BBK AV215T User manual

Principle, Knowledge and Maintenance of
AV215T (RU)
Contents
Chapter One Product Description
Chapter Two Operating Principle
Section One Overall Structure
Section Two Volume Board
Section Three Signal Processing Board
Section Four CPU Board
Section Five Control Panel
Section Six Power Panel
Section Seven Power Amplifier Board and Protection Circuit
ChapterThree MaintenanceProcess

Chapter One Product Description
AV215T (RU) is an advanced power amplifier with complete functions that adds
LCD to its predecessor as well as 16 kinds of spectrum displays in the sky-blue
background which makes it more extraordinary. The radio reception makes this type
of device the best choice for users who are fond of radios. Its main features are as
follows:
1. Built-in 5-track power amplifier that can adapt toAC-3/DTS and stereo music
playback. It is powerful with 80W main channel and 15W centre surround sound.
2. Mixing input interface of AC-3/DTS, VCD and DVD and DBB and stereo output
interface.
3. 6-channel volume control and independent level control as well as 7-band EQ.
4. Bass Enhancer system, cyber logic and Hi-Fi playback.
5. One button for movie, music and karaoke.
6. Multiple EQ modes that adapt to different music styles.
7. Automatic spectrum analysis and compensation, automatic signal compensation.
8. Multiple spectrum display modes.
9. Complete karaoke function including microphone independent volume control,
overall volume control, pitch adjustment, voice compensation, delay and echo
adjustment as well as the newly added earphone output.
10. Karaoke wide sound field function.
11. Tuning function.
12. Intelligent protection of over-current and over-voltage.
Chapter Two Operating Principle
Section One Overall Structure
AV215T (RU) mainly consists of the following seven parts:
I. Volume Board: Select input signal source, cyber logic and bass enhancer.
II. Signal Processing Board: Karaoke signal processing and 5.1CH signal
amplification.
III. CPU Board: Overall control, frequency point gating, automatic circuit search.
IV. Control Panel: LCD display, remote control keyboard and backlight display.
V. Power Panel and Protection Circuit: Provide operating voltage required by unit
circuits and overall protection.
VI. Power Amplifier Board: Power amplification of 5.1CH signal or analog signal.
VII. Tuner: Receive radio signal and send to amplifier for signal-processing.
Section Two Volume Board
AV215T (RU) has four input modes: Radio input, VCD, DVD and 5.1CH.
The cyber logic function of AV215T (RU) is to get C/SR/SL/SW track signals by sampling
from L/R track and then processing through low-pass filter and adder subtractor. Mode

switch is achieved by using electronic analog switch. The signal flow chart is as follows:
I.
Input selection and sound field processing mode
The input selection of AV215T (RU) is achieved via electronic switches CD4052
and CD4053, the truth tables of which are as follows:
CD4052 Truth Table CD4053 Truth Table
Tuner VCD DVD 5.1 A X B Y C Z
A 0 0 1 1 0 X0 0 Y0 0 Z0
B 0 1 0 1 1 X1 1 Y1 1 Z1
5.1CH input mode: Now A/B/5.1CH control pins of M62446 are of high level. L/R
N
108B
S-C CD
4053
Electro
nic
switch
N
103
S-SL
S-SR
Tuner
CD405
2
Electronic
switch
N101
5.1CH
VCD
DVD
N106
M62446
R
L
CD
4053
Electro
nic
switch
N
104A
N
104B
N
107B
N
105B
N
105A
N
107A
SR
S-C
C
SL
SWIN
SW
DISPLY
OUT

track signal of 5.1 input is outputted from pin 3/13 of N101 and sent to IC N106 for
volume and tone adjustment; meanwhile, C/SR/SL signal on 5.1 input terminal is
respectively sent from pin 14/15/4 output of N410 to IC N106 for independent
volume adjustment. And SW signal is outputted via pin 4 of N103 and then send to
M62446 after being amplified by N107A.
Three analog input modes: AV215T (RU) totally has three analog input modes:
Tuner receiving signal/VCD/DVD, which are controlled via A/B signal respectively
(see details in truth tables).
AV215T (RU) totally has three sound field modes: standard sound field, cyber logic
and Hi-Fi.
1. Standard sound field: Under overall CPU control, when bass enhancer is off, L/R
channel and subwoofer output are available; when bass enhancer is on, only L/R
channel output is available.
2. Hi-fi: Under overall CPU control, only L/R tracks output is available to M62446;
3. Cyber logic:
Pin 9/10 of electronic switch N101 (CD4052) select a series of analog L/R track
input signals according to the truth table. L/R signals are outputted from pin 13/3
via the internal electronic switch of N101, and divided into two ways. One way is
respectively sent into pin 13/15 of M62446, for electronic volume and tone control.
The other way produces SW/S-SR/S-SL/S-C signals via buffer, adder-subtractor
and low-pass filter. SW/S-SR/S-SL signals are sent to pin 12/2/5 of N102. N102
select cyber logic signal input (see truth table of CD4053) from cyber logic and
5.1CH signals, outputs C/SR/SL signals and sends into pin 11/8/9 of M62446 for
volume control. Still another way of SW signal directly sends to pin 6 of M62446
after being outputted from N107A. 5.1CH signal sent into M62446 is outputted
from pin 31-36 after volume and tone control, and then outputted to signal board
by XS20 power distributor.
The relation between sound sources in input circuit and sound processing modes is as
illustrated below.
II. Control circuit
Pin 23/26/27 of CPU (N100) output data, PVST and clock signal and send to pin
39/40/41 of M62446 to control pin 1/2/3/4 of M62446 to output control level, so as to
select input signal and spectrum sampling signal. It is worth noting that PVST signal
is a latch control signal. When data and clock of CPU are sent to M62446, an
identification signal will be added, indicating that this signal can only be used by
M62446 while other IC of I2C bus cannot use current data and clock signal.

III. Frequency spectrum sampling circuit
Only S-C/S-SR/S-SL/SW signals are sampled during frequency spectrum sampling in
AV215T（RU）and added to pin 14 via a 150K sampling resistance. Another S-C cyber logic
signal is added to pin 1 of N103, called S-C. 5.1CH and LR-T of M62446 select sampling
signals. When cyber logic is selected, the control signal of 5.1CH is of low level while pin
9/11 of N103 is of low level. According to the truth table, it is known that the outputs are
X0/Z0. Sampling signal is grounded while LR-T is of H level. Select Y1, S-C＇signal is
outputted from pin 15 of N103 to N108B, adding to OK-R signal for the amplification of
frequency spectrum signal, and then sent to frequency point gating and auto search circuits.
.ⅣTuning function
This device has the tuning function which provides users a good functional option. It
directly controls radio-head and receives audio frequency signal mainly via CPU and then
outputs after amplified via power amplifier. The clock and data line of radio-head are
shared with LM62446 and the other two control lines are connected to CPU directly. L, R
signal processed by radio-head can be sent to N101 IC CD4052 directly to input the
selected track.
Section Three Signal Processing Board
The signal processing board superposes, mixes and amplifies 5.1CH signal sent from the
volume board, voice signals from the voice board and karaoke signal.
I. AV215T（RU）Karaoke Circuit
1. Function: this circuit processes human voice through power amplifier and
reproduces it via speaker. It includes human voice beautification circuit, wide sound field
processing circuit, karaoke echo and delay adjusting circuit.
Press INPUT
b
utton to
circularly
select
Two analog
input modes
5.1 inpu
t
mode
Hi-fi
mode
Standard
sound
fi
e
l
d
Cyber
logic
L/R channel output only. Soun
d
filed and EQ setup not available.
L/R/SW output only. Concer
t
hall sound filed and EQ setup
available
6CH output. Theater sound file
d
and EQ setup available
6CH output. Theater sound file
d
and E
Q
setu
p
available

