How to repair an electric screwdriver if it is broken? Now let me share with you some points to pay attention to during maintenance.
1、 Repair tools
Two multimeters (one analog and one digital, indispensable for analog type), diagonal pliers, pointed pliers, soldering iron, soldering iron holder. Flux, solder wire, tin absorber, fine sandpaper, heat shrink tubing, wire stripping pliers, flathead screwdriver (one small and one medium), Phillips screwdriver (one small and one medium, plus a rubber handle screwdriver), art knife.
2、 Circuit working principle
- Process
Input (protector, micro switch) → rectification → filtering → forward/reverse switch → motor → clutch - Normal parameters of each electronic component
(1) Power cord: Measure the DC resistance value, and the normal value tends to zero; Common faults: Open circuit or poor contact (breakage).
(2) Micro switch: measure the resistance value between normally open (resistance approaching infinity) and normally closed (resistance approaching zero); Common faults: Poor contact of contacts (burnt black), inability to reset buttons properly, and body rupture.
(3) Protector: measure resistance value; Normal is zero; After mild overload, it can automatically reset, but when it is too large, it will permanently fail. It can also be disconnected in case of high temperature (thermal protector), and can automatically reset at room temperature.
(4) Rectifying bridge: Short circuit the output terminal (+, -) and measure the DC resistance (around 15K) of the output terminal (+, -).
(5) Positive and negative switches: The pin corresponding to the toggle key is a common pin, and the two gears corresponding to the toggle key are connected.
3、 Circuit detection and analysis
After receiving an electric batch with an unknown cause of malfunction, preliminary testing should be conducted first, as follows:
Set the multimeter to the (× 1K) position to zero, turn on (press) the micro switch, and measure the DC resistance at the input end. Under normal conditions, it is about 15K (the digital multimeter is adjusted to the measuring diode and displays a voltage drop of about 1.0). This value indicates that the electric batch circuit is working properly. Another method to detect the circuit is to turn on the electric batch and short-circuit the two poles of the motor. Under normal circumstances, the measured DC resistance at the input end is slightly lower than the initial measured value (the DC resistance value of the motor is not included in the calculation).
4、 Components of a motor - Basic components: armature (rotor), carbon brush holder, motor front cover, bearings, magnet (stator), carbon brush, motor gasket.
(1) Armature: The most important component of an electric batch, like the “heart”, the state of the armature will determine whether the electric batch can work properly. The quality of the armature can be determined by measuring its DC resistance. Under normal circumstances, the DC resistance (220V) between adjacent poles of the armature commutator is about 15 ohms (due to different manufacturers, the value may vary, with larger DC resistances exceeding 20 ohms).
Damage characteristics and fault analysis: A. Judging from the appearance, whether the commutator of the armature has obvious wear. Armature with severe wear produces loud noise during operation. B. Check whether the central axis of the armature has become smaller (after installing the bearing, the bearing can shake left and right). If it is obvious, the rotation center of the armature is unstable and the noise is also loud. C， Many armatures cannot function properly due to open circuits between adjacent poles of the commutator. When there are multiple disconnections, the motor cannot start; When there is a disconnection, the motor can work, but if the carbon brush happens to be in contact with the disconnection, the motor will stop working.
(2) Carbon brush holder: Judging from its appearance, whether it is damaged or internally carbonized (burnt black).
(3) Motor front cover: Judging from its appearance, it is damaged.
(4) Stator: Judging from its appearance, whether there is any damage or displacement element in the internal disk (causing magnetic asymmetry). At the same time, a screwdriver can be placed inside the magnet to check the size of its magnetism. If the magnetism is too small, a new magnet should be replaced.
(5) Bearing: Judging from the phenomenon of jamming by rotating the bearing, when the internal friction is strong, the motor noise is loud.
(6) Carbon brush: When the carbon brush wears down to two or three millimeters, replace it with a new one (regularly).
(7) Gasket: Fix the armature to prevent it from shaking up and down, ensuring stability. Appropriate number of gaskets; The armature will not sway up and down, and can be twisted with less force.
5、 Clutch - Common clutch faults:
(1) Unable to hold screwdriver head: A drive shaft is broken, replace drive shaft (steel ball groove becomes larger, steel ball automatically falls off);
(2) Missing steel balls, add new ones. - Damaged transmission shaft:
(1) The screwdriver head is severely worn on the appearance and needs to be replaced;
(2) Internal fracture: The testing method is to install the fan blade into the clutch, then lock it in place, twist the transmission shaft with a straight screwdriver, judge the jumping sensation, and determine its quality.
