BBK AV100 Service Manual

AV100 Maintenance Manual

l Precautions:

High voltage inside. Disconnect the power cord from the power supply before servicing! High voltage components inside. All warnings and instructions on the device shall be followed upon servicing. Components to be replaced upon servicing shall conform to the specifications. To avoid any danger, do not attempt to modify the parameters of components!

I. Circuit Connection Diagram

II. For the description of operating modes, see User’s Manual

Section 1 Device Structure

The entire device of AV100 can be divided into five constituents:

I. Power Supply:

Provide required working electrical power to element circuits including main channel

with

circuit with

power amplification circuit, central/surround channel amplification circuit, display element circuit, small signal processing circuit and overall control circuit.

II. Signal Processing (including input, cyber logic, bass enhancer and volume control circuit,

small signal amplification circuit):

Fulfill selection between input signal sources, cyber logic, bass enhancer, small signal preamplification and independent electronic volume control over channels. “B ass enhancer” function is unprecedentedly added to AV100.

III. CPU Control

Being the control and processing center of the entire device, it consists of CPU, panel control and software recognition circuit, providing users with a “man-machine conversation” environment, so as to fulfill process control, protection function control and frequency spectrum display.

IV. Microphone Circuit

It consists of small signal preamplifier circuit and echo processing circuit, and will finally be sent into the preamplifier of main channel and main channel for mixed amplification

V. Power Amplifier and Protection Circuit

Conduct post power amplification for small signal. Meanwhile, conduct automatic protection for power amplifier circuit and speakers.

Section 2 Power Circuit

It provides working voltages required by circuits of the different units. See different levels of

transformer outputs below:

I. The DC power supply of ±32V is obtained via the rectification and filtration of two

sets of AC 26.5V outputted from the transformer at first sublevel by four IN5404s

Provide PT6311 with drive power

Provide display

Provide main power amplifier

Provide SL/SR/C with power supply

and two big electrolytic capacitors (4700uF/35V), providing power to left and right

channels.

B X0 X1 X2 X3 0 0 0 0 1 1 1 1

Truth

1 X B Y C 0 X1 1 Y0 0 Y1 0 1 X0 Z Z0 Z1

Truth

II. The power supply of ±22V is obtained via the rectification and filtration of two sets

of AC 16V voltages outputted from the transformer at second sublevel by four IN5404s and two electrolytic capacitors (2200uF/25V), providing power to SL/SR/C channels, and also to other IC and operational amplifiers after voltage stabilizing via

voltage stabilizing tubes L7812 and L7912; AV100 is provided with standby function, using CPU software program to mute all channels in standby mode.

Section 3 Input, Cyber Logic and Volume Control Circuit

The cyber logic function of AV100 is realized by C/SR/SL and SW channel signals obtained after processing signals extracted on L/R channel by using low pass filter and band pass filter. This circuit uses several electronic analogue switches to fulfill switching between different modes (See Figure II for signal flow).

I. Input selection and mode switching circuit

AV100 has two sets of analogue audio source input modes and a set of 5.1 input jack. The switching between them is realized by using electronic switch. Two types of electronic switch IC are used in the circuit: CD4052 (2-channel 4-option electronic analogue switch) and CD4053 (3-channel 2-option electronic analogue switch). Their truth tables are as follows:

CD4052

CD4053

In this circuit, there are another two important control signals, i.e. SEL and MUT1. When SEL is of high level, the circuit is in external “5.1 channel” input mode; when SEL is of low level, the circuit is in “Cyber Logic” mode; when MUT1 is of high level, “Bass enhancer” function will be enabled; when SEL and MUT1 are all of low level, the circuit is in standard sound field processing mode. Here is a detailed analysis:

When pressing “input” button, IC SC0791 on the control panel will recognize its code and send an execution request signal to CPU. Then the 32nd pin of CPU (N100) will return a data signal to M62446. According to the “input” button status, the 1st/2nd/3rd/4th pin of M62446 sends corresponding high/low levels, the combination of which will enable electronic switch to circularly select between VCD? DVD? 5.1CH. Now there are mainly two statuses: two analogue input statuses (VCD/DVD) and 5.1CH input status. Their respective signal flows are as follows:

1. 5.1CH input status: When A/B/SEL control lines of M62446 are o f high level, L/R channel

108B N1

03A

N106

volume

N103

electronic

switch

N102

electronic

switch

5.1 input

105A

107A

signal of 5.1 input end is outputted from pin 3,13 of N101 and sent to IC N106 for functional adjustments of channel volume, sound field balance, etc.; meanwhile, the 4th pin of N106 outputs a high level to pin 9,10,11 of electronic switch N102 (i.e. SEL control s ignal), and C, SR, SL signal on

104B

VCD

L/R channel

5.1 input C/SR/SL channel

5.1input SW

N101

CD4052

Input

selection

SL SR

SW1

CD4053

104A

107B

CD4053

105B

to L/R

SW C

103B

M62446

electronic

control

100

CPU

（Fig. 2）

5.1 input terminal is respectively sent from pin 14, 15, 4 output of N410 to IC N106 for independent volume control. SW channel signal on 5.1 input terminal is sent to pin 3 of IC N103, while pin 9 (SEL) is of high level, and SW signal is sent from pin 4 output to IC N106 for volume control. Now the six channel signals of 5.1 input terminal are all sent to electronic volume control IC for independent volume control and then outputted post pole circuit. The signal source of the device is in 5.1 channel input mode.

2. Two analog input modes: Press the input button on the panel to select from two analogue input modes of VCD and DVD as signal source. The selection is also realized via data signal sent from pin 32 of CPU N100 using pin 1, 2, 4 of M62446 to send three control levels of A, B and SEL to pin 9, 10 of electronic switch N101 (pin 9, 10, 11 of N102). L/R channel signal is subject to volume/tone control and sound field mode directly via M62446 from pin 3, 13 output. AV100 has three processing modes for signals: hi-fi, cyber logic and standard sound field. Their respective signal flows are as follows:

1) Standard sound field processing mode: L/R channel signals outputted from N101 are directly added to IC N106 for electronic main volume control. Meanwhile, SW signal obtained by amplifying a signal from L/R channel via N104 voltage followed by N107A two -level low pass filtering is added to pin 6 of electronic volume M62446 for electronic volume control. MUT1 is of low level; now the device is in 2-channel input and 3-channel output mode. When MUT1 is of high level, “Bass enhancer” function is enabled. Now the device is in 2-channel input and

2-channel output mode.

”

button for

analog

sound

Logic

available

; sound field and

Only L/R/SW channel

music

hall

sound field and balance

, theater

sound field and balance

, theater

field and balance

2) Hi-fi processing mode: (mainly for VCD/DVD input mode): The signal flow is same as that of stand sound field mode, but under the control of CPU, electronic volume control IC N106 closes other channels and disables sound field processing and balance control. Therefore, SW/C/SL/SR channel has no output and the device is in 2-channel input and 2-channel output mode.

3) Cyber logic mode: L/R channel signals outputted from N101 are directly sent to IC N106 for electronic main volume control. Meanwhile, two ways of surround channel signals are obtained by adding and subtracting using N105（4558）after amplifying two ways of signals from L/R channel via N104, central channel signal is obtained though N105A, and SW signal source is obtained though N107A inverse amplification, and is inputted to pin 6 of M62446 (Note: SW signal of cyber logic is obtained through the output terminal of M62446 and then through a 2nd order low-pass filter); now pin 9/10/11 (SEL) is of low level and SW signal source is directly sent to pin 6 of M62446 for electronic volume control. MUT1 is of low level, and now the device is in 2-channel input and 6-channel output mode; when MUT1 is of high level, “Bass enhancer” function is enabled and now the device is in 2-channel input and 5-channel output mode.

The relations between switching between aud io sources of input circuit and sound processing modes are as follows.