IC and its functions for karaoke
IC serial
number Name of IC Functions
N201 4558 Transmittal. Preamplification for karaoke signal
N200 PT2315 Volume control of karaoke, including tone control
N205 CD4053 Electronic switch
N209 PT2399 Karaoke echo processing
N207 CD4051 Karaoke delay adjustment
N208 CD4051 Karaoke echo control
N204 4558 Phase inverter
PT2315 functional pin
S/N Name of pin Description Remarks
1 REF Reference voltage (1/2VDD)
2 VDD Power supply
3 AGND Analog
4 TREB L
5 TREB R L/R channel treble control pins
6 RIN R channel input
7 LOUD-R R channel loudness control pin
9 LOUD-L L channel loudness control pin
11 LIN L channel input
12 BIN L
13 BOUT L L channel bass control input/output
pin
14 BIN R
15 BOUT R R channel bass control input/output
pin
16 RFOUT R channel output
17 LFOUT L channel output
18 DGND Digital
19 DATA （DATA）control data of sequence
transmission (DATA)
20 LCK Clock input of sequence
transmission
8，10 NC Not connected
3. Flow chart of karaoke signal

When the microphone is inserted, MIC signal is sent via MIC to the transmittal circuit
combined by N201A for amplification. Amplified MIC signal gives CPU a MIC
identification signal after N202A amplification, followed by VD201 rectification and
filtering control triode V200. CPU sends PKM signal, which is of low level, causing cutoff
of triode V103/V105 and enabling output of MIC signal; another way reaches pin 6/11 of
PT2315 after C219/C222 coupling, outputs from pin 16/17 after internal volume and tone
control, mixed into one way and sent to N202B and then reversely send to N203B for
amplification. Signals amplified by N203B are divided into two ways. One way is directly
outputted. The other way is outputted from pin 14 after being coupled by R222/C247 to
PT2399 for internal delayed reverberation adjustment, reversed by N204 and outputted by
mixing with karaoke signal. While OK-R is outputted from pin 14 after being gated by
N205 and superposed to L/R track.
In this circuit, the bass boost network made up of triode V201 connected to the
negative terminal of N202B is primarily for bass boost of 75HZ low frequency signal.
During delay adjustment for PT2399, first control signal is given to CPU, which
controls N207 after being expanded via N211 IC CD4049 and connects with pin 6 of
PT2399 by selecting different resistance values for purpose of delay adjustment.
Reverberation control is to change the resistance value at the connection point to R229,
so as to change the superposition on through connect signal for reverberation control.
The broadband processing control signal of SOK’s karaoke is in broadband mode
when it is of high level, when the signal of OK-R is the OK signal inverted by N204A.
A sense signal of OK-SW on the MIC plug conducts MIC signal detection together
with the network made up of V200. When MIC is not plugged, it is of low signal; when
plugged, it is of high signal.
Karaoke auto mute is also available. When P-KT fails to detect signal for a continuous
time, CPU will send a P-KM signal to mute karaoke and avoid MIC receiving noise, which
may affect on sound effect.
 Signal flow chart of profiles
MIC
N
201
N
200
N
202
B
N
203B
N
209
N
204
N205
N
207
N
208
N
100 Karaoke
mixed output
N
202
A
V200
CP
Pass

AV215T (RU) has a special function that switching between 5 profiles is available
without karaoke. Its flow chart is as follows:
When pin 9/10 are of high level, sampled L/R/C signals are outputted via pin 3 N205
gating, and sent to the internal of PT2399 after amplification by N203B for reverberation
delay adjustment (by IC CD4049), and then superposed to L/R/C track to form different
profiles.
In this circuit, MIC shall not be inserted and is only available in 5.1CH mode. N203A
is for the purpose of reversal.
In addition, this device is added earphone output function. PHSW is low level and
each track has output when earphone is not inserted. But when earphone is inserted, PHSW
will be high level for the mechanical settings thus LRM and SCM signal change into high
level at the same time and realize muting in each track, so the signal is only outputted from
earphone, i.e. there is no signal output with each track when connecting with earphone
output.
II. Bass enhancer circuit
P-BURST is the switch signal of burst driver. When it is of high level and added to the
base electrode of V102, V102 will be switched into conduction. When the collector
electrode outputs low level, V107 will be cut off; when the collector electrode is of low
level, V107 will also be cut off. SW signal is normally outputted to external terminal.
Meanwhile, the high level signal of P-BURST is added to the emitter electrode of V108.
V108 is positively biased and switched into conduction. The collector electrode adds high
level to the base electrode of V101. V101 is positively biased and switched into conduction,
CD4094
N
205
N
203
B
N
209
N
207
N
208
N
204
B
Mixed output
N
204
A

and ground SW signal, not superposing it to L/R track signal.
In reverse, when P-BURST is of high level, V100 will be switched into conduction and
SWM signal cannot be outputted from external terminal. Meanwhile, V101 is cut off and
SW signal is superposed to L/R track signal.
The burst driver of AV215T (RU) can be divided into three steps. This principle is to
change the volume of burst driver by changing the SW output volume of M62446.
Meanwhile, SWM signal is added to relay via XS9. When the relay is off, SW signal will
be grounded, disabling the output at super bass port.
III. Mixing and amplification circuit of 5.1 signal and karaoke
When L/R track signal of 5.1 signal is superposed with SW signal and amplified by
N101B/N100B, it is sent to the reverse phases of N101A/N100A. Meanwhile, OK-R/OK-L
signals are also respectively added to the reverse phases of N101A/N100A. After mixing
and amplification by N101A/N100A, they are outputted respectively from pin 1 of
N100A/N101A to power amplification circuit for power amplification.
Meanwhile, the C-1 signal sent by volume board is added to the reverse phase of pin 6 of
N102B and added to the reverse phase of N102A after amplification. Now C1-1 signal after
electronic reverberation processing is also added to the reverse phase of N102A and sent to
power amplification circuit after mixing and amplification.
SR-1/SL-1 of another volume board is also added to the reverse phases of N103B and
N104B for amplification and then sent to N103A and N104A for further amplification, and
later sent to power amplification circuit.
One way of 5.1 signal being mixed and amplified is sent to power amplification circuit
passing through XS9, and the other way forms DIST (distortion error detecting signal)
signal passing through R111-R113/R142/R145/VD100-VD104, which will be added to
CPU for automatic gain, so as to control volume output.
Section Four CPU Board
Achieve overall control, automatically search input signal and analyze spectrum
1. CPU Overall Control
N100, the overall CPU, is the overall control center, inputting all kinds of control
instructions to controlled circuits to achieve all kinds of control functions. It adopts +5V
supply with pin 40 as its supply pin. Pin 18 and pin 19 connect externally with 12M crystal
oscillator to provide working clock frequency for itself. Pin 9 is its reset pin. When starting,
+5V charges C106 via R100. The voltage of two ends of capacitance cannot be mutated,
thus B-pole of triode V100 is low level, that is, V100 conduction gives a high-level reset
signal to CPU. When capacitance C106 finishes charge, V100 stops and then reset finishes.
The form of this reset circuit is to reset high level and keep low level.
When the machine is working, the static information of start log in the screen and
Chinese characters are stored in CPU internal static memory. N101, a status memory, can
record the current working status of machine when cutting off and show the status when
next starting up, avoiding users to re-adjust. The sound mode set by users is also stored in it
and can be activated when necessary.
Ⅱ. Detect Input Signal and Automatically Search Circuits

DISPLAY signal from volume board is sent to N103A to amplify and limit level, then
sent to inverse end of voltage comparator N103B after capacitance coupling. It inputs from
pin 7 of N103B and then is sent to pin 16 of CPU via VD103, V101, R109 and R107.
When N103B inputs a high level, VD103 is in reverse cut-off status, B-pole of switch tube
V101 is high level and is in conducting status, then gets an about +5V high level (signal
input) to CPU after VD101’s stabilization and stop searching. When the output end of
N103B outputs a low level, VD103 is in conducting status, B-pole of switching tube V101
is low level and is in cut-off status, and then CPU detects the low level (no signal input). Its
working principles are:
①After starting up, under CPU internal program’s control, a data signal is outputted via
pin 23 to M62446, and then M62446 scans each input port of N101, N102 and N103 by
emitting high and low levels. When the input ports have no signal input, it automatically
becomes standby status. When any of ports has signal input, track paths of input N101,
N102 and N103 has A/C signal which is amplified and limited level by N108B and N103A
of CPU board, then compares with pin 5 of N103B and gets plus-minus level close to
supply power. The co-phase voltage of N103B is about 0.1V. After the direct current
voltage is over 0.1V, the output end of N103B outputs low level is close to negative-power
voltage, VD103 positive-bias conducts, switch tube V101 (S9014) stops, emitter outputs a
low level to pin 16 of CPU which by controlling IC M62446 makes search level lock on the
port through which signal inputs, to enter normal play.
②When pressing “search” key of remote controller, it is converted from optical signal to
electric signal by the remote receiving head of panel. Pin 14 of CPU emits a high level to
conduct V102 and search according to the same previous process.
Ⅲ. SpectrumAnalysis Circuit (see the following illustration)
Spectrum analysis circuit is divided into three parts:
7-segment
band-pass filter
N
102B
N
104
CD4051
Gain
adjustment
of
automatic
spectrum CPU
V105 Pin 12 of CPU
V104 Pin 28 of CPU V103
+5V .
-
N
102A
A/D conversion
}
DISPLAY +
.
N
108
CD4051
Frequency-
point gating
35HZ
134HZ
300HZ
1KHZ
2.2KHZ
6.3KHZ
16KHZ
}
CPU
N
105C
3
3
+

