A semiautomatic welding machine is an electrical apparatus designed for the welding process using an electrode.
Structurally, the welding semiautomatic device is equipped with electronics with high frequencies. The latter tends not only to increase the efficiency of the units, but also often show its "capricious" character.
The repair procedure for an inverter semiautomatic welding machine (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 the part that has become unusable.
If no external changes are observed, then they are taken for diagnostics.
Diagram of a semiautomatic welding device.
First, they check the fuses on the control board. By means of a tester or an ohmmeter, the broken element is calculated by dismantling the board. Having found it, they carefully change it to a new one and reassemble the semiautomatic device. When all starters are working, they look for the problem further, analyzing possible circuit malfunctions.
Often, the repair of a semiautomatic welding machine is associated with malfunctions of field-effect transistors, which are the weakest point. Symptoms of malfunctions (they were mentioned above) externally in this group of elements do not manifest themselves at all. It is extremely rare that the case can crack and the leads melt. These features force us to search for burnt-out transistors by ringing them in turn with a multimeter.
Another point of diagnostics is the control of the components of the driver, which is responsible for the functioning of field-effect transistors. Items that have fallen into disrepair can be determined by means of an ohmmeter.
Welding rectifier circuit.
Please note: in order not to be confused, it is recommended that both the driver elements and the transistors ring out relative to the circuit of the existing inverter semiautomatic device, choosing the direction in advance (for example, from top to bottom). In this case, the risk of not taking into account something or missing any element will be reduced to zero.
If the malfunction 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 probability of their breakdown.To diagnose the diodes located on the radiators, they are wired from the board. The working diode changes resistance from plus to minus and vice versa. With different test results, the diodes are thrown out.
Repair of a semiautomatic device upon detection of the malfunctions described above is reduced to replacing the failed components.
Overheating is often the cause of transistor malfunctions. In case of checking the inside of the unit, it will be useful, just in case, to change the thermal grease at the points of contact with the heat sink plate.
And in case of repairing a breakdown, you can go over the contacts. Those that do not seem very neat are cleaned and connected.
Self-repair of a semiautomatic welding machine is a rather favorite process among craftsmen who often perform body work.
Welding transformer diagram.
But it is not always possible. Although, with a minor breakdown, an attempt to find it may not be meaningless.
One of the problems that does not require mandatory professional intervention is the sticking of the electrode when the amperage is selected correctly. The following factors are the causes of breakdowns:
If the welding arc is unstable or the wire used is incompletely melted, the contact tip may have become unusable or the grounding clamp is incorrectly connected. To get rid of inconvenience in the work, the tip is replaced and the clamping area is cleaned of dirt.
Shielding gas failures resulting in poor weld quality can be caused by breakage of the gas diffuser. The problem is solved by replacing the element.
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So, most of the problems are eliminated by changing the quickly wearing parts of the welding machine. When all actions do not help, they resort to the help of a service center, which 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. Poor contact together with a high welding current leads to 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 a welding transformer in this case is reduced to sorting out the heating connection, cleaning the contact surfaces and clamping them, ensuring 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 can occur due to short circuits in the high voltage circuit - between the wires and the case, or wires between themselves. A short circuit between the turns of the coils or sheets of the magnetic circuit, as well as the breakdown of capacitors, can also trigger 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 humming of the transformer , often accompanied by overheating. The reason may be loosening of the bolts tightening the sheet elements of the magnetic circuit, malfunctions in the fastening of the core or the mechanism for moving the coils, overloading of the transformer (excessively long operation, high value of the welding current, large diameter of the electrode). A short circuit between welding cables or sheets of a magnetic circuit also leads to a strong hum.It is necessary to check and tighten all screws and bolts, eliminate irregularities in the mechanisms for fixing 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 too long work without interruption. It is necessary to observe the standard operating mode - 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 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 happened, then the repair of the welding machine will require, at best, a local restoration of the coil wire insulation, 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 undervoltage in the supply network or a malfunction of the welding current regulator.
