KALAOKE circuit principle
1) The microphone input is introduced by two microphone seven-pin sockets, and the microphone output signal is shorted to GND when the microphone is not plugged in. Only when the microphone is plugged in, the microphone output signal will be disconnected from GND and effectively output to the subsequent amplifier. The circuit diagram is not shown. The 7-pin microphone has a set of switches. The microphone is not inserted, and the output is short-circuited to the ground, which has the effect of suppressing noise. The microphone will automatically short open and the audio path will be unblocked. Let's find a 7-foot seat and study it.
2) After the microphone input signal passes through the positive phase amplifier tube of the IC1A dual op-amp side amplifier, the 50K single potentiometer (2W1) realizes the attenuation adjustment of the microphone MIC VOL, and the microphone signal after volume adjustment passes through the first-level common emitter amplifier circuit, The other side of the IC1B dual op-amp is also inverted and amplified, and the microphone signal finally enters the RSM2399 for reverberation (ECHO) processing. Adjusting the resistance value of the resistance under the 6 feet of 2399 can change the reverberation delay time. Generally, the standard is to hear 7 consecutive echoes that fade away.
3) RSM2399 can process the delay effect of the audio signal, please refer to DATASHEET of PT2399 for the connection of peripheral components.
KALOKE circuit maintenance
1) MIC microphone circuit failure: the microphone is silent and has no output.
A) Check the power supply of the MIC circuit
In the maintenance procedure, first, confirm that the power supply of RSM2399 is normal. The voltage of the PIN1 pin of RSM2399 to the ground is 4.7Vï½5V, and it is 5V when there is no signal input. It is also necessary to confirm that the power supply of the microphone IC1 dual op-amp is normal.
B) Check the MIC signal path
Input the MIC signal (insert the microphone to test and test at the same time), and use the oscilloscope to observe whether there is a coupled signal output from the C15.
If C15 has no signal output, it means that the fault is in the MIC dual op amp IC1 amplifying circuit. It is necessary to check the IC1 amplification, whether the power supply is abnormal or the coupling electrolysis is open, the volume potentiometer is soldered, the signal is short-circuited, etc., and the fault can be eliminated.
If C15 has a signal output, it means that the RSM2399 input signal is OK, but RSM2399 has no output. First, check whether the 2C11 coupled signal is shorted to the ground due to a defective microphone socket. Otherwise, check the RSM2399 peripheral circuit and RSM2399 quality.
Note: If the microphone is plugged in and the output signal is still shorted to the ground, the microphone socket is defective and must be replaced. In the normal state, if the two microphone plugs are not plugged into the microphone, the signal will be shorted to the ground, and any one of them will be shorted to the ground.
2) MIC circuit failure: noise when adjusting MIC VOL or ECHO
The maintenance steps should focus on the quality of the MIC VOL/ECHO potentiometer. Check whether there is a problem with the internal reed of the potentiometer. You can use special cleaning fluid or industrial alcohol to clean the potentiometer. If possible, replace the bad potentiometer directly.
3) MIC circuit failure: MIC sound is distorted
The maintenance steps should focus on the two operational amplifiers (IC2 operational amplifier mixes the MIC signal and other audio signals with an adder to make the human voice and music superimpose KALAOKE) and the quality of the RSM2399 itself or the quality of the external components. Focus on checking whether their power supply is normal, replace components when necessary, and use the "replacement method" to narrow the problem area until the problem is found and eliminated.
Event date & time: 08.12.2020 at 01:00
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