Currently, the market is saturated with chainsaws of foreign and domestic production, differing in appearance, size, power, but all of them are united by one main detail - gasoline engines.
The ignition of the fuel-air mixture in the combustion chamber of the engine in the previous domestic engines of chainsaws was carried out by a spark obtained from the magneto, which was subsequently replaced by manufacturers with an electronic ignition unit for the chainsaw (MB-1 and MB-2).
There are situations when the chainsaw fails to work precisely because of the inoperative electronic ignition unit.
How can you be sure of this? How to find the cause and eliminate it?
You can disassemble the ignition unit in parts and poke around in them, comparing them with serviceable ones, or you can assemble a simple device that will help determine the malfunction in the electronic ignition unit of the chainsaw in a couple of minutes.
How to make a device for checking the ignition block of a chainsaw.
We have assembled a device that can accurately determine the working or non-working ignition unit of the chainsaw.
Checking the electronic ignition of a chainsaw The device consists of a horseshoe-shaped core assembled from a package of strips Electronic ignition of a chainsaw transformer steel, with a pulse coil and an excitation coil located on it.
The excitation coil (named after our definitions) is designed to excite an alternating magnetic field, into which the tested electronic ignition unit of the chainsaw is placed.
The impulse coil (also named according to our definitions) energizes the electronic switching system (signal coil), that is, the electronic switch.
Chainsaw Electronic Ignition Testing
The coils themselves are checked with an ohmmeter (tester) and energized.
An ohmmeter is used to check the compliance of the ohmic resistance of the winding of the coils specified by the manufacturer.
Charging coil ≈ 3.26kΩ.
High voltage coil:
1. From the coil body to the high-voltage terminal ≈ 1.4kΩ.
2. From the coil body to the capacitor terminal ≈ 1Ω.
Signal (commutation control) coil ≈ 69Ω.
In case of an obvious discrepancy between the resistance (usually reduced), one should think about burning through the insulation of the winding wire and its internal short circuit.
Lack of resistance indicates a break in the winding.
The volt-storage capacitor is checked by a tester or changed to a known good one.
You can check separately each coil of the ignition unit without removing it from the unit itself or separately removed.
The core of the coil under test should be located in the gap between the ends of the core of the device.
The charging coil of the ignition unit in the magnetic field of the device produces an alternating voltage of the order of 80v - 100 v.
The signal coil of the ignition unit (controls electronic ignition switching) produces 5.5v-6.7 (6.2) v.
With a high-voltage coil, the situation is different, because it has three connecting points in the circuit: a high-voltage terminal, a terminal to the case, and an input from a capacitor.
Between the high voltage terminal and the terminal to the case, the voltage will be about 50v-60v.
Between the terminal to the case and the terminal to the capacitor - 0.4v-0.8v.
Between the high voltage terminal and the capacitor terminal - 47v-52v.
The monolithic electronic ignition unit can also be checked with our device, but such a unit cannot be repaired due to the type of execution. You can only determine whether the unit is working properly or not.
Well, if a spark discharge was not observed when checking the electronic ignition, then the likely reason for this will be a malfunction of the electronic ignition switching circuit.
To assemble our electronic ignition circuit, we used the following elements:
VD-KU201 (instead of BT136);
D1-EM516;
R1-27om (KF4-3);
C1-0.25-0.5μF (630v).
D2-IN4007 (LD). When using the KU-201 thyristor, the D2 element is not needed.
Circuit-ignition-chainsaws The entire assembly is located in the box body of the block instead of the old one.
The thyristor is shortened in the threaded part (anode). The cathode contact is also slightly shortened.
After setting up and checking the unit on the device, the entire assembly is filled with silicone to protect it from moisture, dust and vibration.
The proposed circuit can be assembled by any beginner or person who is fond of electrical engineering. It contains a minimum of elements and is easy to assemble.
With your own hands
Repair
In the arsenal of necessary tools, many summer residents have a chainsaw. It is an irreplaceable assistant when cutting and pruning trees, when preparing firewood for the winter, during construction, and generally a useful tool for a good owner. Unfortunately, the chainsaw sometimes breaks down and has to be repaired.
Of course, if you have a new chainsaw and it still has a warranty, then there is only one solution - to carry the saw to the service, where they will make warranty repairs. When the warranty period has expired, repairs in the service will already be paid. In this case, if you have at least some kind of skill in working with equipment, it makes sense to try repairing a chainsaw with your own hands. In addition, the chainsaw is not such a complicated mechanism as it seems at first glance, and the cause of the malfunction is sometimes very simple.
So what if your chainsaw won't start? First of all, of course, you need to check the presence of fuel - gasoline in the tank. If there is fuel, we find the spark plug on the saw engine, unscrew it and see what state it is in - if there is carbon deposits, if the spark plug is filled with fuel. If the candle was filled with gasoline, then wipe it dry and additionally dry the combustion chamber of the cylinder. To do this, turn off the fuel supply and operate the starter several times. After that, we screw in the candle and try to start. When examining a candle, you should pay attention to the gap between the electrodes - (0.5 - 0.65) mm. Then we check for a spark. To do this, we put the high-voltage wire on the candle, with pliers with insulated handles, press the candle body to the cylinder and pull the starter. If there is a spark, everything is fine, if not, the ignition system is faulty. Both the high-voltage wire itself and the ignition module may be faulty. Defective parts must be replaced.
Another very common cause of chainsaw malfunction is the fuel system. It is enough to disconnect the fuel supply hose from the carburetor - if gasoline comes in, then everything is fine. If there is no gasoline or it just drips, then the probable cause is a clogged filter or breather. The filter is replaced with a new one, the breather is cleaned with a needle. Remember to change the fuel filter every 3 months of saw operation. The carburetor can also be misaligned or clogged. It must be regulated strictly according to the instructions after rinsing and cleaning.
The air filter is checked, as a rule, it is very dirty. The filter is washed in water with detergent, then dried and put back in place.
The muffler of the chainsaw is cleaned of dirt and combustion products, as this can cause the saw to stall under load. More serious problems with the engine itself, with pistons, already require more serious repairs. Clean your chainsaw regularly, change filters, do not overload and it will serve you for a long time and trouble-free.
Features of the ignition of a chainsaw
Check-of-performance-electronic-ignition-chainsaw
The principle is as follows: the tested ignition unit of the chainsaw is placed near the ends of the horseshoe-shaped core, and a high-voltage discharge is checked at the output of the high-voltage coil.
At the tested block MB-1 and MB-2, the output from the impulse (signal) coil is soldered off (in some cases, this may not be done if its resistance corresponds to the reference one).
The block is positioned near the ends of the device so that the charging coil core is located in the gap between the ends of the horseshoe-shaped core.
One end of the wire from the impulse coil of the device is connected to the metal case of the ignition unit, the other end to the tap located at the signal coil of the electronic unit.
An external conductor (high-voltage wire) with a spark plug installed on it is connected to the output of the high-voltage ignition coil.
The body of the candle is connected to the body of the tested electronic unit. Instead of a candle, you can use a high-voltage spark gap with an adjustable gap or a conventional break from the high-voltage wire to the electronic ignition unit housing.
The device is connected to an AC mains.
If the electronic switching unit is in good working order, then a discharge will be observed at the place of the high-voltage gap (spark gap) or spark plug, if the high-voltage coil is in good working order.
How to adjust a chainsaw
When buying a chainsaw, the shop assistant will check the tool with you. However, this does not mean that she is ready to go. Already before the first start, you will have to make certain settings and check the main components of the saw. Therefore, it is extremely important to know how to adjust your chainsaw so that it will serve you trouble-free for many years.
To make the adjustment correctly, it is necessary to become familiar with the basic elements and construction of the saw. The instruction manual supplied with the instrument is sufficient for this. Chainsaw adjustment consists of the following steps:
- chain tension adjustment;
- carburetor adjustment;
- idle speed adjustment;
- ignition adjustment.
To adjust the chain tension, loosen the clutch cover nuts and turn the adjusting screw until the chain is in the desired state, that is, it should not chat too much, but also should not be overtightened.
The chainsaw carburetor has been adjusted at the factory. Therefore, it is not recommended to change anything in its settings. If you are not satisfied with his work, then it is better to immediately, while the chainsaw is still under warranty, contact the service center. The same goes for ignition.
Idling at the first start needs not so much adjustment as it needs to be checked. To do it, turn the idle speed adjustment screw clockwise until it stops, and then counterclockwise 4.5 turns. If the engine then runs without rotating the chain, then everything is in order. Otherwise, we go to the service center. It is dangerous to work with such a saw!
In different models of chainsaws, the settings may differ slightly. However, the basic principles of saw tuning remain the same for all manufacturers of this tool.
Specifications
Chainsaw electronic ignition unit
Despite the wide distribution of imported chainsaws, the population, especially in rural areas, still uses many domestic Druzhba and Ural devices. Both saws have a common drawback that I also had to face - the fragility of the electronic ignition unit. This problem is not new - see the article by P. Ivanov "Repair of the ignition unit of a chainsaw" in "Radio", 2003, No. 2, p. 45. Currently, it is not difficult to buy a block, but it is expensive and does not last long. I decided to start developing my own design, which I bring to your attention.
Unlike the one mentioned above, the ignition block does not contain external elements and fits entirely into the original dimensions of the factory block. The old block board must be removed.
The block diagram is shown in Fig. 1. Generator coil L1, ignition coil (high-voltage transformer) T1, capacitor C1, inductive ignition pulse sensor L2 and duralumin base are used from the old ignition unit. The rest of the elements are newly introduced.
Rice. 1 Schematic diagram of the device
When the flywheel rotates, the generator coil L1 generates an alternating current, which, after rectification by the diode bridge VD1-VD4, charges the capacitor C1. At a certain position of the flywheel, a short pulse of positive polarity appears at the terminals of the L2 sensor coil, which, having passed through the VD5 diode and the current-limiting resistor R1, opens the VS1 SCR. Capacitor C1 is discharged through the open SCR and the primary winding of the ignition coil T1. Its secondary winding generates a high voltage pulse, which is then fed to the spark plug.
On transistor VT1, resistor R2 and Zener diode VD6, an opening pulse amplitude limiter is assembled. As long as the voltage at the control electrode of the trinistor VS1 does not exceed the stabilization voltage of the Zener diode VD6, the transistor VT1 is closed and does not affect the control electrode circuit. When the zener diode VD6 is opened, current begins to flow through it and the resistor R2. A voltage arises across the resistor R2, which slightly opens the transistor VT1, which bypasses the control electrode circuit of the VS1 trinistor. As a result, the amplitude of the pulse is limited to about 4 V with the zener diode indicated in the diagram. This voltage is enough to confidently open the SCR.
In order for the described design to fit into the dimensions of the factory ignition unit, it is necessary to modify the trinistor. To reduce its length, the threaded shank was shortened (1-2 threads were left), the cathode and control leads were also shortened to a length of 4 ... 5 mm. Before shortening the terminal, it must be squeezed in two places near the body with side cutters with blunt cutting edges. Then, above these places, the output is bitten off and the cut is soldered with solder.
You can compress the terminal no closer than 2 mm from the SCR housing, otherwise the insulator will crack. This compression is needed to increase the contact area between the inner conductor coming from the crystal and the outer terminal of the SCR.
Installation of the unit is carried out with a rigid copper wire with a diameter of 0.4-0.45 mm in vinyl insulation. Diodes VD1 - VD4 are assembled close to the block and their leads are soldered in such a way that on one side of the block you get AC leads, and on the other - DC. The transistor is secured with a screw that secured the factory board. A petal is placed under the transistor, to which the leads connected to the case are soldered. Resistors, diode VD5 and zener diode VD6 are soldered on the terminals of the transistor VT1 by hinged mounting.
The capacitor C1 is placed in the same place, the VD1-VD4 bridge is placed in the same compartment. The wires from the L1 coil to the bridge are flexible, of the same cross-section. The wire going to the SCR anode is soldered to its body. Before filling with the compound, the SCR is held "suspended" on rigid wires in such a way that it does not protrude beyond the dimensions of the unit, and a gap of about 2 mm remains between the SCR case and the duralumin base of the generator. The assembled block, after checking for operability, is poured with epoxy compound, making sure that the parts of all elements close to the edges and the trinistor body are covered with a layer of compound. After the compound has hardened, the SCR is rigidly fixed to the generator base. The finished block is shown in Fig. 2.
