BBK MA-960S Service Manual

MA-960S Principle and Maintenance

1. Product profile

MA-960S is a medium-grade active speaker consisting of 5 satellite
speakers, that is, one subwoofer speaker, two front speakers, two surround
speakers and one center speaker. The product features excellent sound
effect in appropriate space and it has the following features:

(1) 2.1/5.1CH output;
(2) Visualization 2/5 conversion and volume adjustment;
(3) Built-in 5CH power amplifying, adaptable to AC-3/DTS and stereo music

replay;

(4) With 6CH volume adjustment and independent level control, and with tone

adjustment function.

2. Principle block diagram

Signal

input

Electronic

volume and

tone

adjustment

Power

amplifying

Output

CPU system control

Receiving and display

part

3. System composition

This device comprises input board, output board, power amplification
board and control panel. The input board and output board are only composed
of a few terminals. The main part is power amplification board. System control,
amplification part and power supply are all composed inside. The following is
the brief description of the principles for the power amplification board.

1) Power supply part

In consideration of the big output power of the subwoofer, the device
employs a ring transformer for power supply. A group of 18V (AC) voltage is
outputted from the transformer, which will be subject to rectification and
filtering and will output +22V voltage to power IC TDA8947 and IC TDA9843
for power supply.

One line of output 22V voltage goes through the current limiting resistor

R101, voltage regulating diode VD104 and capacitor C108and then outputs
+9V voltage to IC PT2322; the other line goes through R100 and voltage

regulating diode VD105 and then outputs 5V power supply for the CPU and the
control panel.

2) Signal input, volume and tone adjustment

The device has six channels for signal input. The signals input through

each channel will go through the filtering capacitor before being directly
delivered to the IC PT2322 for volume and tone adjustment. In addition, one
line of signals will be delivered from the L and R main sound channels and
overlapped on the SW input. As a result, 2.1 output effect will be achieved
even when there are only L and R channel inputs.

IC PT2322 is an IC with 6-channel independent volume and tone
adjustment. With its gains adjustable from 0 to 95 signal DB; it is applicable to
home theatre products. With benefits such as big range of power supply, low
power consumption and wide temperature scope, it is quite competent IC, and
the functions of its main pins are listed in the following table:

Pin name Pin number Pin description
FLIN 11 Signal input
FRIN 4 Signal input
RL 10 Signal input
RR 5 Signal input
C 9 Signal input
SBW 6 Signal input
FLOUT 17 Signal output
FROUT 23 Signal output
COUT 19 Signal output
RLOUT 18 Signal output
RROUT 22 Signal output
SBWOUT 21 Signal output
VREF 7 Reference voltage
VDD 20 Power supply
DI 25 Data control line
CL 24 Clock control line

The IC internal unit equivalent circuit:

3). Amplifying circuit part

Principles: as far as the IC PT2322 are concerned, the signals of the main
channel will be delivered to N101 IC TDA9843 for power amplification; the
central surround signals will be filtered and delivered to the N106 IC
TDA8947 for power amplification; the subwoofer signals will first pass
experience amplitude limit (the amplitude limit circuit comprises VD110 and
VD113 diodes) and pretreatment before being delivered to the N102 IC
TDA9843. Amplitude limit is aimed at preventing excessive size of signals,
which may, after amplification, damage the loudspeaker due to excessive
power. Because the power supply of the amplification IC is fulfilled by a
single power source, all amplified and output signals will have DC, therefore,
the signals will still experience filtering before being output to the
loudspeaker.

IC TDA9843J is used for dual channel power amplification. With standby
and mute modes, free from switch impact, and with functions such as short
circuit protection and overheat protection, it can effectively be prevented
from being damaged in case of IC abnormality. In ordinary output mode, the
IC can supply for each channel a maximum of 20W power output. When BTL
output is employed, the power can be as high as 40W. In addition, the IC
features powerful anti-ripple performance, with little power consumption in
the standby mode.

The functions of the various pins of the IC TDA9843J are listed in the following
table:

Symbol Pin Function
IN2+ 1 2nd channel input
OUT2- 2 2nd channel output
CIV 3 Common mode input

signal suppression
1N1+ 4 1st channel input
GND 5 Ground
SVR 6 Reference voltage
MODE 7 Mode selection
OUT1+ 8 1st channel output
VCC 9 Power supply

IC TDA8947J is used for four-channel power amplification. Its features are
similar to those of the IC TDA9843J, however, its output power is bigger, and a
signal sound channel can be as high as 25W.

4). Control circuit

MA-960S employs IC AT89C2051 to serve as its core part to control the
operation of the whole device. With low voltage and high performance, it
employs 8-bit 2K bytes flash and ROM single-chip. Boasting 15 I/O ports
and six interrupt sources; it has features such as low power consumption
and standby mode.

The principle block diagram of the IC is illustrated in the following figure: