Aihua combination audio maintenance information function

Single chip microcomputer STM32L151CCU6

MOS power IC full range

Photocoupler

Aihua micro-composite is widely welcomed by the public family because of its full-featured, easy-to-use and good sound quality. At present, such audio has entered the maintenance period. Taking the Aihua NSX-380 stereo as an example, the author introduces the control circuit principle and troubleshooting of this type of machine. The principle and maintenance method described in this paper are also applicable to NSX-330, NSX-360, NSX-500 and other combination sounds on the circuit similar to this model.

Control circuit principle

The NSX-380 stereo consists of three-band radio, dual-card tape recording, single-disc CD playback, fluorescent multi-function display, amplifier, and speakers. The control circuit is composed of a microprocessor (CPU) IC 201 (LC866428V), an eight-bit shift register IC 402 and an IC 403 (both BU4094BF). The schematic diagram of the control circuit drawn according to the physical printing plate is shown in Figure 1.

The stereo has two input modes: one is to input from the machine panel. There are 21 keys on the panel, which are divided into three levels according to the level change from the {30}, {31}, {32} pins of IC201. The volume can be manually adjusted for rotation; the second is operated by the remote control. After the remote control infrared signal is amplified and shaped by IC202, it enters from the {40} pin of IC201, and after decoding, it can achieve the same effect as the first input mode. The display screen shares a block, which can display the radio frequency, the number of tape revolutions, the CD track number and playback time, the audio equalization curve, etc., and the CD and Tape operation keys such as "Play", "Rew", "FF", etc. Just send the function key "CD", "Tape" selection command to the CPU.

After the power is plugged in, the power indicator is red, and the whole machine is in the standby state. When the “Power” button is pressed, the pulse signal enters the IC201. After the internal operation processing, the 8 pin changes from the high level to the low level. The Q421 is turned on, on the one hand, the whole machine is powered, in the ready-to-work state, the power indicator is off; on the other hand, the button indicator is powered, indicating a certain functional state before the shutdown.

All key operations are displayed on the screen, and some buttons are followed by LEDs for indication. The 5 and 7 pins of the CPU of this part function output control signals and clock signals to IC402 and IC403 respectively, and are completed by internal processing of these two ICs. At the same time, they also complete subwoofer, volume adjustment (drive motor rotation), tape high-speed playback control and other functions. For example, when the button selects the “Tape” function, the CPU changes the 4 pin of IC403 from high level to low level, the red light in LED1 is on, and the green light is off due to insufficient voltage; otherwise, it is high level and the green light is long. . LED2, LED3, and LED4 indicate "CD", "Aux", and Tuner respectively, and the principle is the same. When the "Play" key is pressed, the CPU makes the 4, 5 pins of IC402 change from high level to low level, and LED5 green light. Bright; otherwise high level, LED5 does not light. LED6 ~ LED9 work the same process. The {11}, {12} pins of IC403 output different level signals to complete the volume adjustment function, when the {12} pin is high When the {11} pin is low level, Q504 and Q506 are turned on, the motor rotates counterclockwise, and the volume becomes smaller; when the {12} pin is low level and the {11} pin is high level, Q507 and Q508 are turned on. The motor rotates clockwise and the volume becomes louder.

The tape drive of the combination sound changes the control mode of the traditional mechanical movement, and the two movements are driven by one motor, and the sound is particularly small during operation, and there is almost no feeling. When the "Tape" function is selected, the CPU 4 pin changes from high level to low level, Q502 turns on, +12V supplies power to the tape motor and Hall element, and the motor rotates. At this time, the tape does not move and has a playback condition. . If you select the sound box, when the "Play" button is pressed, the CPU 2 pin changes from high level to low level, Q503 turns on, the electromagnet Sol is energized, the magnetic head rises, and the multi-ring shaped groove in the movement Gears, complete playback, fast forward, fast rewind, head reversal and other functions. The same can be used to analyze the working process of the recording and storage bin. The tape running count is performed by the Hall magneto-sensitive element, and after being amplified by the Hall element, the pulse signal is output to the CPU and displayed on the screen, and the display range is 0000 to 9999. When the display data is unchanged (no pulse signal), the CPU considers that the tape has reached the end and issues a command to stop the playback or reverse playback, which is used for the rotation of the two-way recording and playback head.