Poor welding current adjustment ... This can be caused by various faults in the current control mechanisms, which differ in different designs of welding transformers. Namely, malfunctions in the screw of the current regulator, a short circuit between the terminals of the regulator, 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 cover from the apparatus and investigate the specific current control mechanism for detecting a malfunction. The simplicity of the device of the welding machine and the accessibility of all its components for inspection facilitate troubleshooting.
A sudden break in the welding arc and the inability to ignite it again ... Instead of an arc, only small sparks are observed. This can be caused by a breakdown of the high voltage winding to the welding circuit, a short circuit between the welding wires or a disruption in their connection to the terminals of the machine.
Consumption of large current from the network at no load ... This can be caused by a short circuit of the winding turns, which is eliminated by a local restoration of insulation or a complete rewinding of the coil.
The available electronic part - a diode rectifier and a control module - makes the welding rectifier akin to an inverter. Therefore, troubleshooting involves checking the diode bridge and elements of the control board. A diode bridge is a reliable component in electronic circuits, but sometimes it fails. In general, the causes of the malfunction can be very different: the tracks on the boards burn out, the control circuit transformers fail. The photo below shows a case when repairing a welding machine with your own hands, which consisted of replacing a non-working part of a control board with a Russian analogue, 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 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 inverter repair is the fact that in many cases it is difficult or even impossible to determine by the nature of the malfunction a failed component, you have to check all the elements of the circuit sequentially.
From the foregoing, it follows that the successful repair of a welding inverter with your own hands is possible only if you have at least initial 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 a step-by-step conversion of an electrical signal:
Rectifying the mains current - using an input rectifier.
Converting the rectified current into high-frequency alternating current - in the inverter module.
Lowering the high-frequency voltage to the welding voltage - with a power transformer (very small in size due to the high frequency of the voltage).
Rectification of alternating high-frequency current into constant 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).
While the main components in inverters of different designs remain unchanged, their layout in devices from different manufacturers can vary greatly.
Checking transistors ... The weakest point of inverters is the transistors, so the repair of inverter welding machines usually begins with their inspection. A faulty transistor is usually visible immediately - a cracked or cracked case, burned-out leads. If such is found, you can start repairing the inverter by replacing it. This is what a burnt key looks like.
And this is how it was installed instead of the burnt one. The transistor is installed on thermal paste (KPT-8), which provides good heat dissipation to the aluminum radiator.
Sometimes there are no external signs of malfunction, all keys appear to be intact. Then, to determine the faulty transistor, a multimeter is used to dial them.
It is very good to identify faulty items, but not all. Repair of inverter welding machines also involves the search, instead of burnt out elements, suitable analogues. For this, the characteristic of the failed elements is determined (according to the datasheet) and, based on it, analogues are selected for replacement.
Checking Driver Items ... Power transistors usually do not fail by themselves, most often this is preceded by the failure of the elements of the "swinging" their driver. Below is a photo of the board with the elements of the Telwin Tecnica 164 inverter driver. The check is carried out using an ohmmeter. All defective parts are soldered out and replaced with suitable analogs.
Rectifier test ... Input and output rectifiers, which are diode bridges mounted on a radiator, are considered reliable elements of inverters. However, sometimes they also fail. This does not apply to those shown in the photo below, they are serviceable.
The diode bridge is most conveniently checked by unsoldering the wires from it and removing it from the board. This makes it easier to work and is not misleading if there is a short circuit in the circuit. The verification algorithm is simple, if the whole group is short-circuited, you need to look for a faulty (punctured) diode.
It is convenient to use a suction soldering iron to solder parts.
Control board monitoring ... 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 busbars of the gates of the key module. This check is carried out using an oscilloscope.
Modern equipment for welding various alloys and metals is distinguished by a relatively simple design and high operational reliability. Despite this, the repair of welding machines is periodically required even by the most "sophisticated" units.
