 50.4MHz produced by TCXO(X601 16.8MHz) is amplified by frequency
selector and become the second local oscillation signal source. The second local oscillation (50.4MHz)
mixes with the first IF signal in U501, generating the second IF (450kHz). The second IF will be amplified,
limiting amplitude inside U501, and filtered by the ceramic filter CF501 450kHz before going back to U501
for demodulating and outputting the audio signal.
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Rx Circuit Audio Section
A. Digital Channel Audio Access: The second IF signal output from the eleventh pin of U501 is amplified
by Q509 and sent to U201 for ADC sampling and being converted to digital signal; after the digital audio
signal is compressed, decompressed and decoded by U301, U201 will complete DA conversion and
output audio signal from the 10th pin, and the audio signal will be amplified by U203 and sent to the
audio power amplifier IC101.
B. Analog Channel Audio Access: The audio signal output from the 9th pin of U501 is amplified by U102
and its unit circuit. The high frequency and low frequency will be removed from the audio signal,
keeping only the voice component between 300 Hz to3000Hz. The voice component will be adjusted by
volume potentiometer and sent to audio power amplifier IC101.
C. Analog Channel CTCSS/DCS Signaling Access: The audio signal output from the 9th pin of U501
may include CTCSS/DCS signal. The 300Hz low-pass filter circuit composed of U101 filters out the
signals out of the CTCSS/DCS spectrum. After CTCSS/DCS is amplified, it will be sent to the 25th pin of
U301.
D. Analog Channel Squelch Circuit: The modulated output from U501 is sent to the frequency selector
noise amplifier which is composed of U501 internal noise amplifier and C555, R525, R524, C554, C553,
R527; the noise will be selected from the modulation signal and detected internally before being
outputting by the 14th pin and transformed as direct electric level to reach MCU U301; MCU identifies
the electric level strength and controls squelch.
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