A semi-automatic welding machine is an electrical apparatus designed for the welding process using an electrode.
Structurally, the semi-automatic welding machine is equipped with electronics with high frequencies. The latter has the property not only to increase the performance of the units, but also often show its "capricious" character.
The repair procedure for an inverter semi-automatic welding machine (the model and manufacturer have no influence) begins with a typical opening of the machine and inspecting the internal parts. It is possible that already during the initial inspection it will be possible to identify a part that has become unusable.
If no external changes are observed, then they are taken for diagnosis.
Scheme of the device of the welding semiautomatic device.
First, check the fuses on the control board. Using a tester or an ohmmeter, a broken element is calculated by dismantling the board. Having found it, it is carefully changed to a new one and the semiautomatic device is reassembled. With all starters in working condition, they look for the problem further, analyzing possible circuit problems.
Often, the repair of a semi-automatic welding machine is associated with malfunctions of field-effect transistors, which are the weakest point. Signs of malfunctions (they were mentioned above) outwardly do not manifest themselves in this group of elements at all. It is extremely rare for the case to crack and the leads to melt. These features make it necessary to search for burnt transistors by calling them one by one with a multimeter.
Another moment of diagnosis is the control of the components of the driver responsible for the operation of field-effect transistors. Worn-out elements can be determined with an ohmmeter.
Scheme of the welding rectifier.
Please note: in order not to be confused, both the driver elements and the transistors are recommended to ring in relation to the circuit of the existing inverter semiautomatic device, having chosen the direction in advance (for example, from top to bottom). In this case, the risk of not taking into account or missing any element will be reduced to zero.
If the fault is still not found, the diagnosis is completed by checking the main elements of the rectifiers (or diode bridges).The latter are the most reliable parts of an inverter welding machine and fail infrequently, however, it is not advisable to completely discount the likelihood of their failure. To diagnose the diodes located on the radiators, they are unsoldered from the board. A working diode changes resistance from plus to minus and vice versa. With other test results, the diodes are thrown away.
Repair of a semiautomatic device in case of detection of malfunctions described above comes down to replacing failed components.
Overheating is often the cause of transistor failure. In the case of checking the inside of the unit, it would be useful, just in case, to change the thermal paste at the points of contact with the heat sink plate.
And in the event of a breakdown, you can take a look at the contacts. Those that don't seem very tidy are cleaned and joined.
Do-it-yourself repair of a semi-automatic welding machine is a rather favorite process among craftsmen who often perform body work.
Scheme of a welding transformer.
But it is not always possible. Although with a minor breakdown, an attempt to search for it may not be meaningless.
One of the problems that do not require mandatory professional intervention is sticking of the electrode when the current strength is selected correctly. The causes of breakdowns are the following factors:
If the welding arc is unstable or the wire used is not completely melted, the contact tip may have become unusable or the ground clamp is connected incorrectly. To get rid of the inconvenience in the work, the tip is replaced and the clamp area is cleaned of dirt.
Failures in the shielding gas supply, resulting in poor weld quality, can be caused by gas diffuser failures. The problem is solved by replacing the element.
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So, most of the problems are eliminated by the option of changing quickly wearing elements of the welding machine. When all actions do not help, they resort to the help of a service center that has at its disposal the required technical base for repairing welding machines.
The weakest element of welding transformers is the terminal block to which the welding cables are connected. A bad contact, together with a high welding current, leads to a strong heating of the connection and the wires connected to it. As a result, the connection itself is destroyed, the insulation at the ends of the windings burns out, as a result of which a short circuit occurs.
Repair of the welding transformer in this case comes down to sorting out the heating joint, cleaning the contact surfaces and clamping them to ensure tight contact of all elements.
Among others, the following malfunctions occur.
Spontaneous shutdown of the welding machine . When the transformer is connected to the network, its protection is triggered, as a result of which the device is turned off. This may be due to short circuits in the high voltage circuit - between the wires and the case or the wires between themselves. A short circuit between the turns of the coils or sheets of the magnetic circuit, as well as a breakdown of capacitors, can also lead to the operation of the protection. When repairing, it is necessary to disconnect the transformer from the network, find the defective place and eliminate the malfunction - restore the insulation, replace the capacitor, etc.
Strong transformer hum often accompanied by overheating. The reason may be the loosening of the bolts tightening the sheet elements of the magnetic circuit, a malfunction in the fastening of the core or the mechanism for moving the coils, an overload of the transformer (excessively long operation,high value of welding current, large electrode diameter). A short circuit between the welding cables or sheets of the magnetic circuit also leads to a strong hum. It is necessary to check and tighten all screws and bolts, eliminate violations in the mechanisms for attaching the core and moving the coils, check and restore the insulation in the welding cables.
Excessive heating of the welding machine . The most common reasons for this include a violation of the operating rules in the form of setting the welding current above the permissible value, using a large diameter electrode or working too long without interruption. It is necessary to observe the standard mode of operation - set moderate current values, use electrodes of small diameters, take breaks in work to cool the device.
Strong heating can lead to a short circuit between the turns of the coil winding due to the combustion of the insulation, usually accompanied by smoke. This is the most serious case, about which they say that the apparatus “burned out”. If this happens, then the repair of the welding machine will require, at best, local restoration of the insulation of the coil wire, at worst, its complete rewinding. In the latter version, in order to preserve the characteristics of the apparatus, it is necessary to rewind with a wire of the original section - with the same number of turns as it was.
Low welding current . The phenomenon can be observed with a low voltage in the supply network or a malfunction of the welding current regulator.
Poor welding current regulation . This can be caused by various malfunctions in the current control mechanisms, which differ in different designs of welding transformers. Namely, malfunctions in the current regulator screw, a short circuit between the regulator terminals, a violation of the mobility of the secondary coils due to the ingress of foreign objects or other reasons, a short circuit in the choke coil, etc. It is necessary to remove the casing from the apparatus and examine the specific current control mechanism for a malfunction. The simplicity of the device of the welding machine and the availability of all its components for inspection facilitate troubleshooting.
Sudden interruption of the welding arc and the inability to re-ignite it . Instead of an arc, only small sparks are observed. This can be caused by a breakdown of the high voltage winding on the welding circuit, a short circuit between the welding wires, or a violation of their connection to the terminals of the device.
High current consumption from the network in the absence of load . This can be caused by a short circuit of the turns of the winding, which is eliminated by local restoration of the insulation or by a complete rewinding of the coil.
The existing electronic part - a diode rectifier and a control module - makes the welding rectifier related to the inverter. Therefore, troubleshooting involves checking the diode bridge and control board elements. The diode bridge is a reliable component of electronic circuits, but sometimes it fails. In general, the causes of a malfunction can be very different: the tracks on the boards burn out, the transformers of the control circuit fail. The photo below shows a case where do-it-yourself repair of a welding machine, which consisted in replacing a non-working part of the control board with a Russian counterpart, allowed the user to save a considerable amount on repairs (70% of the cost of the welding machine).
Unlike a welding transformer, which is more of an electrical product, a welding inverter is an electronic device. This means that the diagnostics and repair of welding inverters involves checking the performance of transistors, diodes, resistors, zener diodes and other elements that make up electronic circuits.You need to be able to work with an oscilloscope, not to mention multimeters, voltmeters and other ordinary measuring equipment.
A feature of the repair of inverters is that in many cases it is difficult or even impossible to determine the failed component by the nature of the malfunction, you have to check all the elements of the circuit in sequence.
From the foregoing, it follows that a successful repair of a welding inverter with your own hands is possible only if you have at least basic knowledge in electronics and little experience in working with electrical circuits. Otherwise, self-repair can only result in a waste of time and effort.
As you know, the principle of operation of a welding inverter is to gradually convert an electrical signal:
Rectification of the mains current - using the input rectifier.
Converting rectified current to high-frequency alternating current - in the inverter module.