1. Automatic spectrum gain adjustment circuit: To avoid two situations that spectrum
display amplitude is too low when input signal is too weak or spectrum display is in full
screen when input signal is too strong, AV215T (RU) sets automatic spectrum gain
adjustment circuit, using a single-track one-from-eight electronic analog switch, its true
value diagram is as follows:
Its main working principle is to change the value of inverse ground resistance of transmittal
N104 to change the transmittal gain multiple. Let’s see the detailed work of the whole
circuit. We’ve referred that spectrum analysis signal source (display) is sent to the co-phase
input end of transmittal N105C to amplify. Its amplification factor is determined by the
value of the resistance connecting with the electronic switch of its inverse end N104. When
the main volume is large, CPU will automatically increase the value of ground resistance
and decrease the amplification factor; when the main volume is small, CPU will
automatically decrease the value of ground resistance and increase the amplification factor.
2. Frequency-point gating circuit: signal amplified by N105C is sent via C115 coupling
to seven band-pass filters composed of transmittals. By setting its capacity of feedback
capacitance, its frequency-band range can be determined. The frequency value of
superscript of the output points is the central frequency-point of the frequency band. The
output end of each band-pass filter is connected with a half-wave rectifier circuit. The
amplified A/C signal is rectified to direct current. The circuit is mainly to achieve
frequency-point sample. It can display the amplitude of all frequency-points of the whole
sound signal via direct-current voltage. If the low frequency of sound signal is stronger, the
current voltage of output end of 35HZ and 100HZ band-pass filter is higher. When high
frequency is stronger, the current voltage of 10K and 16K band-pass filter is higher. The
output ends of the seven band-pass filter are connected with the seven input ends of
electronic switch N108 (CD4051). These electronic switches will quickly circularly-switch
among frequency points (referring to previous true value diagram). Pin 3 output end of
N108 will output a string voltage value representing frequency point signal amplitude (see
next diagram).
35HZ 100HZ 300HZ
1KHZ
3KHZ
10KHZ 16KHZ 35HZ
T
V
N
ote: The voltage amplitude
in diagram is uncertain.
A
B
X0 X1 X2 X3
0
0 0
0
1
1
1
1
CD4051Truth Table
0
0
X4 X5 X6 X7
1
0 1
1
0
1
C 0 0001 1 1 1

3. A/D conversion and output circuit display (two situations):
1. When no signal input, pin 28 of CPU sends a high level to B-pole of V104. The positive
end of N102B is low voltage, the inverse end of N102B gets partial voltage of R189 and
R172, making N102B output a low level, that is, triode V105 stops and C-pole of V105
will give a high level to pin 12 of CPU to let CPU not conductAD conversion (pin 6/7/8 of
CPU are inactive and keep high level).
2. When the machine has detected the signal (the inverse end of N102B has a current
voltage representing 35HZ signal amplitude), pin 28 of CPU is converted into low level
and +5V voltage charges for C137 via V103. When reaching the voltage value of inverse
end, the comparator converts and N102B outputs high level. Once CPU receives
low-level signal, it stops 35HZ level gating and converts into next frequency point
100HZ. During conversion, pin 28 of CPU outputs an instant high level to conduct V104,
leak the voltage capacity of C137 and make the co-phase end of N102B restart to charge
100HZ from 0-level. When the charge of 100HZ finishes, the charge and discharge of
next frequency point begin, and such process occurs circularly under the control of CPU.
The charge time form 0-level to the occurrence of output conversion represents the
signal amplitude of current frequency point—the larger the amplitude, the longer the
time and the amplitude displaying in screen is higher; the smaller the amplitude, the
shorter the time and the amplitude displaying in screen is lower. Digital pulse outputted
from N102B output end is added by V105’s inverse to pin 12 of CPU which handle it
and output to panel to display dynamic frequency in screen. The display of original
frequency points is sequential. However, the above circular process is extremely quick,
thus, what we see in screen is the progress of the whole spectrum displaying
synchronously.
Section Five Control Panel
The panel control circuit is the window for man-machine interaction. It can communicate
V
T
35HZ
100HZ
Interval of switch
V
T
35HZ 100HZ
Time for charge Time for charge
Dischar
g
e of hi
g
h level
(Fig 6)
Frequency-
p
oint circle
gating period

the operation command with CPU to finish kinds of artificial operations. At the same time,
it is the window of the complete machine by which human can predominate the complete
machine’s working status. It is also an important element to its appearance. The AV215T
（RU）panel control circuit block diagram are showed as follows:
(1) Power supply circuit
1. AV215T (RU) has two groups of voltage of +3.3V and +5V in control panel.
Voltage of +5V after voltage stabilization from signal panel supply power to N102,
N103, IC CD4013 and N101 PT2222 after voltage reduction via two diodes of
VD105、VD106、VD107、VD108.
(2) LCD display driver and button circuit
This circuit is made up of N101, N102, N103 and LCD.
Working principle: display of this device is directly controlled by P0 interface of CPU
and IC is bound inside of LCD. Working voltage of display is 3.3V and voltage of
control line sent out from CPU is 5V, so the level between CPU and LCD display is
transferred via two ICs of 74VHC245 thus control the display screen by transferring
control level of 5V from CPU to 3.3V.
Button circuit of this device is an equivalent to remote controller. After being
received by PT 2222, signal of button matrix controls the conducting degree of triode
V100 via pin 7 thus makes the signal sent by diode VD100 of infrared luminescent and
processed by CPU after being received by receiver of remote controller.
Section Six Power Board
LCD display
Power supplyDrive circuit
Button
Remote-control
CPU

It is used for providing all kinds of needed working voltage for units of the whole
machine. AV215T (RU) adopts a ring transformer with 335W power. The middle and
surround channel of AV215T (RU) respectively adopt LM1875 and LM1876.
LM1876, the dual-channel power amplification IC, supplies power by separate
positive power, ensuring there is high separating degree between two surrounds. It
adds ±VSS supply comparing with previous machines. The diagram of power supply
circuit is as following:
1. Two A/C 38V of transformer first level output is rectified and filtered by four
IN5404 and two big electrolytic capacitors (15000uF/68V) and gets plus-minus
53V power to supply for right and left channels.
2. Two A/C 21V voltage outputted by second level of transformer is rectified and
filtered by four IN5404 and two electrolytic capacitors (4700uF/35V) and gets
plus-minus 28V power to supply for SL/SR/C channels. Other ICs and operational
amplifiers are stabilized by stabilizing tube L7812 and L7912 and gets power to
supply for other IC.
Section Seven Power-amplification Board and Protective Circuit
Ⅰ. Power amplification circuit of L and R channels: L and R main power amplification
circuits of AV215T (RU) are composed of separate elements. The block diagram is as
following (taking L channel for example)
Panel
display
Filament
voltage
Rectifier
filter Power-amplifier
stage of righ
t
and left channels
Power-amplifier
stage of C, S
L
and SR channels
～16.3V
～26V
～2.2V
～38.5V
～220V50HZ
Rectifier
filter

L-track signal is sent by coupling of R101, R103 and C101 to B-pole of differential
amplification stage V102. V102 and V103 compose of differential amplification circuit of
single-end input and output. Speech signal is outputted from C-pole of V102 to B-pole of
voltage amplification stage V105, and then to compound power amplification stage after
amplifying voltage. V104, V107, VD102 and VD103 compose of image constant-current
source circuit. VD102 and VD103 provide constant base current for V104 and V107. The
emitter resistance of V104 defines the working current of differential amplification stage
and the emitter resistance of V107 decides the working current of voltage amplification
stage. V132 and V112 compose of compound tube amplification, making the final stage of
power amplification with strong current amplification, which compose of wave plus
half-circle amplification. V133 and V113 compose of wave minus half-circle amplification,
whose circuit structure is completely the same to the previous tube. Two functions of
temperature compensation tube V106 are: firstly, it is the base-level bias of upper and
lower tubes. Its working status determines the static working current of compound power
amplification. That is, we can set the static working point of compound power
amplification stage by adjusting V106 conduction. The common way is to change the base
resistance of V107. It can also automatically adjust the working status of compound power
amplification stage when the temperature arises. The adjusting process is:
Total current of output stage = working current + leakage current
When temperature arises, leakage current also arises, causing the static working point flow
(bad). At the same time, the leakage current of V106 arises and Uce decreases, causing the
bias current of output stage decreases, working status changes and working current of back
pole decreases, in order to compensate temperature.
Voltage negative feedback is introduced in power amplification circuit of AV215T (RU),
composing of R121, R109 and C105, stabilizing the static working point of differential
stage. AV215T (RU) adopts direct output. R111 and C116 of its output end compose of
Zobel Filter, preventing high-frequency self-excitation caused by A/C inductive reactance
of loudspeaker speech coil.
Ⅱ. The principle of R-track is same to that of L-track. No more words here.
L IN
Differential
amplification
level V102, V103
Voltage
amplifi
cation
stage
V105
Image constant-current
source V104
,
V107
,
VD102
,
Temperature
com
p
ensation level V106
Compound power
amplificationV133，
V113
Compound powe
r
amplification V132，
V112
S
p
eaker
A/C negative feedbac
k
R121, R108, C105
.
V101
V115
Mute
Rela
y

Ⅲ. Mute circuit: when pressing mute key of remote controller, a photoelectric conversion
mute signal by remote receiving head is sent to CPU, whose pin 35 and 36 emit a
high-level mute instruction to conduct V115, V101 and V116 and L and R-track signal
short pass ground, achieving the mute control.
Ⅳ. C, SR and SL power amplification circuit: Compared with previous machines, these
three tracks of AV215T (RU) adopt special power amplification LM1876 and IC LM1875.
LM1876 has 15 pins. The pin 2, 15 and 4 are respectively its plus-minus power pins. The
pin 7/8/12/13 are its co-phase and inverse input ends. The rated output power of each track
of the power IC can reach 20W with automatic mute function when starting up. 1875, five
pins, is a power amplification IC with better performance and extremely simple application
circuit which has 15W power output in rated status. Its pin 5 and 3 is plus-minus power
supply pin.
V. Protective circuit
The protective way of L, R and C tracks is to cut off relay Y100 when starting up to cut off
its output. SR and SL tracks protect by mute. AV215T (RU) has functions of starting delay
protection, mid-point over-voltage and over-current protection and standby protection.
1. Starting delay response protective circuit: because the circuit is unstable when
starting up and its dash current does great harm to sound box and power
amplification circuit, the delay response protective circuit is set. There are two
steps for starting delay response protective circuit: Firstly, C, L and R. Its working
process is: the A/C of transformer is rectified and filtered by VD113 and C110 to
form a 22V voltage, then R108 charges C115 to inversely breakdown VD111 and
V105 and V104 forward conduct, finally the Y100 responses and delay forms.
Secondly, L and R surround tracks take starting anti-dash protection by following
ways: when the system resets, pin 33 of CPU outputs a high level, passing R164 to
pin 9 and 14 of LM1876 which outputs mute. After machine succeeds in delaying
starting, pin 33 of CPU switches into low level and SL/SR path normally outputs.
2. Mid-point over-voltage protection: the output end of each track is connected with
a SL are respectively R119 and R120. As long as any mid-point voltage of tracks is
over +3.5V or lower than -3.5V, V101 or V102 conducts to decrease their C-pole
voltage, then V103 conducts to finally cut off relay to protect circuit starting.
Each channel is
connected wit
h
a over-voltage
sampling
resistance
L-channel
is R116
Over +3.5V
Lower than -3.5V
V101 conducts
V102 conducts
C-pole
voltage
decrease
V103
conduct
Cut off relay to
p
rotect circui
t
starting