Malfunctions of welding machines are most often caused by their incorrect use, non-compliance by consumers with the recommendations of the manufacturer of the equipment, as well as natural wear and tear of its individual units. Also, repairs may be required in the following cases:
inconsistency of the current in the power supply and voltage with those indicators that are required for the stable operation of the welding installation;
illiterate connection of equipment to a power source and incorrect completion of work;
welding in dirty or very humid rooms, in open areas during rain or snow.
As practice shows, most often in welding units, the terminal node fails, to which the wires are connected, which are necessary to perform the work.
Cables and various connecting components on it can overheat due to improper use of technology (for example, with prolonged use of the device at the highest current value) and due to poor contact.
Under such conditions, the insulation of the wires begins to melt, which leads to a short circuit of the electrical circuit. You can cope with the voiced problem with your own hands, it is enough to thoroughly strip the cables and the places of their contact with the equipment, and then dock them together as tightly as possible.
The presence of any malfunction in the device is usually signaled by the following symptoms:
the welding current is difficult to adjust;
there is a spontaneous shutdown of the unit;
the welding arc is interrupted periodically;
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 malfunctions are inherent in welding inverters, rectifiers and transformers, and give advice on how to fix them yourself.
VIDEO Now welding inverters are used both in industrial enterprises and individuals. These units provide real comfort for the welder and guarantee a high quality of the welding process. This is achieved due to the complication of 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 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 operability of such installations with their own hands, the user must “be on the hook” 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, all kinds of transistors, etc.), thereby establishing all existing faults.
The difficulty of repairing inverter welding machines is that a person must consistently 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 the “dead” element of the welding equipment.
Thus, if you have never dealt with electronics, there is no point in doing inverter repairs with your own hands. You will simply waste energy and waste 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 disrupting the electrical circuit.
In the same cases, when a person has experience with microcircuits and electrical components, he may well cope with simple breakdowns of welding inverter equipment. Typically, its malfunctions are detected during the following checks:
Analysis of the performance of diode bridges (output and input rectifiers), which are mounted on a radiator. They should be dismantled from the board by disconnecting the wiring, and then look for a punched rectifier using the elementary ringing method. After identifying a non-functioning component, 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. When a failed driver is found, it is soldered off, a suitable analog is selected from the device datasheet and replaced by the old component.
Inspection of transistors. In most inverter devices, it is the transistors that most often fail. Finding such an element is not difficult at all, it betrays itself with burnt leads, the presence of small cracks on the case. If there are no indicated visible defects, you can ring each transistor with a multimeter, determining the faulty one.
Welding inverters today can have a different arrangement of elements. But at the same time, their design does not differ much, therefore, do-it-yourself repair of inverter equipment from different manufacturers cannot cause difficulties for a person who has an idea of \ u200b \ u200bthe principles of constructing electrical circuits.
VIDEO Restoring normal operation of such devices is easier. Self-repairing welding transformers can be done by almost any amateur welder. Usually he has to deal with the following malfunctions of welding equipment:
The rewinding of 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 caused by the breakdown of its individual units and components. For example, the current control device and its coils (secondary and choke) often fail, into which foreign objects fall during operation. Finding such a malfunction is easy 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 nodes of the power unit fail, they are repaired in the same way as welding transformers (rewinding coils, restoring insulation between cables, changing regulators and capacitors, etc.). But in case of breakdowns of the control unit and the diode rectifier, the state of the electrical circuit of the apparatus should be analyzed.
Semi-automatic welding 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. Note that during the operation of semiautomatic devices, mechanical breakdowns are often recorded, which are caused by wear of the wire feed device to the welding zone.
In the specified device, with the active use of welding equipment, increased friction between the channel and the supplied wire can be observed. This problem is solved by installing a new channel. It is better not to use other methods of restoring the normal functioning of the apparatus due to their low efficiency.
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