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First, measure the voltage of pin 6 of the preamplifier module 5 G23 to ground, and adjust the zero adjustment knob. If it can be changed around ±0 mV, it means no problem with the preamplifier. Then, measure the output voltage waveform of the comparator of the A/D converter. The waveform of this point should be a square wave. When using a multimeter to measure this point, if the pointer does not swing and the display number is large, it indicates that the circuit before this point has a fault. Measure the voltage waveform of pin 6 of the preamplifier integrated block 5G23. This point should be a sawtooth wave. The pointer should be swung largely during measurement. If you use a multimeter to measure this point, the pointer does not swing, and the display number is large, indicating that the 5G23 integrated block of the preamplifier is damaged, replace the 5G23, and the instrument is normal.
Five Common Problems and Maintenance of Digital Acid Meter
The digital pH meter is a 4-digit decimal precision digital display pH meter, which inputs the potential generated by the electrode in the measured solution to the A/D converter through the preamplifier, showing the pH of the solution. The following describes the common faults and troubleshooting methods of this instrument.
Digital pH meter adjustment zero knob, the instrument can not be zero, but the number can change.
Under normal circumstances, use a multimeter to measure the ground voltage of the instrument's preamplifier 5G23 pin 6 and adjust the zero adjustment knob. The voltage at this point should be adjustable at ±0 mV, if not ±0 mV, indicates that the circuit before this point is faulty. Measure the source-to-ground voltages of the two insulated gate FETs G1 and G2, and adjust the zero adjustment knob. The two points should be adjusted to equal ground voltage and the voltage to ground should be ±0 mV. If the voltages measured at these two points are not equal, it means that the two insulated gate FETs are not paired and the two paired FETs must be replaced. Measure the voltage of the foot of the preamplifier integrated block 5G23 on the ground. If the zero adjustment knob is adjustable to within ±200 mV, and there is no matching FET on the market, emergency measures can be taken and two field effects can be taken. The resistance of the tube source is increased or decreased to test, and the preamplifier should be capable of integrating the voltage of pin 6 of pin 5G23 to ground.
Adjustable around ±0 mV.
Digital pH meter mV block can not be zeroed
mV block zero drift
Use a multimeter to measure the voltage of pin 6 of preamplifier 5G23 and adjust the zero adjustment knob at the same time. It is found that the zero point voltage is the same as the instrument display number, indicating that the circuit is unstable before this point. Measure the source-to-ground voltages of the two insulated gate FETs G1 and G2. Observe that the voltage at this point also drifts. This indicates that the insulated gate FET is unstable. After replacing the two paired insulated gate FETs, The instrument is normal.
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When the mV block is pressed and the digital pH meter is input with a voltage value, the instrument displays a negative value and the measured voltage value is normal regardless of whether the input voltage is positive or negative.
After analysis, the preamplifier of the digital pH meter , A/D converter, and the driving circuit for displaying the value are all normal, and the positive and negative driving circuit is in failure. Use a multimeter to measure the voltage of the positive and negative integrated circuit 5G601 pin 17 to record the voltage value, then input the positive and negative voltages respectively at the input end of the instrument, and observe whether the point potential is reversed. As a result, it was found that there was no change in the point potential, indicating that the driver 5G601 was damaged, and the 5G601 was replaced, and the instrument returned to normal.
The highest digit is displayed as zero, and the remaining digits are all displayed, but not digitized.
Use an oscilloscope to check the counts of the four input terminals A, B, C, and D of the frequency division circuit block 5G657 and the l7th terminal that is advanced to the high position.