Bulgarian Makita 125 mm DIY repair

Many are familiar with the situation when a favorite tool stops working for no apparent reason. And if the grinder does not turn on, then, often, the reason for this is a simple breakdown, which can be quickly eliminated without special knowledge and tools. Next, we will consider simple ways to diagnose and repair a power tool using an angle grinder as an example. Initial state - the grinder does not start when the power button is pressed.

To complete the work, we need a multimeter with a dial function and a screwdriver. The first thing to check is the wire, or rather the plug and the place where the wire enters the body. Press the button and "massage" the suspicious areas. Most often, problems arise in the case. If this does not help and the grinder still does not work, go to the next step.

We disassemble the case. To be sure, you can turn on our tester in the dialing mode, and check the integrity of the wires from the plug to the entrance to the button.

Next in the electrical circuit is a button. Often it is the malfunction of this unit that is the reason that the grinder does not start. In order to check this unit, you need to turn it to the ON position, and "ring", as shown in the following photo:

In this case, the button "rang", which indicates its serviceability, so let's move on. This grinder uses a speed regulator, so it is also worth "ringing" it, having previously set it to maximum power.

The next thing to pay attention to if the grinder does not turn on are brushes. In large angle grinders, the brush holders are located outside, in our case - inside the case. We remove the brushes and examine them. It is necessary to make sure the integrity of the contacts on the brush itself. The main criterion for the performance of a brush is its degree of wear or size. In this grinder, it was their wear and tear that caused its failure. Therefore, replacing the grinder brushes will help eliminate the malfunction. For clarity, a comparison is made between new brushes and completely worn out ones.

If, in your case, all this turned out to be serviceable, and the grinder does not work, then the last thing that can be checked without a special tool is the anchor. To begin with, we "ring" between the iron parts of the armature and the collector lamellas. If it rings, then there is a breakdown of the insulation and the armature must be replaced.

Next, you need to measure the resistance between adjacent lamellas on the collector. It should be the same for all pairs. If, at any point of measurement, the resistance is several times higher, then we can talk about a break in the winding. It should be noted that such a malfunction rarely leads to a complete stop of the engine.

If, after carrying out the above diagnostics, it was not possible to identify the malfunction and the grinder does not turn on, then it seems that you will have to contact the master.

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Most of the tools used on the farm are not insured against breakage. The grinders, which almost every master has, fail over time. Different models of angle grinders may have a similar type of malfunction. But each brand has its own characteristics in design and components. The renowned Makita brand is valued for its high quality - durability. However, devices of this brand also tend to break.

Repairs can be done at home. Spare parts for the car can be easily purchased. Before repairing the device, you must familiarize yourself with the attached diagram.

Types of angle grinders of the Makita brand and their features

Based on the diameter of the working wheel, the brand's grinding devices are divided into classes:

• Lightweight - have a circle with a diameter of 115–125 mm. They are distinguished by easy handling.
• Medium - the diameter of the circle is 150–180 mm. There are professional and household models, distinguished by motor power.
• Heavy - disc diameter 230 mm. This class is represented by models for professional purposes when working with concrete, brick, etc. They are characterized by the latest protective systems.

Amateur devices vary in power and price. Professional equipment is designed for long-term heavy loads and has an increased power reserve. Models with power above 1000 W are equipped with a comfortable rear handle, which is covered with special pads to protect against vibration.

As for the design of the grinders of this brand, it is characterized by the presence of such additions:

• labyrinth device, which serves to protect from dirt and dust;
• armored coating of motor windings;
• special system for soft start and overload protection (Super-Joint-System).

Malfunctions when working with Makita angle grinders can be divided into two types:

• electrical (breakdown of the rotor, stator or defects in the control circuit);
• mechanical (breakage of the bearing on the gear wheel).

First you need to inspect the device. The mechanism of operation of the grinder consists in supplying torque from the rotor by means of a gear to the spindle of the working body (circle, cutting stone).

Sources of damage can be increased loads, untimely replacement of brushes, lubricants. Thanks to the presence of a quick-detachable protective casing, Makita models are repaired in a short period of time.