Rice. 2 View of the finished block
When installing the unit in a chainsaw, it may be necessary to adjust the ignition timing. In practice, more often it was necessary to set earlier relative to the factory mark. If you plan to install the unit in the Ural chainsaw, before assembling you need to remove the part of the landing protrusion from the back side of the base, painted in Fig. 3 in blue, flush with the base plane. Under the remaining parts of the protrusion, when installing the block in place, it is advisable to put gaskets made of heat-insulating material, for example, asbestos cardboard, no more than 0.5 mm thick. With a thicker flywheel, it is possible that it will touch the parts of the block. Gaskets are needed because the design of the Ural chainsaw provides for the installation of an electronic ignition unit directly on the wall of the engine crankcase, which heats up very much during prolonged operation.
Rice. 3 Reverse side of the part
In the above block, instead of those indicated in the diagram, you can use the KD105G, KD209 diodes with any letter index, as well as others suitable in size with a reverse voltage of at least 400 V and an average forward current of at least 0.3 A. 147, KS 156 with letter indices A, B, G, or their imported counterparts, provided that the sum of the stabilization voltage of the Zener diode VD6 and the voltage IBE of the transistor VT1 does not exceed the permissible voltage at the control output of the SCR. Trinistor KU202N can be replaced with KU202M, KU205V, KU205G. Trinistors in a plastic case should not be used due to their insufficient resistance to overheating.
In conclusion, I will add that according to the description presented, more than 20 blocks were assembled and they work for a long time and reliably. The block I assembled and installed 6 years ago on my chainsaw has never failed
CHAINSAW OPERATING PRINCIPLE
The main question that buyers ask themselves is the simplest: how to buy the right product? But even little-known brands have dozens of instrument names on sale, not to mention world-famous companies. How to choose the right one? To do this, it is worth figuring out what the main characteristics of the chainsaw mean, why they are highlighted and whether large numbers always mean high performance, and not just high cost.
Technical parameters are directly related to the design of the tool and the principle of its operation. For example, the power and the permissible dimensions of the saw headset depend on the volume and type of the motor. The weight depends on the design and the materials used.
In general, the design of a chainsaw is a motor, torque transmission mechanisms and a saw blade. A gearbox (transmission system) and a clutch system are connected between the engine and the chain. The saw blade is a bar with a chain placed on it. Since the engine of the chainsaw is two-stroke, it has 2 tanks - oil (for chain lubrication) and fuel (for the fuel mixture).
A fuel mixture is used, not gasoline, due to the structure of the two-stroke engine, which does not have a separate tank for lubricating its internal elements.
The tool works as follows: when the user pulls the starter "cord" - the crankshaft spins. In the event that there is a sufficient amount of fuel mixture in the tank, then at one of the revolutions the spark plug is triggered - the spark ignites the mixture. When it burns, it releases gases that increase in volume, which push the piston. This element is connected through a connecting rod to the crankshaft, which by inertia goes to the second revolution, thereby continuing the process anew without the participation of external forces. When starting the saw, the motor starts to spin the drive sprocket. A saw blade is attached to it, and the chain, driven by an asterisk, begins to "walk" in the grooves of the tire. Lubrication of the chain occurs automatically when driving - at the end of work, after switching off the chainsaw, you will notice that a certain amount of lubricating oil comes out of it - this is unused oil remaining in the grooves.
Specifications
Volumes of the engine, fuel tank and oil tank
The size and capacity of the engine directly affect the power of the saw itself, the larger it is, the more energy is released for the movement of the piston. The volume also indicates how much fuel the saw is using in a given amount of time. It should be borne in mind that if the volume of the engine does not match the power of the saw, this reduces its service life, due to the inefficiency of use.
The volume of the tank for the fuel mixture ranges from 0.3 to 1 liter. Accordingly, the oil tank is 1.5-2 times smaller. This difference in volumes helps to consume the fuel mixture and oil at almost the same rate (about 30-50 minutes) at full load on the tool.
