Common faults and maintenance of electronic calculators

　　1. The display is dim or bright and dim after booting

　　First, measure whether the voltage of the battery used is normal. If it is normal, you can further check whether the battery spring pressure is sufficient and whether the contact is good. If there is any problem, you can stretch the spring sheet or use fine sand to polish the contact points of the battery pole pieces.

　　Two, there is a digital display after booting, but it can't be calculated

　　Use a multimeter to check the circuit board to see if there is a short circuit between the terminals of the integrated circuit block. Use a multimeter to check the voltage value of the keyboard input terminal of the integrated block (24~29 pins for L1-3033E chip). The normal value should be about 0.12V, otherwise it may be possible. The manifold is broken. If the voltage is normal, but the operation cannot be performed, it may be that the keyboard is in poor contact, the circuit board has foreign objects, the circuit board is open, or the keys are stuck.

　　Three, no display failure

　　First of all, check whether there is any problem with the battery . Because the button battery is easy to flow out of lye to corrode the battery contacts, it should be cleaned up during maintenance;

　　Secondly, it is necessary to carefully check the circuit board for wireless head oxidation or even disconnection, and whether the copper foil of the circuit is broken. If so, it can be soldered with a well-grounded soldering iron;

　　Once again, remove the calculator battery, set the multimeter to R×1 or R×10, connect the black test lead of the multimeter to the positive terminal of the battery, and connect the red test lead of the multimeter to the negative terminal of the battery. At this time, the multimeter has a slight deflection, indicating the circuit Basically normal. If the pointer of the multimeter is not deflected, the circuit is not connected. The pointer deflection of the multimeter is close to 0, indicating that there is a short circuit in the circuit, which needs to be carefully searched and eliminated. The pointer deflection of the multimeter is slightly larger. If it is not for the high power consumption of the microprocessor itself (genuine products generally do not have high power consumption), it is due to the increased distributed capacitance of the circuit board. At this time, you need to remove the circuit board, scrub it with absorbent cotton dipped in absolute alcohol two or three times, and then irradiate it with an incandescent lamp for 1-2 hours before assembling it. The conductive rubber and the part where the LCD screen touches the conductive rubber can also be baked together after being lightly wiped with an alcohol cotton ball. Large distributed capacitance is a common cause of no display and power consumption.

　　The circuit board is fully inspected and repaired, and then the LCD screen is inspected: use one end of a wire to wind the lamp line or other AC power line that has been plugged in for 1 to 2 times, and the other end is exposed a little core, and the core is placed on the LCD Slowly flick the part where the screen touches the conductive rubber, and each stroke will appear. If it does not display, the LCD screen is broken. Some strokes are not visible or very light. Generally, the access wire of the stroke is broken (the access wire is a thin layer of light blue, which can be observed, and the wires connected to each stroke inside the LCD screen can also be clearly seen) .

　　Four, lack of strokes

　　In addition to the breakage of the LCD screen access wire checked above, it may also be caused by poor contact of the conductive rubber or the wrong position of the LCD screen.

　　If the connecting wire of the LCD screen is not broken at the root, you can adjust the conductive rubber to press it on the root. If the effect is not obvious, you can use soft and thin facial tissues to cut into small strips with a width of nearly 1mm, and soak in carbon ink (carbon has Conductivity), after a little drying (with certain humidity), stick it on the corresponding broken wire (not touch the adjacent wire), and then let it dry naturally. If the root is broken, you can fold the upper carbon paper in several layers, and then cut into small pieces to fill in the right angle of the root. During assembly, the conductive rubber is used to press the carbon paper to connect the wires. The paper cannot be stacked too high or too wide, so as not to affect adjacent strokes. It is also possible to use cotton thread soaked in carbon ink instead of facial tissues, and the selection is flexible and convenient depending on the operation.

　　If the LCD screen has been disconnected, you can use "sticky" or other adhesives to fit the LCD screen completely and paste it on the aluminum window under the LCD screen, and then use the method described above to repair it. After the root fracture is repaired, the strokes are slightly lighter, but it can be used normally. After assembling, if the strokes are incomplete, you can try to press the conductive rubber part of the circuit board by hand. If the strokes appear to be complete, it is because the fixing screws are not tightened or flattened. If the hand pressure does not change, you can loosen the screw and move the LCD screen left and right. The above methods can be used in combination to assemble the calculator and make the strokes appear complete.

　　Five, the buttons do not work

　　The reason is that there is dirt between the conductive rubber of the button and the circuit board, or the conductive power of the rubber has deteriorated. The maintenance of the former only needs to be cleaned with alcohol and then installed. For repairs where the conductivity of the rubber has deteriorated, use scissors to cut the water-absorbent and wear-resistant newspaper into small pieces, then glue it to the rubber contacts, and then apply carbon ink on it, and then repaint it after drying. , And install it after drying. If you have a TV cable, you can take out the metal foil inside to replace the paper (no more carbon ink), the effect is better.

　　Maintenance precautions

　　There are field-effect elements in the calculator, which can also be damaged by a slightly higher AC induction current. Take precautions during soldering and baking. The baking temperature should not exceed 45℃; when repairing a broken LCD screen, be careful to soak the carbon ink paper along the broken cracks of the LCD screen and cause joint writing. , It can be soaked and wiped with an alcohol cotton ball; the surface of the LCD screen (the side where the characters are displayed) should not be wiped with alcohol; so as not to be dissolved by alcohol. Do not soak or wipe the conductive rubber effect with alcohol for a long time. Although there are some differences in the performance and grades of various calculators, the structure is basically the same, and the maintenance methods are basically the same.

　　Commonly used repair methods for calculators

　　1. Washing and drying

　　Cleaning is like the oil of a mechanical watch. It is an indispensable repair method for a calculator. Through cleaning and drying, various dysfunctions caused by dirt and moisture on the anvil can be eliminated, and the service life of the calculator can be prolonged at the same time.

　　2. Counterpoint and reinstall

　　Misplacement and looseness are often the common causes of various malfunctions of calculators. Through the steps of alignment and reassembly, the positions of the LCD screen, the conductive rod and the printed circuit board can be adjusted to restore the normal display.

　　3. Derusting and shaping

　　Metal components are prone to oxidation, corrosion, insufficient elasticity and deformation, etc. During the repair process, rust removal, cleaning and shaping must be performed to ensure reliable contact and electrical conductivity between the components.

　　4. Change the battery

　　Inferior quality and exhausted batteries are also common causes of malfunctions in calculators. Such malfunctions can be restored to normal operation as long as they are replaced with new batteries.

　　5. Repair printed circuit boards

　　The printed circuit board of the calculator is made of copper plate. It is often affected by high temperature and humidity, and the insulation performance is deteriorated. After repairing the board, most of them can return to normal.