There are components in the control circuit that you can repair yourself. The weak point is the brushes. Therefore, their verification is necessary first of all. And also you should check the continuity of the power supply circuits from the plug to the terminals of the switch.

If the malfunction lies in the breakdown of the switch, then it must be replaced. If the supply wire is damaged and cut, the damaged parts are removed or the entire wire is replaced.

The appearance of an unpleasant odor, constant overheating and spontaneous acceleration of the speed indicate a breakdown of the stator. The stator may have a broken winding or a short circuit. Using a tester or an IK-2 device, you can find a short circuit. In the event of a malfunction, wind up a new wire.

Failure of the stator can be the cause of the breakdown of the angle grinder. This can be understood by the large number of sparks in the collector area and the smell of combustion. The rotor is connected to the gearbox. Therefore, when removing it, it is required to disconnect it from the gearbox. Rotor repair is a complex technology. It will be more practical to replace it with a new part.

The new rotor is placed in the housing already fitted with bearings. And the drive gear is also put on. Then you should check the bearing fit and tighten the nut.

Then the rotor with the gearbox is placed in the stator. In this case, the bearing should be covered with a boot and rotate easily.

If the gearbox is damaged, play in the spindle shaft appears. The gearbox starts to wedge and the gear slips. Gearbox repair is usually associated with damaged gear teeth. For each Makit model, driven gears are attached either to the shaft or pressed onto the spindle. In addition to the driven gear, the gearbox consists of a housing and a driving gear. To repair the angle grinder, you need to replace the gears, and you should replace them in pairs. You will need a puller to remove the driven gear. You can also use a press. It is not recommended to use a hammer due to the fragility of the housing shell.

After troubleshooting the Makita grinder, components are purchased and repairs are made. The following recommendations should be adhered to:

• it is necessary to start assembly by checking the parts for integrity and cleanliness;
• assembly begins with sliding the bearing onto the spindle;
• a driven gear is installed after the bearing;
• the spindle is placed in the gearbox housing using a rubber ring;
• when assembling the gearbox, the bolts are lubricated with sealant;
• when placing the lubricant in the gearbox housing, the volume of its space is taken into account (the volume of the lubricant is 1/3 of the volume of the space);
• at the end of the assembly, the torsion of the gearbox is checked and the bolts for fastening are screwed;
• carbon brushes are replaced after 7 thousand hours of operation or wear up to 8 mm in length.

Makita grinders are very often undergoing a repair procedure due to the high number of counterfeit devices. A frequent problem is the breakdown of the gearbox, namely, its gears.

In addition to the popular Makita brand, other grinding devices of the brands Bosch, Sparky, Stern are known. All of them are reliable and easy to use. But cases of breakdowns are not excluded.

Bosch grinders often require bearing replacement. The mechanism of the machine is based on the torsion of the spindle shaft, which is pressed into the driven gear. And it also rests on a needle bearing. If a bearing breaks down, it is very difficult to get its cage. Moreover, the drive gear is fixed to the rotor shaft with a left-hand thread. As a result, it is fixed with a nut. The gear, which is driven, is pressed onto the spindle shaft.

Reducers of Sparki grinders are characterized by a gear pair placed in a housing. The driven gear is fixed with a press or keyed connection. The key is a small diameter ball. The drive gear is also attached to the rotor shaft with a key or a right-handed nut. The grinders of this model are also distinguished by easy extraction of the brushes without removing the handle.

When disassembling Stern grinders, the gearbox can be left out of the housing. During repairs, pay attention to the key of the small gear, which does not hold well. The lubricant must be changed in a timely manner.

You can and should try to fix any tool. The grinders do not differ much in their mechanism. The diagram is always included with the purchase of the device. Therefore, any craftsman who has the necessary tools and devices can carry out the repair of working units with his own hands.

The grinder, being the most demanded tool in the house, is subject to considerable stress and intensive use. Because of this, after some time, it happens that when the engine is started, jerks, a burning smell and other malfunctions appear, suggesting that the angle grinder (angle grinder) has broken down. But do not immediately carry the device for repair or buy a new one. Most faults in this device can be rectified by yourself.

Over the long years of the existence of such a tool as angle grinder, its appearance, as well as its internal structure, have practically not changed. To repair a grinder with your own hands, you need to know the structure of its mechanical part, as well as electrical.

If you look at the figure below, you can see what parts the angle grinder consists of.

1. Wheel for adjusting the spindle speed of the unit.
2. An electric motor consisting of a rotor and a stator.
3. Start button. Sometimes a soft start system is connected to it.
4. High impact plastic housing.
5. Spindle lock button (used when changing tools).
6. Safety clutch. Protects the motor from overload when the tool is jammed.
7. Protective cover. Covers the tool and protects the user from escaping particles of the processed material, and also prevents injury to a person when a tool is destroyed, such as an abrasive disc.
8. Tool clamping nut. It can be unscrewed using a special key that comes with the power tool. There are also quick-locking nuts that can be unscrewed without a wrench.
9. The gearbox housing and the gearbox itself. Consists of a block of gears that transmit rotational movements from the rotor to the spindle with the tool.

The picture below shows electric diagram of the grinder.

The electrical part of the angle grinder has the following elements:

• electric cable with a plug for connecting to the mains;
• start button;
• stator;
• electric brushes (carbon or graphite);
• collector;
• anchor (rotor).

The following figure shows grinder connection diagram, namely its engine.

All components of an electric motor perform specific functions.

1. Rotor - this is the shaft on which the coils and the collector are located. The rotor, rotating in the magnetic field of the stator, transmits the rotational motion to the angle grinder.
2. Collector... It is the part of the rotor to which all control cables are connected. Electrical signals from the control unit to the engine pass through the manifold. It is to the collector that the electric brushes are connected.
3. Electric brushes. Their main task is to transfer electric current from the power cable to the collector.
4. Stator. It is a coil with a certain number of turns. The task of the stator is to create a magnetic field, which, interacting with the armature, sets the latter in motion.

According to statistics, most cases of failure of angle grinders are associated with the electrical part of the apparatus. Some breakdowns may be minor, which allows you to repair the grinder yourself. But, for example, if the motor windings burn out, only a specialist can repair the angle grinder.

The reasons that the angle grinder does not turn on may be the following:

• defective electrical plug;
• defective electrical cable;
• the start button has broken;
• broken contact between the power cable and the button;
• breakage of the contact wire of the electric brush;
• strong wear of the electric brushes;
• failure of the rotor or stator windings.

There may be different reasons for the angle grinder not picking up speed.

1. Breakage of the speed control unit... To test this version, it is necessary to connect the engine of the device directly, bypassing the regulator, and check the operation of the device.
2. Faulty electrical cable due to constant bending or mechanical damage. Because of this, the damaged wire begins to warm up under load, and the engine speed drops.
3. Dust contamination of the collector... Remove contamination with alcohol.
4. Brush problems... They may wear out or have a short contact wire, as shown in the following photo.

The brush, although half worn out, is quite functional. In this case, the short contact wire prevents the spring from pressing the electrode against the collector. This situation can also be the reason why the angle grinder stopped working in normal mode.

The reasons why the grinder is heating may be as follows.

1. Incorrect mode of operation of the device... As a result of overloads, the electric motor can become very hot, which often leads to burnout of the windings.
2. Bearing failurelocated at anchor. As a result, the rotor clings to the stator, the motor becomes difficult to operate, and the windings overheat. The problem is solved by replacing the bearings.
3. Clogged ventilation ductsthrough which air enters to cool the engine. It is necessary to clean the ventilation openings from dust.

Impeller breakage, which serves to cool the engine. It is installed on the rotor, on the side opposite to the collector. If the impeller is broken, it must be replaced with a new one.

Turn-to-turn closures stator and rotor windings. You will need to rewind the coils or replace these parts with new ones.

If you notice strong sparking when turning on the angle grinder in the place where the collector is located, then the reasons for this trouble may be as follows.

To diagnose the electrical part of the angle grinder, as well as eliminate mechanical damage to the device, you will need to disassemble it. Disassembly is carried out according to the following algorithm.

Using a wrench, remove the disc or other attachment from the spindle of the unit.

Unscrew the handle.

Remove the protective cover.

Open the special windows located on the sides of the casing of the angle grinder, and remove the electric brushes, having previously disconnected the terminals.

Unscrew the gearbox housing from the LBM motor housing.

Pull lightly on the gear housing and detach it from the housing. In this case, the gear unit will be removed together with the rotor.

After removing the armature, the motor stator will remain in the casing, which is also easily removed for diagnostics after unscrewing the fasteners.

To disassemble the gearbox, unscrew the screws holding the cover. Removing the cover reveals the gears of the reducer.

To remove the anchor from the grinder, you will need to unscrew the nut located inside the gearbox.

In order to remove the bearing from the armature, it is recommended to use a special puller. Otherwise, the shaft could be damaged.

As mentioned above, most often the angle grinder refuses to work due to breakdowns in the electrical part of the unit. For the correct diagnosis of the electrical circuits of the instrument, the repairmen of electrical equipment use a special device - tester.

If you pressed the start button of the unit and it does not work, then in 90% of cases the cause of the breakdown is not so serious that you cannot repair the grinder yourself.

Experts advise adhering to the basic rule of repairing a power tool: move from simple to complex.

The first step is to checking electrical cable and plug at its end. If it is collapsible, then unscrew it and check the reliability of the contacts. Otherwise, you will have to disassemble the grinder (remove the cover of the device) and “ring” the cable with a tester, and also make sure that the current goes to the contacts of the “Start” button. If the device shows a break, then the cable should be replaced with a new one.

The situation when the current flows to the button, but does not pass further (when the position is on), indicates switch malfunctions... The button cannot be repaired. It must be replaced with a new one, but first mark the removed contacts in order to connect them correctly in the future. If the contacts are incorrectly connected, the motor winding may burn out.

If during the check it turned out that both the cable and the start button are in good order, but no current flows to the brushes, then it is necessary to make cleaning the contact plates of the brush holders... If this procedure is ineffective, it is recommended to replace the brushes. Further, if everything is fine with the brushes, and the current flows to them, the rotor and stator should be checked for shorts and breaks.

The rotor of the electric motor may have the following faults: interturn short circuit and wire breakage at the contacts of the lamellas. You can check the grinder's anchor with a multimeter: the device is switched to the resistance change mode, the value is set to 200 Ohm, and the resistance between two adjacent lamellas is measured with the help of probes. Thus, it is required to check all pairs of lamellas. If the resistance values ​​are the same, then the rotor winding is not damaged. The detection of other resistance values ​​during the “ringing out”, as well as the detection of an open circuit, indicates a malfunction in this coil. In this case, you will need to repair the grinder's anchor.

Usually, the break of the conductors occurs at the junctions with the winding. Inspect the places where the coils are connected to the lamellas, make sure that the contacts are soldered securely.

If you do not have a measuring device, then you can check the rotor by using 12 V light bulb and battery... The power should be between 30-40 watts. The check is done as follows: apply a voltage of 12 V from the battery to the plug of the angle grinder, connect a light bulb to the break of one wire, start rotating the spindle of the angle grinder. If the winding is in good condition, the light will burn evenly, without blinking. With an inter-turn closure, the degree of incandescence of the spiral of the light bulb will change.In this case, repairing the grinder's anchor with your own hands will be difficult, since the anchor winding scheme is quite complicated, and the process itself requires special equipment and knowledge. Therefore, it is recommended to entrust this operation to specialists. But the best way out of the situation would be to replace the anchor on the grinder with a new one.

If the light does not light up when testing the rotor, this indicates the presence of an open in the stator or a short circuit in its windings, as well as problems with the electric brushes.

To check the stator of the grinder, use, as in the previous case, a multimeter. The values ​​you need set to 20-200 Ohm and do the following. Touch one probe to the contact of the stator winding, and the second to the body of the part. If the device shows resistance, it means that there has been a breakdown to the case. Touch the probes to the contacts of one winding, and then to the contacts of the other. If the resistance is the same, then the coils are serviceable. If the device shows an open circuit on one winding, it means that you will need to rewind the stator or replace the part with a new one.

It will be problematic to rewind the stator at home without special knowledge, skills and equipment. It is better to contact a specialist who is professionally engaged in motor rewinding.