Keywords: fault tracing circuit, audio amplifying circuit
When a radio, a recorder, a power amplifier, a combined audio, etc. is repaired, and the application fault tracing can quickly and accurately determine the location of the fault. It has the characteristics of compact, light, easy to carry, as a standing tool for electronic enthusiasts.
First, the circuit schematic circuit is shown in the drawings. When the probe is touched, the received electrical signal is coupled to the base of the triode VT1 via the capacitor C1, and the front amplifier is performed by VT1.
The amplified signal passes through the high frequency choke circle 1 to a straight-parallel two-stage amplifying circuit composed of the triode VT2, the composite tube VT3, and VT4, and is output from the emitter of the composite tube, and the speaker Y is pushed. When the probe is in contact with the measurement point and y silent or sound distortion, it means that the circuit has failed.
Second, the selection component VT1, VT2 is high gain triode 9014, penetration current is small, β>80; VT3, VT4 is 9012, and the beta value can be selected between 50 and 1 y00. Inductance 1, capacitor C2 constitutes a high frequency filter circuit, 1 selected from the color code inductance of 10MH, and the model is 1H2A, and other types of color code inductors can also be. LED VD can be optionally selected. The speaker starts a monitoring.
You can choose 8Ω / 0.1 Wo-type paper pot speakers, RP is used to adjust the signal size, and the resistance is 5.1kΩ, requires and switch S. The probe can be converted with a large beast injection needle or a small universal table pen.
The parameters of other metades are marked in the figure, no special requirements.
Third, the VT1 and VT2 work points adjust the part of the circuit that needs to be adjusted in this circuit is the static work points of VT1 and VT2. First, first, the potentiometer RP is first rotated in a moderate position, and a signal generator is selected, the frequency is 800 Hz to 1 kHz, and the level is in the range of -14 to 0 dB. The probe comes into contact with the output of the signal generator, connects the crocodile clip and the signal generator ground. If there is no signal generator, the probe can touch the collector of the radio active triode triode. The crocodile clip receives the pitch supply negative or "ground". When the radio is tuned, the speaker Y can hear the broadcast.
Adjustment of VT1 Static Work Point: When there is a weak signal, the VT1 is in a saturated state, adjusting the resistor R1, the signal gradually increases, then the VT1 collector potential VC1, gradually increase, until the sound is clearer, at this time IC1 For about 0.6 mA, the VT1 is in an enlarged state to stop adjustment. Be careful not to allow VC1 to rise to the proximity of the power supply, otherwise the VT1 will tend to turn off. If the signal is not heard, the VT1 is in an off state, and the resistor R1 is adjusted, so that the VC1 gradually decreases from the high potential, so that the VT1 enters the enlarged state. Signal sounds can achieve the best effect.
The adjustment of the VT2 static work point is the same as the VT1. Adjusting the resistor R2, allowing the signal to continue to increase by clear, avoiding the signal to harsh. After the adjustment is completed, adjust the potentiometer RP, it will obviously feel that the signal can be large. At this time, the VT2 collector current IC2 is 5 to 10 mA.
It should be noted that when the resistors R1, R2 are adjusted, it is preferable to separate the resistors of the person 1kΩ, 10 kΩ, so as not to remove the resistance to 0 Ω, the power supply voltage will be added to the base and emitter of VT1 and VT2. Between which makes the triode burn down. After completing, the actual impedance is measured with a multimeter, and then the R1 and R2 resistance are fixed.
4. Precautions in use 1, turn on the power supply (the switch with volume control adjustment), the indicator light is illuminated, it can be used.
2. Connect the device crocodile clip and the machine ground, and turn on the power supply to the machine, open the volume switch to the maximum position.
3. Turn the probe from the outputs of each stage. When a certain level is hit, the speaker Y has a signal, indicating that the stage and the stage are normal (the signal refers to the radio broadcast, the tape sound source, or the signal generator).
4, the inspection method is generally starting from the beginning, step-by-step, due to the strength of the final signal, to prevent overload distortion, and can be appropriately reduced.
5. When the measured portion is more than 160V, the corresponding pressure-resistant capacitor should be stronted.
Our other product:
