How to repair imported electric screwdriver
First, the repair tools
To perform effective repairs, you'll need a variety of essential tools. These include two multimeters—one for analog and one for digital (the analog one is particularly important), diagonal pliers, needle-nosed pliers, a soldering iron with a stand, flux, solder wire, desoldering pump, fine sandpaper, heat shrink tubing, a wire stripper, small and medium-sized flathead screwdrivers, small and medium-sized Phillips screwdrivers (including one with a rubber handle), and an art knife. Having these tools on hand ensures you can handle most common electrical and mechanical issues.
Second, the working principle of the circuit
The basic process of the circuit is as follows: Input (from a protector or micro switch) → Rectification → Filtering → Positive/Negative Switch → Motor → Clutch. Understanding how each component functions is crucial for diagnosing and fixing problems.
Here are the normal parameters for key components:
(1) Power line: Measure the DC resistance. A normal value should be close to zero. Common faults include open circuits or poor contact.
(2) Micro switch: Check the resistance between normally open (which should be close to infinity) and normally closed (close to zero). Faults may involve burned contacts, failure to reset, or physical damage.
(3) Protector: The resistance should read zero under normal conditions. It can reset automatically after slight overload, but will permanently disable if overloads are severe. Some protectors also disconnect due to high temperature and reset once cooled down.
(4) Rectifier bridge: Test the DC resistance between the positive and negative output terminals, which should be around 15K ohms.
(5) Positive/Negative switch: The pin connected to the toggle switch is the common terminal, while the other two positions correspond to the different settings.
Third, circuit testing and analysis
When dealing with an electric tool that has an unknown fault, start with a preliminary test. Set your multimeter to ×1K and measure the DC resistance at the input by pressing the micro switch. If the reading is around 15K (or about 1.0V on a digital multimeter in diode mode), it indicates the circuit is functioning properly. Another method involves shorting the motor after opening the tool. Normally, the input DC resistance should be slightly lower than the initial value, excluding the motor’s own resistance.
Fourth, the components of the motor
A typical motor consists of several parts, including the armature (rotor), carbon brush holder, front cover, bearings, stator magnet, carbon brushes, and a gasket. Each plays a critical role in the motor's performance.
(1) Armature: This is the core part of the motor, often referred to as its "heart." Its condition directly affects whether the motor operates correctly. You can assess the armature by measuring its DC resistance. Under normal conditions, the resistance between adjacent commutator segments should be approximately 15 ohms (varies by manufacturer; values above 20 ohms may indicate issues).
Damage signs include visible wear on the commutator, excessive noise during operation, or a misaligned central axis causing instability. Open circuits in the commutator can prevent the motor from starting or cause it to stop when the carbon brush contacts a break.
(2) Carbon brush holder: Inspect for physical damage or internal discoloration (blackening).
(3) Motor front cover: Look for cracks or deformations.
(4) Stator: Check for internal damage or displacement that could affect magnetic symmetry. Use a screwdriver inside the magnet to test the magnetic strength—weak magnets should be replaced.
(5) Bearings: Listen for unusual noises or resistance when rotating. Stiff or noisy bearings can cause the motor to run roughly.
(6) Carbon brushes: Replace them when they wear down to about 2–3 mm in height, and do so regularly to maintain performance.
(7) Gasket: Ensures the armature remains stable. Too few or too many shims can cause the armature to wobble or rotate unevenly.
Fifth, clutch
Common clutch problems include:
(1) Inability to engage the screwdriver head: This could be due to a broken drive shaft, which needs replacement. If the slot is worn or the shaft falls off automatically, it must be replaced.
(2) Missing parts: Replacements should be made as needed.
Damage to the drive shaft can occur due to heavy wear on the tip or internal breaks. To test, insert the fan into the clutch and snap it. Then use a screwdriver to twist the drive shaft and feel for any irregularity or lack of resistance—this can help determine if it's damaged.
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