General faults and maintenance methods for electronic scale weighing displays:
Understand the basic structural principle of the electronic weighing instrument, if there is some basic knowledge of electronic circuits (will look at the circuit diagram), we can carry out the maintenance of the electronic weighing display. Whether it is repairing instruments or other electronic products, there are generally two kinds of ideas. One is a circuit for judging a problem with a fault phenomenon. This is a commonly used method and is often effective. If it is a more complicated circuit, this method will often cause misunderstanding, but the result will be half the effort. At this time we need to calm down and use the second method - the investigation method. The investigation method is to check one by one according to the normal detection means, and finally find the problem. The steps of the troubleshooting method are as follows:
(1) First check the power supply. The power supply is the main stimulus for the entire circuit. Before checking the circuit, we must first check if the power supply is normal.
(2) Next, check the input part, which is the small signal amplification part. Connect the signal input to the signal source, adjust the input size of the signal source, and see if the voltage after amplification is regular.
(3) Check if the processor is working. Use an oscilloscope to test whether the crystal oscillator is oscillating and test whether the output of each point is normal.
(4) Check the drive circuit and other output circuits.
In the maintenance process, we use the combination of visual inspection, component elimination, and confirmation maintenance to complete our maintenance work. As long as we have confirmed which part of the circuit is faulty or damaged, we can proceed to the next step to solve the problem. After these steps, you can basically find out where the problem lies. Here are some common faults and solutions for electronic weighing displays:
(1) Failure analysis that cannot return to zero after the weighing object is removed Check whether the sensor output signal value is within the standard (A/D total amplification code / use inner code range / bottom code range), if the signal value is not in the standard Inside, adjust the sensor adjustable resistance, adjust the signal value to the standard. If it can't compensate, please check if the sensor has any problem. When the sensor output is normal (the scale body is stable), lock the instrument fault, generally the amplifier circuit and A/ D conversion circuit has a problem, and then judge the test analysis one by one according to the circuit principle, in order to finally solve the problem.
(2) Failure analysis of inaccurate weighing Whether the internal code value is stable, whether there is friction in all parts of the sensor, whether the power supply is stable, and whether the operational amplifier circuit is normal, use the weight to test whether the weighing of the weighing pan is average. Further instrumental analysis or weight correction according to the instructions.
(3) Failure to start up First determine the problem of non-fuse, power switch, power line and voltage switch, check the transformer for AC voltage input and AC output. If the meter has a battery, remove the battery and turn it on with AC power to see if it is caused by insufficient battery voltage. Secondly, check whether the rectifier circuit, the voltage regulator circuit, and the display driver circuit are abnormal. If there is no problem, check whether the processor and the auxiliary circuit are burnt out.
(4) Display garbled The original display circuit is removed and replaced with a normal display circuit to see if it is normal. If the display is normal, the display circuit has a problem. If it is not normal, check the drive circuit for faults. Finally, check if the processor shows that the output pin is in a reasonable output range.
(5) The button is not easy to use. Replace the new button for testing. If the new button function is normal, it can be judged that the button is in poor contact, and the circuit between the button and the CPU is disconnected or soldered. Check the button holder for poor contact. Measure whether there is a short circuit or open circuit between the button and the diode, resistor, etc. on the CPU circuit.
(6) It is not possible to say that full load and non-return to zero are possible, and most of them may change due to the small signal input range. According to the method that cannot be returned to zero, if the problem cannot be found, first check whether the power supply and A/D circuit are normal, and then detect the sensor output.
(7) Sensor fault discrimination method 1 Static measurement method: use the ohmmeter of the universal meter to measure the E+ of the sensor to S+, S- (or E- to S+, S-) or not, In general, the compensation needs to be compensated when the error is above 0.5Ω. If the error is too large (more than 2Ω), it is recommended to replace the sensor.
2 Dynamic measurement method: Connect the sensor wiring correctly to the motherboard, and use the digital V-meter of the digital meter (more than four and a half) to measure whether the voltage of S+ to ground and S-ground is equal (preferably 0 error), if not equal, sensor compensation is required.
(8) Sensor compensation If the sensor output signal is too high, add a resistor to make the signal value to the normal range between the sensor's “E+S-†(the lower the resistance value, the lower the sensor output signal).
The sensor output signal is too low or - ERR Please add a resistor to make the signal value to the normal range between the sensor's "E+~S+" (the lower the resistance value, the higher the sensor output signal).
The method of detecting the A/D circuit amplification code applies the electronic scale to the internal setting state (to display the current internal code state), and applies the full weighing weight to record the amplified code value. Their relationship: bottom code value + full Weigh the amplification code + safety zone code.
(9) Failure analysis of digital instruments The maintenance of digital instruments is relatively simple. It only needs to detect the power supply circuit, communication circuit, CPU micro-processing circuit, storage circuit and display circuit. According to the instructions of the manual, different error phenomena and actual The measurement results are resolved by problem. The premise is to ensure the performance of the digital sensor is normal.
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