3. Over-current and short-circuit protection: output load resistances of L- and
R-track are connected with an over-current sampling triode. The sampling tube of
L-track is V114 and load resistance is R126 and R127. The power amplification IC
of other three tracks has functions of over-current protection. As long as
over-current occurs in L-track, the voltage drop of R126 and R127 will rapidly
increase. Once the voltage drop of R129 is over 0.7V, V114 will conducts, and then
V103 conducts and finally relay cuts off to protect circuit starting.
With the same manner, voltage of R159 will be over 0.7V to conduct V129, then
conduct V103 and finally cut off relay to protect loudspeaker.
4. Energy-saving protection: when standby time reaches 10 minutes and still needs
continuing, CPU pin 34 output PRC signal is high level which saturates and conducts
V100 via VD108 and R101, then conducts V103 and finally cuts off relay to save
standby energy.
Maintenance and Repair Flow
Ⅰ. Malfunction Phenomenon：Sound fault
Analysis：Generally, such fault can be checked by signal injection step by step. If the
speaker of any step has no disturbance, there must be problems with this step. In general,
this method should be carried out from rear step to front step. Another method is signal
detection, which is carried out from front step to rear step. If there be no sound with any
step, this step must be the fault point. Specific examine and repair flow for this fault is
showed as follows:
Each channel
is connecte
d
with a
n
over-current
sampling
triode
L-channel
is V114
C-pole
voltage
decrease
V103
conducts
Cut off rela
y
to protec
t
circuit starting
The voltage
drop of R126
and R127
increases
when
over-current
V114co
nducts

N
o
N
o
N
o microphone
Check C219，C222 to confirm i
f
there be sound or not Check circuit for N210 an
d
microphone
Check R219 and R220 to confirm i
f
there be sound or not
上有无声音
Check PKCK, PKDA signal o
f
PT2315 and CPU
Check R215T to confirm i
f
there be sound or not Check N202 and its power supply
circuit
Check C245 and C246 to
confirm there be sound or not Check N203 and its powe
r
supply circuit
Base electrode of V104 and V105
is 0.7AV or not?
Check if V104 or V105 have
been brokendown or not
The E-electrode of V103 is hig
h
level or not?
MICDET be high level? PK
T
be low level? CPU fault
Microphone fault
V200 fault
V103 fault
N
o
N
o
N
o
N
o
N
o
Yes Yes Yes Yes Yes Yes

Ⅱ.Fault phenomenon: No spectrum display
N
Y
V105 itself and its power supply is
normal or not? Check power supply, V105
and peripheral circuit
N
VD118 is normal or not?
OK
N
Replace
VD118
If there be any change between high level
and low level on collect electrode of V105 Check CPU an
d
I2C bus
OK Check the circuits
with V103 and V104
N
o spectru
m
display
N
102B forward terminal
voltage jump or not?
N
OK
N
102B reversal has high
level and low level or not? Check N102 an
d
peripheral circuit
N
N
108 and CPU control pin
work properly or not?
OK
Check control signal, N108
and peripheral circuit
N
Check the auto-gain regulation circuit made o
f
seven-segment band-pass filter, C115 and N105
OK

Ⅲ. Fault phenomenon：Automatic search fault
Automatic searc
h
fault
DISPLAY signal be delivered to
103A reversal or not?
N
Check spectrum sampling an
d
amplifying circuit, N103 an
d
N108B
Y
Voltage be supplied to N103B
reversal or not?
N
Check N103A amplifying
circuit and power suppl
y
Co-
p
hased terminals of N103B
are low level or not?
Y
Check N102 an
d
peripheral circuit
N
Y
VD103 be normal or not?
N
Replace VD103
Y
Check VD101, CPU, V101 an
d
peripheral circuit