Lowering the high-frequency voltage to welding - by a power transformer (having a very small size due to the high voltage frequency).
Rectification of alternating high-frequency current into direct welding - by an output rectifier.
In accordance with the operations performed, the inverter structurally consists of several electronic modules, the main of which are the input rectifier module, the output rectifier module and the control board with keys (transistors).
Although the main components in inverters of various designs remain unchanged, their layout in devices from different manufacturers can vary greatly.
Checking transistors . The weakest point of inverters are transistors, so the repair of inverter welding machines usually begins with their inspection. A faulty transistor is usually immediately visible - a hacked or cracked case, burnt out conclusions. If this is found, you can start repairing the inverter by replacing it. This is what a broken key looks like.
And this is how it was installed instead of the burnt one. The transistor is mounted on thermal grease (KPT-8), which provides good heat dissipation to the aluminum radiator.
Sometimes there are no external signs of a malfunction, all keys look intact. Then, to determine the faulty transistor, a multimeter is used to check them.
Identifying faulty elements is very good, but far from everything. Repair of inverter welding machines also involves looking for, instead of burned out elements, suitable analogues. To do this, the characteristics of the failed elements are determined (according to the datasheet) and, based on it, analogues are selected for replacement.
Checking Driver Elements . Power transistors usually do not fail on their own, most often this is preceded by the failure of the elements of the driver that “swings” them. Below is a photo of the board with elements of the Telwin Tecnica 164 inverter driver. The check is carried out using an ohmmeter. All defective parts are soldered and replaced with suitable counterparts.
Checking rectifiers . Input and output rectifiers, which are diode bridges mounted on a radiator, are considered reliable elements of inverters. However, sometimes they fail too. This does not apply to those shown in the photo below, they are serviceable.
It is most convenient to check the diode bridge by unsoldering the wires from it and removing it from the board. This makes work easier and does not mislead in the presence of a short circuit in the circuit. The verification algorithm is simple, if the whole group rings shortly, you need to look for a faulty (broken) diode.
For soldering parts, it is convenient to use a soldering iron with suction.
control board control . The key control board is the most complex module of the welding inverter; the reliability of the functioning of all components of the device depends on its operation.A qualified repair of welding inverters should end with a check for the presence of control signals coming to the gate busbars of the key module. This check is carried out using an oscilloscope.
Modern equipment for welding various alloys and metals is characterized by a relatively simple design and high operational reliability. Despite this, the repair of welding machines is periodically required even by the most “fancy” units.
Malfunctions of welding machines are most often caused by their improper use, non-compliance by consumers with the recommendations of the equipment manufacturer, as well as natural wear and tear of its individual components. Also, repairs may be required in the following cases:
discrepancy between the magnitude of the current in the power supply and voltage to those indicators that are required for the stable operation of the welding installation;
illiterate connection of equipment to the power source and incorrect completion of work;
welding in contaminated or very damp rooms, in open areas during rain or snow.
As practice shows, most often in welding units the terminal assembly fails, to which the wires necessary for the work are connected.
Cables and various connecting components on it can overheat due to incorrect use of equipment (for example, when using the device for a long time at the highest current value) and due to poor contact.
The insulation of the wires under such conditions begins to melt, which leads to a short circuit. You can cope with the voiced problem with your own hands, it is enough to thoroughly clean the cables and their points of contact with the equipment, and then dock them as tightly as possible.
The presence of any malfunction in the device is usually signaled by the following symptoms:
welding current is difficult to adjust;
spontaneous shutdown of the unit occurs;
the welding arc periodically breaks;
starting the equipment causes certain difficulties (it does not turn on the first time, it turns on and immediately turns off, and so on);
during welding, the unit becomes very hot and hums.
Next, we will talk about what kind of malfunctions are inherent in welding inverters, rectifiers and transformers, and give tips on how to fix them yourself.
