Diagnosis and repair of the Bulgarians with their own hands

Diagnosis and repair of the Bulgarians with their own hands


Angle grinders were made in Bulgaria during the Soviet era. Therefore, the USM also became known as the Bulgarian. At present, there are a lot of firms producing USMs of different models. But the basic elements are the same. Having familiarized yourself with the device, possible breakdowns and diagnostics of the tool, you can carry out repairs of the bulgarian of any modification with your own hands.


  • 1The device and purpose of the Bulgarian
  • 2Basic malfunctions, their causes and diagnostics
    • 2.1How to disassemble and assemble a Bulgarian
    • 2.2Do not untwist the clamping nut
      • 2.2.1How to remove a tightened nut
    • 2.3Do not remove the cover
    • 2.4Check stator
    • 2.5Checking the anchor
    • 2.6Checking the power button
      • 2.6.1How to call the start button
    • 2.7Checking the power cord
    • 2.8Check soft start and speed control
  • 3Precautions before starting repairs
  • 4Troubleshooting with your own hands
    • 4.1Power cord and power button
    • 4.2Soft start and speed controller
    • 4.3Brushes
      • 4.3.1Cleaning brush holders
    • 4.4Stator rewinding
      • 4.4.1Stator rewinding on video
    • 4.5Armature repair
    • 4.6Anchor bearings
    • 4.7Disassembly and repair of the reducer
    • 4.8Spindle lock button
      • 4.8.1Replacing the spindle lock button and repairing the gearbox
  • 5Care and proper exploitation of the Bulgarian

The device and purpose of the Bulgarian

The bulgarian is intended for grinding and cutting of various materials.

The main elements of the Bulgarian

The main elements of the Bulgarian

The Bulgarian consists of the following elements:

  1. A flat case of an aluminum alloy reducer better dissipates heat.
  2. Carbon brushes.
  3. Fastening the handle.
  4. Electronic softstarter. Prevents jerking when turning on and reduces starting loads on the engine.
  5. Quick release protective cover.
  6. Ball bearings.
  7. Electric motor.
  8. Switch Bulgarian.

Basic malfunctions, their causes and diagnostics

Major breakdowns and causes:

  1. Burns, sparks and twitches. Causes: violation of the insulation of the armature winding, wear of the brushes, the collector, clogging of brush holders. Even after replacing the brushes, the Bulgarian will spark and twitch if the brush holders are clogged.
  2. The sound is clapping. Brushes or interturn closure of any of the windings.
  3. A crisp sound. The reason is in the bearings.
  4. Mechanical rumbling and strong tapping. Malfunction of the reducer.
  5. The Bulgarian has stopped working, it does not turn on. If the disc rotates manually or does not rotate, the cause is in the gearbox. If it turns easily, check the electrical circuits. If the chains are working, check the motor and the brushes.
  6. The spindle lock button is broken. The reason is when you press it while the disc is spinning or when the disc is jammed.
  7. Ushm works in fits and starts. Check the motor for intermittent short circuit.
  8. Vibrates. The reason is in mechanics. Check the bearings, rotor shaft and reducer.
  9. It's getting hot. If heated in the area of ​​the engine, then the cause is in worn brushes or short circuits of windings. If the gearbox body is heated, the lubricant has dried or the gears have worn out.
  10. Does not gain momentum or power. The reason is in the electronics or the engine. Check the softstarter control board and the speed controller, brushes and manifold.
  11. Smoke. The reason is overheating of the instrument. Check the motor windings for insulation fusion.
  12. It's buzzing and not spinning. Check the motor bearings and gearbox.

How to disassemble and assemble a Bulgarian

For troubleshooting, the bulgarian must be disassembled.

  • Remove the nut that holds the working disk.
    Mounting the work disk
  • Unscrew the bolts securing the protective cover.

  • Unscrew bolts of the case of the Bulgarian and those with which the body is fixed to the reducer.

  • Remove the upper part of the rear housing. Unscrew the bolts securing the cord. Remove the wires and the button from their slots. In some models, for example, in DWT, the rear housing is not dismantled, but completely removed.

  • Disconnect the motor wires.
  • Remove the brushes.
  • Disconnect the gear housing from the housing of the grinder. Together with it, the anchor of the engine is extracted.
    Anchor with gear
  • Remove the air intake from the housing of the bulgarian.
  • Look inside the housing and you will see two bolts securing the stator to the housing of the bulgarian. Unscrew them.
  • Also there are two contact rings in the form of springs, put on the brush shafts. They are attached to the stator wires. They need to be moved from the mines.
  • To remove the stator from the housing, tap a soft wooden beater against the edges of the housing and the stator will start to exit.
  • Unscrew the gearbox bolts located around the casing attachment.

    Fastening of the reducer housing
  • Remove the reducer.

  • To disconnect the anchor from the aluminum housing, unscrew the nut located in the gear housing.

    Unscrew the nut

Assemble the instrument in the reverse order.

Do not untwist the clamping nut

During operation, the disc can be tightened so tightly with a nut that it begins to crumble. It is not possible to unscrew the nut with a key. And you do not need to do this, because you can break the bulgarian. First, tear the disc to the nut itself. Then find the metal plate a little thinner than the working disk. Use it to drain the remains of the disc under the nut. It can easily be unscrewed with a key or hands. In order not to bring the instrument to this problem, put the washer under the nut.

How to remove a tightened nut

Do not remove the cover

For some Bulgarians, for example, Bosh, the casing is not bolted, but snapped. To remove it, you need to rotate the cutout of the casing perpendicular to the bolgar. To put on, turn to click.


Check stator

The stator is checked by a multimeter.

  1. Interchannel closure. Set the resistance mode to 200 ohms. Connect the instrument probes to the ends of one winding. A unit means a break, and zero means a short circuit between turns. If the resistance shows more than Ohm, then check the second winding. Both windings should have approximately the same resistance.
  2. Breakdown on the mass or short circuit of the winding with the metal housing of the stator. In the multimeter, set the maximum resistance mode. Connect one probe to the end of the winding, the other a stylus with the metal housing of the stator. The unit says there is no breakdown.

Checking the anchor

First visually inspect the manifold and the winding. There may be visible damage: black marks, bent turns of winding, raised, worn or burnt plate collector. After the inspection, proceed to the test by the tester.

  1. Set the resistance to 200 ohms. Connect the instrument probes to two adjacent collector plates. If the resistance is the same between all adjacent plates, then the winding is OK. If the resistance is less than 1 Ohm and very close to zero, there is a short circuit between the turns. If the resistance above the average is two or more times, then there is a break in the turns of the winding.
    Diagnosis of interturn anchor closure
  2. Determination of breakdown on the mass is done in the absence of winding breakage. Place the maximum resistance on the scale of the device. Depending on the tester, it can be from 2 MΩ to 200 PTO. Connect one probe to the shaft and the other to each plate in turn. If there are no faults, the resistance must be zero. Do the same with the rotor. Connect one probe to the iron casing of the rotor and the other to move the plates.

    Determination of the breakdown of the mass of the anchor

Checking the power button

  1. Put the tester into the ringing mode.

  2. Insert one probe into the output of the button, and the other into the opposite input.

  3. Click the button. A beep indicates that this part of the button is working.

  4. Do the same with the other input and output buttons.

How to call the start button

Checking the power cord

Connect one probe to the plug contact, the other to the button inputs. In one of the two positions there should be a beep. Do the same with the other end of the plug.

Check soft start and speed control

If the power button and power cord work, but the engine does not turn on, check the soft start control board. Unscrew the screw that secures the control board. Carefully remove it. Ring all the elements. If the bullet has a speed controller, then it can be connected in series with the power button and have one board with a smooth start. But can have a separate fee. It is tested similarly to a smooth start.

Precautions before starting repairs

  1. Read the instructions. Read the description and the scheme of assembly of the Bulgarian.
  2. Disconnect the tool from the network.
  3. Prepare the workplace on a table with good lighting.
  4. Fix the order of disassembly of the instrument on paper or on the photo in order to collect it correctly after repair.

Troubleshooting with your own hands

If you are unsure of your abilities, then better take the instrument to the workshop.

Power cord and power button

Damaged cord and button must be replaced. On the button, unscrew the mounting bolts of the incoming and outgoing wires. Disconnect it from the chain and put a new one.

Soft start and speed controller


If only the triac is out of order in the control board, then a new one should be put in its place. Pre-grease the metal part of the element with thermal grease. If other elements of the board are burned, then replace it completely.


Brushes should be checked periodically. If one wears by 40% change both. A Also clean the brush holders.

  • To remove the brushes, either remove the rear casing or remove the plugs in the casing.
  • Clean the brush holders from dust and carbon deposits. Wrap the cloth on the screwdriver and moisten with alcohol. Nagar is being cleaned off by the nail file. The brush should easily go in the brush holder, then it will be well pressed with a spring.
  • Insert new brushes.

Cleaning brush holders

Stator rewinding

For high-quality winding of coils you will need an enamel wire and an electrocardboard.

  1. Remove the winding and the old insulation from the housing. Carefully consider the grooves. When the coils burn, insulation is burned and a short circuit to the housing takes place. On it there are naplavleniya, which must be cleaned with nafile or diamond burr. Fusing will interfere with the new winding. It can tear.

  2. The winding is impregnated with varnish. To disconnect the wires and count them, it is necessary to strip out the insulation. Preheat the winding with an industrial hair dryer or any burner.

  3. Burn the fire matches or lighters of any wires, so that the enamel completely burned out. Take the micrometer and measure the thickness. Record the wire diameter and the number of turns.

  4. Take any wire and make a loop from it so that it is placed in the stator grooves. Under the diameter of this loop, pick up some cylinder to wind the turns. For example, a can of aerosol. If its diameter is not enough, then wrap the can with paper.

  5. Wind both windings from the enamel. Fasten the fronts with fiberglass or thick thread. The thread should not break and melt. On the loose ends put on a shrinkable cambric.

  6. From the electrocardboard, make the sleeves and insert them into the grooves. Place the windings in them.

    Rewinded stator
  7. Check the resistance in the windings by the tester. If everything is fine, continue.

  8. To ensure that the wires do not vibrate and do not rub against each other during operation, they must be impregnated with any oil-based varnish. Preheat the starter in the oven vertically and squeeze the lacquer onto the winding with a syringe. When the varnish starts to flow from below, turn the stator and pour it on the other side.

  9. When the varnish dries, proceed to connect the windings. Connect the two ends of the different windings to each other and connect them to the nearest brush. Connect the other two connected ends to the start button. Also connect the wire from the second brush to the button.

Stator rewinding on video

Armature repair

If the balancing is disturbed, the anchor must be replaced. The winding and the collector are subject to repair. Small short circuits are eliminated. If a significant part of the winding is damaged, it can be rewound.

Not strongly developed collector is corrected by a groove. But if the plates are rubbed to the plastic base or partially burned, then the restoration is done by soldering or galvanic build-up.

Severely damaged reservoir

Severely damaged reservoir

If the collector has been completely worn out, after soldering it will last no more than a month of active use. And not until the end of the damaged plate after this repair can withstand several changes of brushes and do not evaporate. You will need to cut the copper plates in size and solder them with a lot of solder. Execute a file and polish.

With galvanic build-up, the recovered copper is very hard. The service life of the collector is like that of a new one.

Fully reconditioned collector

Fully reconditioned collector

Galvanic build-up can be restored as a completely erased collector, and partially damaged plates. The restored collector must be pierced and divided into plates by a drill or a hacksaw blade.

In order to properly rewind the anchor, you need to disassemble it correctly and remove the parameters for the template:

  1. Winding direction.
  2. How many grooves and slats.
  3. Number of conductors in the groove.
  4. The pitch of the winding, that is, how many grooves are between the grooves of one section. For example, if the conductors come out of the first slot and go into the sixth slot, then step = 5.
  5. How many wires enter one slot, as many reels in one section.
  6. Wire thickness.

For example, 80 conductors in the groove, 12 lamellae and 24 grooves. 12 sections of 2 coils. The winding passes in two circles, so we divide 80 conductors in the groove into 2, and 2 more, as 2 coils. We get 20 turns of one coil.

Armature winding scheme

Scheme winding armature
  1. Solder the beginning of the wire to the lamella 1 and pass it through the first and sixth groove. We make 20 turns. The first coil of the first section is ready.
  2. Seal the wire on the lamellae 2 and repeat the winding through the same grooves. The second coil of the first section is ready.
  3. We seal the wire on the lamellae 3. We pass the turn through the second and seventh grooves. We wind the first coil of the second section and seal the wire on the lamellae 4.
  4. The second coil of the second section is fixed to the lamellae 5.
    Scheme of winding the rollers into two circles
  5. Continue so until the end of the wire reaches the lamellae 1
    Finished winding circuit

How to remove an old one and wind a new winding:

  • Hacksaw for metal or wire cutters remove the winding winding parts.

  • Gently, without damaging the grooves, knock out the rods of the remaining parts of the winding with a hammer and a metal chisel.

  • Remove the residue of the impregnation with the nail file. Count the conductors in the groove and measure the diameter of the wire. Draw a diagram. Cut the liners from the cardboard for insulation and insert them into the grooves.

  • After winding, weld the sections' conclusions to the collector plates. Check the winding with a tester.

    Winding sections
  • Saturate the winding with epoxy resin.

Anchor bearings

Bearings eventually crumble or jam. They need to be changed.

  • Disassemble the Bulgarian, remove the anchor from the stator.
  • Anchor is inserted into the gearbox housing by bearing. If the housing is not removed, fix the rotor in a vice and tap the wooden bar along the gearbox housing.
    Removing the armature from the gearbox housing
  • Remove the pinion from the armature shaft.
  • There are two bearings on the armature shaft. The one next to the collector is removed easily. The second bearing remove the puller. If it's not there, hang the anchor behind the bearing and tap it on the shaft with a piece of wood. The hammer can not be used.
    How to remove the bearing
  • Push the new bearing on the collector end onto the shaft. Place the second bearing in the gear housing from the side of the rotor. Insert the pinion inside the housing and tap the nut so that it enters the grooves of the gear. Insert the armature into the gear housing. Tighten the nut.

Disassembly and repair of the reducer

The reducer must be disassembled not only for repair, but also for preventive cleaning and lubrication.

  • Unscrew the bolts and disassemble the gearbox housing. You will see dirty grease, which must be removed.
    Dirty grease in the gear housing
  • To check the bearings, shake the gear shaft. He should not hang out.
  • Remove the circlip from the shaft, nut and pinion.
  • Hang the shaft by the body and with a wooden pin, gently tap on the shaft to remove it.
  • Remove the circlip from the housing that holds the bearing.
  • With the help of a spacer, for example, an end head, knock out the bearing from the housing.
    Disassembled gearbox
  • If necessary, replace the bearing and gear.
  • To insert the bearing into the body, select the size of the prefix and tap it carefully.
    Bearing in gear housing
  • To clean the gearbox, warm up the cabinet with a hairdryer and
    Pure reducer

    the old grease will pour out of it. Clean the parts with a rag or toilet paper. Rinse the case and parts with kerosene.

  • Apply new grease recommended by the manufacturer in the instructions to the tool.
    Gearbox after cleaning and lubrication

Spindle lock button

If the button has flown out, then it is impossible to work with such a Bulgarian.

Spindle lock button

Spindle lock button

Since the spindle can spontaneously drop onto the gear and lock it during operation.

Spindle lock block

The block of fixation of a spindle in the disassembled kind

The fixing unit consists of a spindle with a rubber ring, a spring and a plastic button.

  1. To replace the button, disassemble the gearbox.
  2. Remove the spindle from the housing.
  3. Put the spring on the button on the inside.
  4. Insert the spindle into the gear housing from the inside, and the button from the outside. Press until you hear a click.
  5. Assemble the reducer.

Replacing the spindle lock button and repairing the gearbox

Care and proper exploitation of the Bulgarian

To work for Bulgarians for a long time, follow the rules:

  1. Watch for the integrity of the wire insulation, plugs. Do not remove the protection.
  2. Lubricate and clean the entire tool.

  3. Regularly check the wear of the brushes and contamination of the brush holders.
  4. Do not overheat the tool.
  5. Do not drop it.
  6. After turning off the Bulgarian, wait for the circle to stop rotating, then put it on the ground. When the engine stops, the tool through the vents sucks in the air flow particles and other hard fractions that hit the engine windings. The result is an open or short circuit.

  7. Try not to use the bulgarian in the winter season on the street. While you are working, the engine heats up. The air is icy. As a result, condensation forms. Moisture to the engine is fatal.
  8. Always place the circles recommended by the tool manufacturer. If the bulge is 180 mm, do not put more than 200 mm there. The larger the circle, the less should be the speed. You will have to remove the protection, and the revolutions will be exceeded. Vibration and vibration will increase. As a result, the circle will break apart. This is fraught with not only serious injuries. The bearing of the gearbox breaks down, the gears are erased.

If you actively use the Bulgarian, then you are a good master. To understand the device of the instrument and fix it with your own hands will not be difficult for you. First find the fault and determine which nodes should be checked. Repair the Bulgarian carefully, without haste, so that the minor breakdown does not turn into a large one.

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