How to correct the digital multimeter's inaccurate current, voltage, and resistance readings
According to my maintenance experience. First you need to make sure your multimeter battery voltage is normal, 9V battery voltage, if the battery voltage is normal, check the A/D reference voltage. Generally it is 100mV, if the A/D reference voltage deviates from 100mV, it will appear If the measurement error becomes larger, you can adjust the calibration reference voltage through the vR1 variable resistor to perform calibration. The A/D model of the DT9205A digital meter is ICL7106. The 32 pins and 36 pins of the 7106 are the reference point presser foot detection points. The vR1 variable resistor can also calibrate the DC voltage measurement value. The capacitance file adjustment calibration is calibrated through the VR3 variable resistor adjustment.
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The actual model number of 1AM is MMBT3904. This is an NPN transistor without adding resistance to the B pole. So after using this model, the actual resistance difference is about 10K. MMBT3906LT1G-2AM
Is your multimeter damaged by using the wrong gear? If the function is still normal, you can consider removing the buzzer. Without it, the repair of the digital multimeter is more troublesome.
These meters are the lowest-end three-and-a-half-digit multimeters, and they all use the A/D conversion chip made of ICL7106A. .
It can be found directly on a certain treasure, but generally the chips are rarely broken, and most of these bullshit chips are broken and have no repair value. .
The working voltage of the chip is not normal, but it does not mean the problem of the chip itself. It is very likely that the operational amplifier in the peripheral circuit is damaged and the working voltage of the chip is pulled down, causing the current of the whole machine to become high, which causes the multimeter to work abnormally. It is possible. It is recommended After troubleshooting the peripheral faults, check the chip itself.