VIDEO Now welding inverters are used both in industrial enterprises and by individuals. These units provide real comfort for the welder and guarantee the high quality of the welding process. This is achieved by complicating their design, which, naturally, in most cases reduces the reliability of inverters.
It is not always possible to repair inverter equipment with your own hands, since it is an electronic technique, and not a simpler electrical device (like a transformer or a rectifier for welding). And this means that the diagnosis of unit breakdowns and their elimination require a person to have special knowledge.
To successfully restore the performance of such installations with their own hands, the user must “be on you” with a variety of measurement equipment, from multimeters to oscilloscopes. These devices make it possible to carry out accurate diagnostics of inverters and their electronic “stuffing” (zener diodes, diodes, various transistors, etc.), thereby establishing all the existing malfunctions.
The difficulty of repairing inverter welding machines is that a person must sequentially check the electrical circuit of the unit and find the failed component. Otherwise, nothing will work, since by the nature of the malfunction it is almost impossible to find a “dead” element of welding equipment.
Thus, if you have never dealt with electronics, it makes no sense to repair inverters with your own hands.You will simply waste your energy and lose a lot of time, but you will not achieve anything. Moreover, there is a danger that during such a “repair” you will only aggravate the problem by breaking the electrical circuit.
In those cases, when a person has experience with microcircuits and electrical components, he can easily cope with simple breakdowns of welding inverter equipment. Usually, its malfunctions are detected by carrying out the following checks:
Analysis of the performance of diode bridges (output and input rectifiers) that are mounted on a radiator. They should be dismantled from the board by disconnecting the wiring, and then look for a broken rectifier using the elementary ringing method. Once a non-functioning component is identified, it is replaced with a new one. Experts advise to use a special soldering iron equipped with a suction mechanism to perform such an operation.
Checking the components of the driver. Performed with an ohmmeter. If a failed driver is found, it is unsoldered, a suitable analogue is selected from the datasheet of the device and put in place of the old component.
Transistor testing. In most inverter devices, it is the transistors that most often fail. Finding such an element is not difficult at all, it gives itself out as burnt conclusions, the presence of small cracks on the case. If there are no indicated visible defects, you can ring each transistor with a multimeter, identifying the faulty one.
Welding inverters of our days may have a different layout of elements. But their design is not much different, therefore, do-it-yourself repair of inverter equipment from different manufacturing companies cannot cause difficulties for a person who has an idea of \u200b\u200bthe principles of building electrical circuits.
VIDEO Restoring the normal operation of such devices is easier. Almost any amateur welder can handle self-repair of welding transformers. He usually has to deal with the following malfunctions of welding equipment:
Rewinding the coil, which we talked about, may also be required when there is no load on the equipment, and the device takes a high current from the network. The reason for such a breakdown is the same - the winding is closed.
All other malfunctions of the welding transformer are due to the breakdown of its individual components and components. For example, quite often the current control device fails, its coils (secondary and throttle), into which foreign objects fall during operation. It is not difficult to find such a malfunction due to the simplicity of the design of the transformer for welding.
VIDEO Welding rectifiers are structurally similar to transformers, but they are additionally equipped with mechanisms that are inherent in inverter equipment (control module and diode rectifier). This state of affairs determines the peculiarities of their repair.
If the units of the power unit fail, they are repaired in the same way as welding transformers (the coils are rewound, the insulation between the cables is restored, the regulators and capacitors are changed, etc.). But in case of breakdowns of the control unit and the diode rectifier, the state of the electrical circuit of the device should be analyzed.
Welding semi-automatic equipment can be designed on the basis of rectifiers or inverters. As you yourself understand, it is necessary to repair such units according to the principles described above - the breakdowns will be identical. It should be noted that during the operation of semi-automatic machines, mechanical breakdowns are often recorded, which are caused by the wear of the wire feeder into the welding zone.
In this device, with the active use of welding equipment, increased friction between the channel and the supplied wire can be observed. A similar problem is solved by installing a new channel.It is better not to use other methods of restoring the normal functioning of the device due to their low efficiency.
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