A maintenance tool
Multimeter two ( each a simulation and digital , analog indispensable ) , diagonal pliers, needle nose pliers , soldering iron, iron frame . Flux, solder wire , solder suckers , fine sandpaper , heat shrink tubing , wire stripper , flathead screwdriver ( small each one ) , Phillips screwdriver ( small each one , plus a rubber handle screwdriver ) , art knives.
Second, the circuit works
1 , the process
Input ( protection, micro switch ) → → Filter → pros and cons of switching rectifier → Motor → Clutch
2, the normal parameters of the electronic components
( 1 ) , Power cord: measuring DC resistance , normal close to zero ; common faults: open circuit or poor contact ( break ) .
( 2 ) , micro switch : measuring normally open ( resistance approaches infinity ) and normally closed ( resistance approaching zero ) between the resistance value ; common faults: Contact poor ( blackened ) , the keys can not properly reset the body rupture.
( 3 ) , protector: measured resistance value ; normally zero ; mild overload can after the Auto- reset is too large to be permanently disabled . It can also be disconnected when the temperature ( thermal protection ) , at room temperature could also be automatically reset.
( 4 ) , rectifier bridge: the output terminal ( + , - ) short-circuit , the measured output ( + , - ) DC resistance (15K or so ) .
( 5 ) , positive and negative switch: toggle keys corresponding pin is common pin , toggle keys corresponding to the two tranches connected.
Third, the circuit detection and analysis
When unexplained failure to get an electric screwdriver , you should first make a preliminary test , as follows:
The multimeter dial to (× 1K) files zeroing open ( press ) micro switch , the measured input DC resistance , is the case for the 15K or so ( digital multimeter to read at the diode test , showing a pressure drop of 1.0 left ) , this value can be part of the work described electric screwdriver circuit to work properly, another detection circuit approach is the electric screwdriver open, shorted motor poles , under normal circumstances , the measured resistance is slightly less than the DC input terminal of the initial test most value ( motor not included in the calculation DC resistance ) .
Fourth, the component parts of the motor
1, the basic components: an armature (rotor ) , brush holder , the motor front cover , bearings , magnets (stator ) , brush , motor gasket.
( 1 ) , the armature : electric screwdriver, the most important parts , such as the "heart ", as the state will determine the armature power granted can not work properly. The quality of the armature : We can measure the DC resistance of its known. Under normal circumstances , the armature commutator DC resistance between adjacent poles (220V) is 15 ohms or so ( because different manufacturers , its value is not the same , the larger than 20 ohms DC resistance ) .
Damage characteristics and failure analysis : A, to judge from the appearance of visible signs of the armature commutator wear, wear more serious armature its work big noise : B to see whether the central axis of the armature becomes smaller ( fitted with bearings after bearings can sloshing around ) is obvious , the armature center of rotation instability, noise as well. C, there are many open-circuit armature poles due to adjacent commutator can not work properly . When there are multiple disconnected, the motor does not start ; when there is a disconnect motors can work, but if the contact is just brush off place, the motor will stop working.
( 2 ) , carbon brush holder: from the appearance of judge without damage and internal carbonized ( charred ) .
( 3 ) , the motor front cover : judge from the appearance that they have broken.
( 4 ) , the stator : judge from the appearance of its internal disk for damage and shifting element ( resulting magnetic asymmetry ) , but can also be placed inside the magnet slotted screwdriver size test its magnetic , magnetism is too small, should be replaced new magnets.
( 5 ) , bearing : to judge from the rotational bearing stuck phenomenon , and its strong sense of internal friction , the motor cry noisy .
( 6 ) , Brush : Brush wear to the remaining twenty-three mm , the replacement of carbon brushes ( regular replacement ) .
( 7 ) , gasket : a fixed armature , to prevent shaking up and down , to ensure stability . Appropriate number of shims ; armature not shaking up and down , you can twist the armature with a smaller force .
Fifth, the clutch
A clutch common faults: ( 1 ) . Not stuck Screwdriver : A drive shaft bad, replace the drive shaft ( ball trough becomes large ball off automatically ) ; ( 2 ) . Lack of ball , make up the new ball .
2 , the drive shaft damage : ( a ) . Appearance of severe wear on head screwdriver , replace ; ( 2 ) . Internal fault ( test method is to put fan clutch , and then stuck with screwdriver twist shaft, escape a sense of judgment , and to determine its quality . )