Hi-fi mode

Only L/R channel output

Two

Standard

output is available,

Press “input

Cyber

“Bass enhancer” is enable 2-channel output

5.1CH input

“Bass enhancer” is enable 5-channel output sound

6-channel output , theat

II. Volume control, sound field processing and EQ control circuit Channel signals are finally sent into N106 to fulfill independent volume control, EQ control and

different sound field mode processing, etc. Sound field processing and EQ control circuit is mainly for the processing of L, R main channel signals. As seen from the schematic diagram, L, R channel signals are sent to pin 13, 15 of N106. When the device is in hi-fi mode, CPU software program will control M62446 and mute other channels, and volume control is only available for L, R channel, and only pin 31, 32 has signal output, while the device is in 2-channel output mode; when the sound field mode of the device is not in hi-fi mode, independent volume control of each channel and sound field processing or EQ adjustment of L, R main channel are available. Finally, signals of different channels will be

outputted from pin 31, 32, 33, 34, 35, 36 of N106. SW channel signal outputted from pin 36 will be sent into pin 1, 12 of N103 after passing an active low pass filter. The level signal of MUT1 will decide whether outputting it to an active speaker for amplification by SW output terminal or sending it to main channel to enable “bass enhancer” function. Other channel signals will be sent into power amplifier circuit for post power amplification. L, R channel signal will pass two-level mixed amplification (superpose subwoofer or karaoke signal onto L/R channel).

“B ass enhancer” function:

”B ass enhancer ” function is to send subwoofer elements to left and right channels respectively so as to enhance the bass effect on main channel. At this time subwoofer speaker has no output and an active subwoofer speaker can be saved; but this will increase the power load on main channel, placing a high requirement on post amplifier. Primarily comparing with standard sound field, cyber logic and 5.1 input sound field mode, its operating principle is as follows:

When the device is in any of the three modes and “Bass enhancer” function is enabled, CPU will send a data signal to IC M62446, pin 32 of which will send a high level signal to pin 10, 11 of N103, so that pin 14 of N103 will be grounded (signal outputted to SW is closed), and SW signal will be outputted from pin 15 of N103 to the reverse phase of N109A/N109B for mixed amplification with L/R channel, followed by post amplification in main channel power amplifier circuit after N110 amplification. For the three modes of “Bass enhancer”, gradual volume increase is done by IC M62446 and each time an increase of over 3dB over the previous grade is done.

III. Input signal detection, search and spectrum sampling circuit

1. Input signal detection, search circuit: After synthesizing and gating, input signals are mixed by

sample resistances R133, R134, R135, R136, R195 connected to the output terminals of N102 and N103 and then amplified at the inverted input terminal of N108A. Then input signals are level amplified and clipped by N103A on CPU board, and then sent into voltage comparator made up of N103B. The output terminal of N103B is connected to pin 16 of CPU through a triode (switch tube). When the output terminal of N103B outputs a high level, VD103 is in inverse cutoff state and the E pole of switch tube V101 is of high level. Therefore, the switch tube is in conducing state. Then through voltage regulation by N103B, an obtained high level of about +5V returns to CPU, indicating no signal input is detected; when the output terminal of N103B outputs a low level, VD103 is in positive conducing state, and the E pole of switch tube V101 is of low level. Therefore, the switch tube is in cutoff state. Through VD101, a low level returns to CPU, indicating there is signal input; when it is of low level, CPU stops searching. See details below:

1) After startup, pin 32 outputs a data signal to M62446 under the control of CPU internal program,

and then M62446 sends high/low level to scan each input port of N101, N102, N103. When none of these input ports has signal input, it will automatically stop in VCD mode (display the previous off state “connect to ***”). When one input port has signal input, and this signal is greater than about 15mV, AC signals will be present on channe ls of N101. This AC part, after N104 amplification and amplification on N105A, N108B and N103A on CPU board and level clipping, is compared with pin 1 of N103B and then a high/low level of power supply is obtained. Now the positive voltage is about 0.35V. When this DC voltage exceeds 0.35V, the output terminal of N103B outputs low level close to negative supply voltage, so switch tube V101 (S9014) cuts off. Through VD102 and R109, a low level returns to pin 16 of CPU, indicating CPU has searched signal, the CPU locks search level on this port with signal input via controlling IC M62446 and enters into normal playback.

2) When “search” button on remote control is pressed, optical signal received by remote control

+ 12 hidden pages