For household saws, the engine volume reaches 40 cc, which is 1.5-2 hours without refueling. Semi-professional saws, capable of working for 8 hours, have an engine with a volume of up to 60 cc, and professional ones up to 121 cc. Models with a large volume are additionally equipped with starting aids.
Power
The larger the engine displacement, the more powerful the saw, and, therefore, more productive. The speed and intensity of the cut depend on the power. This indicator is measured in "horsepower" or in kW (1hp = 0.735 kW). Depending on the power, the saws are divided into classes and areas of application.
Up to 2 kW - household
0.74 to 2.94 kW - semi-professional
2.94 to 5.15-6 kW - professional
Chainsaws with high power require additional physical effort during operation and knowledge of safe use techniques, since it is quite difficult to operate such a tool. The power of the equipment can be reduced due to natural wear of components, the use of a poor-quality fuel mixture and an incorrectly selected saw headset.
The weight
Nominally, the weight of the saw is the sum of the weight of the motor and body with handles. Knowing the weight, you can also get an idea of the functional accessories of the equipment:
Household saws weigh an average of 2 to 5 kg. They do not need a lot of power and the main requirement for them is the convenience and simplicity of performing periodic small works (harvesting firewood, cutting branches).
Semi-professional saws weigh a little more - 5-7 kg, which indicates a higher power, and, accordingly, an expansion of the work front. Since this type of saw is often used as a delimber, lightweight tires are provided.
As for professional saws, the weight of the most powerful of them can reach 11 kg. They are "lighter" due to the use of lighter alloys (mainly based on magnesium) for the production of the cylinder and crankcase. The goal is to make the tool lighter, but not to reduce the service life, reliability and safety during the operation of the product.
In fact, when using a chainsaw, the master not only experiences the load of these elements, but also the weight of the saw headset, fully filled fuel and oil tanks. Therefore, if a small mass is an important criterion, it is worth giving preference to household and one-handed saws - they are lighter than others. This parameter becomes decisive when choosing a tool for crown cutting - cutting off the upper branches and throughout the crown of the tree. In this case, a heavy chainsaw is not only ineffective, but also dangerous - the maneuverability is low, and the mass and vibration of a powerful engine will quickly lead to fatigue of the master, it is difficult to hold it in weight and it is completely impossible to do it with one hand. Therefore, for this type of work, a specialized, lightweight tool is recommended.
It should also be borne in mind that people who are contraindicated in intense physical activity are not recommended to use chainsaws weighing more than 5 kg.
To work with a professional tool, you need good physical fitness, because for safety reasons such saws are not provided with a belt attachment due to the high risk in case of unforeseen complications in the work (falling of a tree, for example). The operator must have time to release the tool, and not free from it.
The serrated bumper makes it easy to operate on professional saws. It is located on the body next to the saw bar, so when this element rests against the tree trunk, it is easier to hold the saw - it is no longer suspended.
Bus length
The bar is one of the main parts of the saw. It is a support for the chain and a channel for its lubrication (due to the movement of the chain shanks in the grooves during operation).
An important characteristic of a tire is its length. It is she who determines the maximum thickness of the trunk that the tool can cut. The longer the bar, the deeper the cutting depth.
As a rule, all manufacturers indicate the maximum bar length in the characteristics of the saw. If, however, a tire larger than the permissible one is installed on a compact saw, then due to a lack of power, the movement of the chain along it will be an additional load for the engine. This will wear out the entire saw head much faster and increase fuel consumption.
Chainsaws with short and standard (30-40 cm) tires are more often found in the household class, and for professional ones, lengths from 45 cm to 1 meter are possible. It should also be borne in mind that with an increase in the length of the tire, the recoil force increases with the resistance of the material.
Chain pitch
The saw chain is part of the saw unit. Consists of riveted links (teeth). Its parameters are chain pitch, profile height, drive link thickness and cutting depth. Among them, the main one is the chain pitch - this is the distance between three consecutive rivets on the chain, divided by 2.
The chains are divided into five groups, depending on the step size:
14 inches (6.35 mm)
Miniature chains rarely used in Russia. They are mounted on low-power single-handed saws.
0.325 inches (8.25 mm) and 38 inches (9.3 mm)
Low profile chains come with this step. More than 80% of the saws produced worldwide are equipped with such chains. Also, they are the safest for inexperienced users due to the low probability of kickback and low vibration during operation.
0.404 inches (10.26 mm) and 34 inches (19.05 mm)
This step is the hallmark of a high performance chain with coarse links. These chains are used on harvester equipment and heavy duty felling saws. A large step, due to this, and a larger layer, removed in one pass, but, accordingly, the resistance of the processed material is also greater.
Additional properties
Anti-vibration system
First of all, the use of such a system is necessary on professional models of chainsaws, because Long-term work with a powerful vibrating instrument has a rather detrimental effect on the joints and can lead to serious consequences.
Its simplest form is a set of rubber gaskets located between the handles and the body. However, such an anti-vibration system is practically not used in modern chainsaws. As a rule, the principle of "two masses" is implemented: the engine block is separated from the handle block and the fuel tank.
Dependence of the impacts of the chain elements on the material: less step - less layer removed in one pass, respectively, and the resistance of wood is also less. As a result, the vibration level naturally decreases.
In the absence of a normal anti-vibration system in the instrument, several years of work with it can lead to sad consequences, ranging from poor circulation in the hands and ending with more serious diseases. However, some household chainsaws are not equipped with an anti-vibration system. Its absence is explained, firstly, by the short duration of the use of tools, and secondly, by the fact that they do not develop high power and chains on them with a smaller step.
Cutting speed
When purchasing a chainsaw, buyers often ask a question about the speed of cutting wood with a specific example of a chain saw (for example, whether it is necessary to "press" on the entire tool when working). We answer: first of all, it depends on the condition of the saw headset and, in particular, the chain. When working with a blunt chain, not only will the sawing efficiency be low, but the likelihood of saw failure increases, as the load on the engine increases. Therefore, for professional use, it is recommended to regularly "edit" the chain (for example, at the end of the working day). In addition, the shape of the cutting tooth and the chain pitch make a significant contribution to productivity.
Some manufacturers indicate the cutting speed in the product passport. However, it is always necessary to remember that such data are very arbitrary, since it is impossible to calculate all the cut options with the resistance of all available materials. But there is no doubt that by informing us about such indicators, the manufacturer thereby assumes responsibility for the level of equipment operation. And, knowing the cutting speed, you can count on your chainsaw to be able to do this without compromising its integrity.
Installing the air filter
The point of having an air filter in chainsaws is that it keeps dust, sawdust and other small particles from getting into the engine and chassis. The protection system in this case is two-part: the first barrier will be the impeller, fixed on the motor shaft, and the next - the air filter itself, nylon or felt. This element retains most contaminants and is easy to clean or replace during maintenance. It can also be impregnated with special oils that increase the trapping coefficient of microparticles and prevent them from "cementing".
Chain brake
This function is a direct necessity, proceeding from the peculiarities of the chainsaw operation: in the event of a "kickback" or accidental breakage of the chain, irreparable harm can be caused to the operator. Therefore, the best solution in this case is to stop the chain. It occurs through a mechanism that is activated by the chainsaw flap. If the sawer's hand rests against it, then by means of the lever the force is transferred to the brake and the chain is blocked. This can happen automatically.
Repair of the ignition block of the Ural (Druzhba) chainsaw
L1 - generator coil, d = 0.063mm, W = 11000 turns, R = 3000 ohm; L2 - control coil, d = 0.1mm, W = 1200 turns, R = 80 ohm; T1 - high-voltage transformer, d1 = 0, 28mm, W1 = 75 turns, R1 = 0.5 ohm, d 2 = 0.063mm, W2 = 6900 turns, R2 = 2000 ohm; E - electronic unit; C1 - capacitor 0.47 μF 630V; R1 - 390 ohm resistor 0 , 25 W; V1 – V5 - diodes, correspond to КД 209; V6 - thyristor corresponds to КУ 202
Before starting the repair, it is necessary to determine by what scheme the ignition unit is assembled.
Option one. It is necessary to measure the resistance of the generator coil L1 and the secondary winding of the transformer T1, the resistance of the control coil L2 and the primary winding of the transformer T1, it is not necessary to measure, it is enough to check them for an open circuit. Then check the serviceability of the thyristor control circuit by measuring the resistance. We connect one probe to the sealed terminal going to the resistor R1, the second to ground. In one direction, the resistance should be equal to the sum of the resistances of the resistor and the direct transition of the diode V5 approximately 2 - 4 kΩ. In the other ∞. If all the windings and the thyristor control circuit are in good working order, it is necessary to drill, with a diameter of 1.5-3 mm, at the junction point of the anode of the thyristor V6 with the capacitor C1 (point A), and after soldering the coils, check the diodes V1-V4 for serviceability, and the capacitor C1. If one of the diodes is faulty, it can be soldered by a hinged mounting, having previously destroyed the old faulty diode using the drilling method. It is better to use a drill for this purpose.
In the event of a malfunction of the capacitor C1, it must be removed, a new one must be inserted and the terminal must be soldered to the indicated point, then it must be poured back with epoxy glue.
In the event of a thyristor malfunction, I recommend replacing the block circuit completely, first removing the old one, soldering it with a hinged mounting and filling it with epoxy glue.
 | Additionally, if the resistance of the thyristor control circuit is greater than the norm, the contact of the circuit with the ground may be broken, to restore it is necessary: to release the M3 bolt from the glue, unscrew it, clean the contact and tighten it again, but already a new one (point B), or simply solder the suspended conductor by connecting it to the magneto body. |
N. Tukmachev
Announcement!
A semiautomatic machine for winding generator coils magneto MB-1 is on sale. Inexpensive.
Now, in shops for land works, you can buy any equipment, but many on farms use walk-behind tractors and motor-cultivators from the times of stagnation.
Other owners have been using Mole walk-behind tractors for 20 years and suddenly a breakdown - the MB-1 electronic ignition unit has failed.
The main disadvantage of the MB-1 electronic unit is its miniaturization and circuit flaw,
Although there is a proven option with light motorcycles and mopeds - a generator coil, electronic filling and an ignition coil - there are no separate components and problems in the ignition system.
And in MB-1, the winding of the generator coil is made with very thin wiring and the ignition coil is small, and most importantly, the electronic part of the circuit is located on the engine crankcase and heats up to 80 degrees. And the KU202N thyristor used in the circuit is designed for 75 degrees. Therefore, permanent malfunctions. The same thyristors were used in the ignition circuits found on light motorcycles and mopeds and worked reliably. The thin winding wire of the generator coil does not allow generating more current and setting the storage capacitor to 1 μF.
Try to blow these ignition elements apart. I will give an example of how the familiar from the forum improved the ignition unit.
Found a car ignition coil. An electronic circuit is mounted in the body of the burned-out switch.
The ignition coil was mounted on the steering wheel plate of the walk-behind tractor.
From the original MB-1 unit, the generator coil and the sensor coil remained, in place from the native ignition coil I installed a second generator coil,
you just need to fit the seat under it.
A flywheel with four magnets is installed on the walk-behind tractor, one of them is inverted so as not to be wise with phrasing of the windings - each generator coil with its own diode bridge.
After all alterations - multiple ignition reliability. Thyristor T 122-25-8 military model, diode bridge for a thousand volts, eternal ignition coil.
Ignition wiring diagram:
The figure on the right is the connection of the generator coils. They are connected at points A B in the left diagram.
Diode bridge - RC207.
Capacitor C 1 - 1 μF.
Thyristor - 10 amperes and 800 volts. I put - T 122-25-8. 25 A 800 V.
Diode VD1 - type HER308, fast action.
Diode VD2- 1N4007.
Resistor R1- within 2 kOhm.
The best part is that starting a walk-behind tractor is a pleasure.
A device for checking the ignition block of a chainsaw.
Currently, the market is saturated with chainsaws of foreign and domestic production, differing in appearance, size, power, but all of them are united by one main detail - gasoline engines.
The ignition of the fuel-air mixture in the combustion chamber of the engine in previous domestic chainsaw engines was carried out by a spark obtained from a magneto, which was subsequently replaced by manufacturers with chainsaw electronic ignition unit(MB-1 and MB-2).
There are situations when the chainsaw fails to work precisely because of the inoperative electronic ignition unit.
How can you be sure of this? How to find the cause and eliminate it?
You can disassemble the ignition unit in parts and poke around in them, comparing them with serviceable ones, or you can assemble a simple device that will help determine the malfunction in the electronic ignition unit of the chainsaw in a couple of minutes.
How to make a device for checking the ignition block of a chainsaw.
We have assembled a device that can accurately determine the working or non-working ignition unit of the chainsaw. 
The device consists of a horseshoe-shaped core assembled from a pack of strips 
transformer steel, with pulse coils and excitation coils located on it.
The excitation coil (named after our definitions) is designed to excite an alternating magnetic field, into which the tested electronic ignition unit of the chainsaw is placed.
The impulse coil (also named according to our definitions) energizes the electronic switching system (signal coil), that is, the electronic switch.
Technique for determining a malfunction of the ignition of a chainsaw by the device.
The principle is as follows: the tested ignition unit of the chainsaw is placed near the ends of the horseshoe-shaped core, and a high-voltage discharge is checked at the output of the high-voltage coil.
At the tested block MB-1 and MB-2, the output from the impulse (signal) coil is soldered off (in some cases, this may not be done if its resistance corresponds to the reference one).
- The block is positioned near the ends of the device so that the charging coil core is located in the gap between the ends of the horseshoe-shaped core.
- One end of the wire from the impulse coil of the device is connected to the metal case of the ignition unit, the other end to the tap located at the signal coil of the electronic unit.
- An external conductor (high-voltage wire) with a spark plug installed on it is connected to the output of the high-voltage ignition coil.
- The body of the candle is connected to the body of the tested electronic unit. Instead of a candle, you can use a high-voltage spark gap with an adjustable gap or a conventional break from the high-voltage wire to the electronic ignition unit housing.
- The device is connected to an AC mains.
- If the electronic switching unit is in good working order, then a discharge will be observed at the place of the high-voltage gap (spark gap) or spark plug, if the high-voltage coil is in good working order.
The coils themselves are checked with an ohmmeter (tester) and energized.
An ohmmeter is used to check the compliance of the ohmic resistance of the winding of the coils specified by the manufacturer.
- Charging coil ≈ 3.26kΩ.
- High voltage coil:
1. From the coil body to the high-voltage terminal ≈ 1.4k Ω.
2. From the coil body to the capacitor terminal ≈ 1Ω.
- Signal (commutation control) coil ≈ 69Ω.
In case of an obvious discrepancy between the resistance (usually reduced), one should think about burning through the insulation of the winding wire and its internal short circuit.
Lack of resistance indicates a break in the winding.
The volt-storage capacitor is checked by a tester or changed to a known good one.
You can check separately each coil of the ignition unit without removing it from the unit itself or separately removed.
The core of the coil under test should be located in the gap between the ends of the core of the device.
- The charging coil of the ignition unit in the magnetic field of the device produces an alternating voltage of the order of 80v - 100 v.
- The signal coil of the ignition unit (controls electronic ignition switching) produces 5.5v-6.7 (6.2) v.
With a high-voltage coil, the situation is different, because it has three connecting points in the circuit: a high-voltage terminal, a terminal to the case, and an input from a capacitor.
- Between the high voltage terminal and the terminal to the case, the voltage will be about 50v-60v.
- Between the terminal to the case and the terminal to the capacitor - 0.4v-0.8v.
- Between the high voltage terminal and the capacitor terminal - 47v-52v.
The monolithic electronic ignition unit can also be checked with our device, but such a unit cannot be repaired due to the type of execution. You can only determine whether the unit is working properly or not.
Well, if a spark discharge was not observed when checking the electronic ignition, then the likely reason for this will be a malfunction of the electronic ignition switching circuit, its repair is simple for those who are at least a little familiar with the soldering iron.
