DIY repair of a resant 250 welding inverter

In detail: do-it-yourself repair of the resant 250 welding inverter from a real master for the site my.housecope.com.

Once the Resant SAI 250PN welding inverter fell into my hands. The device, without a doubt, inspires respect.

Those who are familiar with the device of welding inverters will appreciate the power of the electronic filling.

As already mentioned, the filling of the welding inverter is designed for high power. This can be seen from the power section of the device.

The input rectifier has two powerful diode bridges on the radiator, and four electrolytic capacitors in the filter. The output rectifier is also complete with: 6 dual diodes, a massive choke at the output of the rectifier.

three ( ! ) soft start relay. Their contacts are connected in parallel to withstand the large current surge when welding starts.

If we compare this Resanta (Resanta SAI-250PN) and TELWIN Force 165, Resanta will give him a dashing head start.

But, even this monster has an Achilles heel.

The cooling cooler does not work;

There is no indication on the control panel.

After a cursory inspection, it turned out that the input rectifier (diode bridges) turned out to be in good order, the output was about 310 volts. Therefore, the problem is not in the power section, but in the control circuits.

External examination revealed three burned out SMD resistors. One in the gate circuit of the 47 Ohm field-effect transistor 4N90C (marking - 470), and two at 2.4 ohms (2R4) - connected in parallel - in the source circuit of the same transistor.

4N90C bipolar transistor (FQP4N90C) is controlled by a microcircuit UC3842BN... This microcircuit is the heart of the switching power supply, which powers the soft-start relay and the integrated stabilizer at + 15V. He, in turn, feeds the entire circuit, which controls the key transistors in the inverter. Here is a piece of the RESant SAI-250PN diagram.

Video (click to play).

It was also found that there is also a resistor in the power circuit of the UC3842BN (U1) ShI controller in the open circuit. In the diagram, it is designated as R010 (22 ohm, 2W). It has the reference designation R041 on the printed circuit board. I will warn you right away that it is quite difficult to detect a break in this resistor during an external examination. A crack and characteristic burns can be on the side of the resistor that faces the board. This was the case in my case.

Apparently, the cause of the malfunction was the failure of the UC3842BN (U1) ShI controller. This, in turn, led to an increase in the consumed current, and the resistor R010 burned out from a sharp overload. SMD resistors in the FQP4N90C MOSFET circuits played the role of a fuse and, most likely, thanks to them, the transistor remained intact.

As you can see, the whole switching power supply unit on the UC3842BN (U1) has failed. And it feeds all the main units of the welding inverter. Including soft start relay. Therefore, welding did not show any "signs of life."

As a result, we have a bunch of "little things" that need to be replaced in order to revive the unit.

After replacing the indicated elements, the welding inverter turned on, the display showed the value of the set current, the cooling cooler clinked.

For those who want to independently study the device of the welding inverter - the complete schematic diagram of "Resant SAI-250PN".

Repair of welding inverters, despite its complexity, in most cases can be done independently. And if you are well versed in the design of such devices and have an idea of what is more likely to fail in them, you can successfully optimize the costs of professional service.

Replacement of radio components in the process of repairing a welding inverter

The main purpose of any inverter is to generate a constant welding current, which is obtained by rectifying a high-frequency alternating current. The use of a high-frequency alternating current, converted by means of a special inverter module from a rectified mains supply, is due to the fact that the strength of such a current can be effectively increased to the required value using a compact transformer. It is this principle underlying the operation of the inverter that allows such equipment to be compact in size with high efficiency.

Functional diagram of the welding inverter

The welding inverter circuit, which determines its technical characteristics, includes the following main elements:

a primary rectifier unit, the basis of which is a diode bridge (the task of such a unit is to rectify an alternating current coming from a standard electrical network);
an inverter unit, the main element of which is a transistor assembly (it is with the help of this unit that the direct current supplied to its input is converted into an alternating current, the frequency of which is 50–100 kHz);
a high-frequency step-down transformer, on which, due to a decrease in the input voltage, the output current is significantly increased (due to the principle of high-frequency transformation, a current can be generated at the output of such a device, the strength of which reaches 200–250 A);
output rectifier, assembled on the basis of power diodes (the task of this block of the inverter includes rectifying an alternating high-frequency current, which is necessary for performing welding).

The welding inverter circuit contains a number of other elements that improve its operation and functionality, but the main ones are the above.

Repair of an inverter-type welding machine has a number of features, which is explained by the complexity of the design of such a device. Any inverter, unlike other types of welding machines, is electronic, which requires specialists involved in its maintenance and repair to have at least basic radio engineering knowledge, as well as skills in handling various measuring instruments - a voltmeter, digital multimeter, oscilloscope, etc. ...

In the process of maintenance and repair, the elements that make up the welding inverter circuit are checked. This includes transistors, diodes, resistors, zener diodes, transformer and choke devices. The peculiarity of the design of the inverter is that very often during its repair it is impossible or very difficult to determine the failure of which particular element was the cause of the malfunction.

A sign of a burnt out resistor may be a small carbon deposit on the board, which is difficult to distinguish with an inexperienced eye.

In such situations, all the details are checked sequentially. To successfully solve such a problem, it is necessary not only to be able to use measuring instruments, but also to be quite familiar with electronic circuits. If you do not have such skills and knowledge at least at the initial level, then repairing a welding inverter with your own hands can lead to even more serious damage.

Realistically assessing their strengths, knowledge and experience and deciding to undertake independent repair of inverter-type equipment, it is important not only to watch a training video on this topic, but also to carefully study the instructions, in which manufacturers list the most typical malfunctions of welding inverters, as well as ways to eliminate them.

Situations that can cause the failure of the inverter or lead to malfunctions can be divided into two main types:

associated with the wrong choice of welding mode;

caused by the failure of parts of the device or their incorrect operation.

The technique for detecting an inverter malfunction for subsequent repair is reduced to the sequential performance of technological operations, from the simplest to the most complex. The modes in which such checks are performed and what their essence is, is usually specified in the equipment instructions.Common inverter malfunctions, their causes and remediesIf the recommended actions did not lead to the desired results and the operation of the device has not been restored, most often this means that the cause of the malfunction should be looked for in the electronic circuit. The reasons for the failure of its blocks and individual elements may be different. Let's list the most common ones.

Moisture has penetrated into the interior of the device, which can happen if precipitation falls on the body of the device.

Dust has accumulated on the elements of the electronic circuit, which leads to a violation of their full cooling. The maximum amount of dust gets into inverters when they are used in highly dusty rooms or on construction sites. In order not to bring the equipment to such a state, its interior must be regularly cleaned.

Overheating of the elements of the electronic circuit of the inverter and, as a consequence, their failure can lead to non-observance of the duration of the switch (DC). This parameter, which must be strictly observed, is indicated in the technical passport of the equipment.

Liquid traces inside the inverter housingThe most common problems encountered when operating inverters are as follows.Unstable arc burning or active metal spatter This situation may indicate that the wrong amperage has been selected for welding. As you know, this parameter is selected depending on the type and diameter of the electrode, as well as on the speed of welding. If the packaging of the electrodes that you are using does not contain recommendations on the optimal value of the current strength, you can calculate it using a simple formula: 1 mm of the electrode diameter should account for 20–40 A of welding current. It should also be borne in mind that the lower the welding speed, the lower the current must be.Dependence of the diameter of the electrodes on the strength of the welding currentThis problem can be associated with a number of reasons, and most of them are based on undervoltage. Modern models of inverter devices also operate at reduced voltage, but when its value drops below the minimum value for which the equipment is designed, the electrode begins to stick. A drop in the voltage value at the output of the equipment can occur if the units of the device are poorly in contact with the panel sockets.This reason can be eliminated very simply: by cleaning the contact sockets and fixing the electronic boards in them more tightly. If the wire through which the inverter is connected to the mains has a cross section of less than 2.5 mm2, this can also lead to a voltage drop at the input of the device. This is guaranteed to happen even if such a wire is too long.If the length of the supply wire exceeds 40 meters, it is practically impossible to use an inverter for welding, which will be connected with its help. The voltage in the supply circuit can also drop if its contacts are burnt or oxidized. A frequent cause of electrode sticking is insufficiently high-quality preparation of the surfaces of the parts to be welded, which must be thoroughly cleaned not only from the existing contaminants, but also from the oxide film.Selection of the cross-section of the welding cableThis situation often occurs in the event of overheating of the inverter device. At the same time, the control indicator on the panel of the device should light up.If the glow of the latter is hardly noticeable, and the inverter does not have a sound alert function, then the welder may simply not be aware of overheating. This state of the welding inverter is also typical when the welding wires are broken or spontaneously disconnected.Spontaneous shutdown of the inverter during welding Most often, this situation occurs when the supply of the supply voltage is turned off by circuit breakers whose operating parameters are incorrectly selected. When working with an inverter device, automatic machines designed for a current of at least 25 A must be installed in the electrical panel.

The way of operation of the Resanta sai 250 welding machine and its circuit do not differ from similar devices of other manufacturers. The incoming AC current of a conventional 220 V power grid is converted first to direct current, with a value of 400 V, which is then changed to a modulated high-frequency voltage. After that, a step-down transformer is turned on, which reduces the converted current to a working state.

The principle of operation of the inverter is based on converting an alternating current of 50 Hertz from a conventional household power supply into a direct current. This voltage indicator has a magnitude of 400 volts... The current of the welding machine is regulated by modulation (by and large, it is a wide-pulse) of the obtained high-frequency voltage.

The considered device for welding Resant SAI is made in a steel case. On the outer part of this body there are power connectors for connecting welding cables, two indicators ("Mains" and "Overheating"), a regulator for selecting the characteristics of the welding current. Also in the case there is a special hole through which hot air is removed from the device. It is part of a forced ventilation system that protects the inverter from extreme overheating during operation.

The Resant Sai inverter also has one more protection system, it automatically turns off the device in cases where power cords are short-circuited. Moreover, the corresponding indicator on the front control panel starts blinking. The inverter is distinguished by the presence of several important functions that are often used during operation:

Hot start guarantees fast and high-quality ignition of the welding arc due to an increase in the level of the welding current (the worker does not need to do anything, the current increases in automatic mode). And the anti-stick mode, on the contrary, reduces the welding current if, during the ignition of the arc, adhesion of the welding wire (electrode) is noted. Then, when the adhesion is removed, the welder automatically restores the welding performance on its own.

The main advantage of this welding inverter for household needs of consumers is that it is specially adapted for connection in those power grids in which low voltage of the mains (130-250 Volts)... Resant SAI works without interruptions at the specified voltage when welding in manual arc mode.

You can use rods for welding up to 6.0 mm. The welding current in the device can be adjusted up to 250A. It is also important that the device is able to withstand rather heavy workloads for a long time. This property positively distinguishes its scheme of work from other devices, which are found in abundance on the windows of specialized hardware stores.

Idling Resanta SAI's welding device operates with a voltage of 80 Volts. The durability of the device at a fairly high power is ensured in its circuit by the design of modern high-quality IGBT transistors. In addition, this welding inverter has a high degree of protection - IP 21 protection level.

One cannot fail to mention the compactness of this welding machine, as well as its excellent mobility. Equipped with a handle for carrying the device, it makes it easier to carry it around the territory of the site where the construction is taking place. Also, consumers note the accuracy and simplicity of setting up the Resant sai welding inverter. At the same time, the specified indicators are guaranteed to retain the established data even in cases where the electrical network does not differ in the stability of its voltage indicators.

Specifications The Resant SAI apparatus of interest to us is as follows:

maximum consumption current - 35 Amperes;
load duration at 250 Amperes - not less than 70%;
welding adjustment interval - 10-250 Amperes;
working temperature range of the environment - -10 / + 40C;
arc voltage - 30 Volts.

If necessary, this device can be connected to the equipment of a generator that runs on gasoline. It is best to choose a generator with a power of more than five kilowatts.

Attention! When choosing a welding electrode (the electrode can be no more than 6 millimeters in diameter), it must also be taken into account that the welding current decreases when the input current decreases.

The scheme for preparing the welding device for operation is quite simple, but it must be performed as accurately as possible if you want the device to serve you for a long time and without repair. First of all, you need to connect the cord with an electric holder and the ground wire to the power terminals of the device (you must definitely pay attention to the polarity of the welding rod that you are using).

Read also: DIY velor repair

Put the regulator for minimum welding current, then you can connect the inverter to the power grid, and then turn it on. The required level of welding current must be selected based on the indicators recommended by the manufacturer of Resant SAI:

200-300 Amperes - electrode diameter 6 millimeters;
160-200 Amperes - 5 millimeters;
130-160 Amperes - 4 millimeters;
90-140 Amperes - 3.2 millimeters;
60-90 Amperes - 2.5 millimeters;
50-60 Amperes - 2 millimeters;
25-50 Amperes - 1.6 millimeters.

After welding, the current is set to the minimum value by means of the regulator, the inverter is turned off (first by a switch, and then from the mains). Also, disconnect the electrical holder and grounding cord from the apparatus.

Before switching on, the device must be kept at a positive air temperature for several hours. Otherwise, condensation may form in it, which may damage the inverter. It is strictly forbidden to operate the device in cases where its welding cords or the wire connecting to the mains are deformed (even slight).

Near a switched on welding machine, you must not process metal and steel parts using grinders, electric jigsaws and similar equipment, during which metal dust appears... Dust can enter the cabinet and damage the inverter. In addition, it is forbidden to operate the unit in open areas in the rain or in rooms with high humidity.

Before operating the Resant SAI inverter, it is imperative to study the "Safety Rules for Users of Electrical Devices" and "Rules for the Operation of Household Electrical Installations". During operation welding machine you need:

create access to fresh air in the room where the welding work is carried out (when welding takes place in the room, then it must be well ventilated);
work in a welding protective mask, gloves, a headdress and special clothing that protects the body from possible thermal burns;
comply with fire safety rules.

It is necessary to store the welding device in rooms where the formation of acidic or alkaline vapors is excluded, and there is no excessive dustiness. Optimum characteristics for storing the device:

temperature - not higher than +55 and not lower than -15 degrees;
relative humidity - no more than 70 percent.

The operating reserve and potential of this inverter is quite high. The device is classified by many foreign experts as one of the best in its group. When used correctly, this equipment repairs may not be required for years (even if the inverter is used quite actively). But, of course, there is no eternal equipment, so you need to be prepared for the fact that the welding device will probably need to be repaired.

It is best to do the repairs by the craftsmen (in many localities there are authorized centers that deal with the equipment of the "Resanta" company). Moreover, the user can fix some minor breakdowns with his own hands. For example, when on the control panel overheating indication appears, then you need to clean the device from dust accumulated in it.

But, if the welding machine cannot reach maximum power, then drying the electrode, which is used for welding, can help. It is often the damp welding rod that causes poor equipment performance. The same problem appears in cases where the voltage in the electrical network is very weak.

Image - DIY repair of a resant 250 welding inverter

Is your TV, radio, mobile phone or kettle broken? And you want to create a new topic about this in this forum?

First of all, think about this: imagine that your father / son / brother has an appendicitis pain and you know from the symptoms that it is just appendicitis, but there is no experience of cutting it out, as well as the tool. And you turn on your computer, access the Internet on a medical site with the question: "Help to cut out appendicitis." Do you understand the absurdity of the whole situation? Even if they answer you, it is worth considering factors such as the patient's diabetes, allergies to anesthesia and other medical nuances. I think no one does this in real life and will risk trusting the life of their loved ones with advice from the Internet.

The same is in the repair of radio equipment, although of course these are all the material benefits of modern civilization and in case of unsuccessful repairs, you can always buy a new LCD TV, cell phone, iPAD or computer. And for the repair of such equipment, at least it is necessary to have the appropriate measuring (oscilloscope, multimeter, generator, etc.) and soldering equipment (hairdryer, SMD-hot tweezers, etc.), a schematic diagram, not to mention the necessary knowledge and repair experience.

Let's consider a situation if you are a beginner / advanced radio amateur soldering all sorts of electronic gizmos and having some of the necessary tools. You create an appropriate thread on the repair forum with a short description of “patient symptoms”, ie. for example “Samsung LE40R81B TV does not turn on”. So what? Yes, there can be a lot of reasons for not switching on - from malfunctions in the power system, problems with the processor or flashing firmware in the EEPROM memory.
More advanced users can find the blackened element on the board and attach a photo to the post. However, keep in mind that you are replacing this radio element with the same one - it is not yet a fact that your equipment will work. As a rule, something caused the combustion of this element and it could “pull” a couple of other elements along with it, not to mention the fact that it is quite difficult for a non-professional to find a burned-out m / s. Plus, in modern equipment, SMD radio elements are almost universally used, soldering which with an ESPN-40 soldering iron or a Chinese 60-Watt soldering iron you risk overheating the board, peeling tracks, etc. The subsequent restoration of which will be very, very problematic.

The purpose of this post is not any PR of repair shops, but I want to convey to you that sometimes self-repair can be more expensive than taking it to a professional workshop. Although, of course, this is your money and what is better or more risky is up to you.

If you nevertheless decide that you are able to repair the radio equipment on your own, then when creating a post, be sure to indicate the full name of the device, modification, year of manufacture, country of origin and other detailed information. If there is a diagram, then attach it to the post or give a link to the source. Write down how long the symptoms have been manifesting, whether there were surges in the supply voltage network, whether there was a repair before that, what was done, what was checked, voltage measurements, oscillograms, etc.From a photo of a motherboard, as a rule, there is little sense, from a photo of a motherboard taken on a mobile phone there is no sense at all. Telepaths live in other forums.
Before creating a post, be sure to use the search on the forum and on the Internet. Read the relevant topics in the subsections, perhaps your problem is typical and has already been discussed. Be sure to read the article Repair strategy

The format of your post should be as follows:

Topics with the title “Help fix the Sony TV” with the content “broken” and a couple of blurred photos of the unscrewed back cover, taken with the 7th iPhone, at night, with a resolution of 8000x6000 pixels are immediately deleted. The more information you post about the breakdown, the more chances you will get a competent answer. Understand that the forum is a system of gratuitous mutual assistance in solving problems and if you are dismissive of writing your post and do not follow the above tips, then the answers to it will be appropriate, if anyone wants to answer at all. Also keep in mind that no one should answer instantly or during, say, a day, no need to write after 2 hours “That no one can help”, etc. In this case, the topic will be deleted immediately.
You should make every effort to find a breakdown on your own before you get stumped and decide to go to the forum. If you outline the entire process of finding a breakdown in your topic, then the chance of getting help from a highly qualified specialist will be very great.

If you decide to take your broken equipment to the nearest workshop, but do not know where, then perhaps our online cartographic service will help you: workshops on the map (on the left, press all buttons except “Workshops”). You can leave and view user reviews for workshops.

For repairmen and workshops: you can add your services to the map. Find your object on the map from the satellite and click on it with the left mouse button. In the field “Object type:” do not forget to change to “Equipment repair”. Adding is absolutely free! All objects are checked and moderated. A discussion of the service is here.

The fact that the impulse feeder often fails in Resant's inverters is a fairly well-known fact, this inverter was a confirmation of this - the UPS is the weak link of these devices, although in general Resant is quite good welders and is quite maintainable.

But, as they say, repetition is a mother. something there. so let's run at a light gallop over a similar defect.

So: Resanta SAI 250 inverter does not start.

Carbon deposits are visible under the resistor R010, most likely it burned out. Resistor R013 is clearly burned out. All this suggests that the switching power supply is out of order.

Now we check.
Resistor R010 22 Ohm 2 W - through it power is supplied to the primary winding of TPI - cut off.
Resistor R013 1.2 Ohm - stands at the source of the Q02 4N90C transistor - cut off.
Resistor R011 22 Ohm - stands in the gate of the same transistor - is cut off.
Zener diode D012 18 volts - intact.
Transistor Q02 4N90C - int.

There is a chance that everything will be bypassed by replacing these three resistors.

In the video, a hum is heard from a broken fan. But we'll figure it out with the fan later, and now the main thing is that everything has turned on. This is already pleasing.

Now we change all the killed resistors. It is worth saying that instead of R010 22 Ohm 2 W in these devices, economical brothers from the Celestial Empire usually put a one-watt 22 Ohm resistor.

It will be safer this way. We check the inverter again.

Video: Resant's SAI 250 welding inverter after repair.

As you can see from this video, a pun :), everything starts up fine. Which is what we wanted.

And "on the road" the mode of operation of the UC3842B microcircuit, just in case all the above operations do not lead to the desired result.

Attention!
It is IMPOSSIBLE to predict all the nuances that arise during the repair of welding inverters. If in doubt, it is better to consult a specialist.

Repair of welding inverters from Resant and other manufacturers.

electrodroid, well, where are the measurements? 1. PROF is a device with PFC and it will not work with a light bulb stably.2. What are the voltages at the output of the power supply unit, and what happens to them when the device works (without wind generators)? 3. Everything that “crunches”, either to be repaired or replaced.

electrodroid, did you change the power transistor in the duty room? If you did, then take a very close look at the board - between the drain and the gate-source leads there is a secondary circuit track (hammer a rusty nail into the back of the head of the one who bred this board

) When humid metal dust accumulates in this place, miracles with fireworks begin and fans first of all become victims of these miracles.

A device from 100 V should start up and work according to the factory specifications, this is not the first such device I check through a light bulb after repairs (only at idle speed, of course!) After the light bulb, about 165 V goes to the device, it is enough for the inverter to start. Without fans, all power supply voltages are normal, only the green indicator is on. At the output (+) (-) 65 V, no-load welding voltage.

NAMELESS, The transistor in the TO-247 package, holes are punched through between the pins on the board, there are no tracks.

electrodroid, so I came across a different version of the board.

The problem was with the VO3120 driver and its binding.

And you can get more details

I have about everything the same on Resant 220, with fans the power supply unit BOOM! (22 Omnik / 2W and 10kOhm / 3W go into the smoke) but without a wind turbine, everything is fine. The oscillograms on the keys seem to be beautiful, but how can you sin on the drivers?

vldmrtu, if everything is good without wind turbines and bad with them, then what should be checked? Or is there no source to check?

Check the fans? consumption is within 0.4a each, the power supply on duty also burns out from one fan, from the nuances I can note the 51Ohm resistor at the mains power input was also burnt out, temporarily put a jumper, can the absence of current limitation at the moment of switching on burn the power supply? it seems to be yes, but somehow it is not obvious.

You can put 1-2 diodes in series with the fan. To reduce the current a little. Starting cut. it is advisable to put at the entrance, maybe 51 is too much, up to 10 is enough,
or posistor. you can take it from a dead power supply from a computer.

0.4a is the operating current of the fan, and what is the starting current? Apply how many volts there and slow down the blades, measure the current.

And what is the operating current written on the nameplate of the fans? Turning on without a resistor is fraught with the departure of the bridge diodes at least, but if the diodes and capacitors survived, then the rest will not die from this, the rating is not very important there, because after starting the duty room, the relay (if it is alive) still closes it.

I put the fans aside for now and went from the other side. I tried to start the invector at a reduced voltage, powered it up with some 10kg of trance and got 83 volts on the capacitors, DOES NOT START! (I tried other resants and started up fine). I cut off the track on the power supply of the drivers - there is no effect. Replacing the hopelessness of the LM317 also gave nothing.

Fans weren't the reason for the BOOM! power supply, rather they were the last straw.
What remains: unexplained UC3842 behavior, transistor or trance glitches?

Let's take a look at one of my "clients" today, namely the "Resanta - SAI 250 PROF" welding inverter. Why a client, because the malfunction with which he came to me on the desktop was the most frequent in this kind of welding machines - secondary power supply, or it is also called the "standby source".

You can order the elements listed in the article for repairing the Resant welding inverter - SAI 250 PROF on Ali:

1) Shim controller SG6859 - https://ali.pub/2pd1gz

2) Field effect transistor SPD06N80C3 - https://ali.pub/2pd1qb

3) Controller TOP 224 - https://ali.pub/2pd244

So, this friend is assembled in this welding machine for shim controller SG6859 and field-effect transistor SPD06N80C3 there is no need to list the strapping and everything else.

What is the salt you ask. Here's the thing. When a field worker punches it, he pulls the PWM controller and a small part of the harness with him.Finding the parts I need on the radio market is very difficult. But thank God we have Chinese (what would we do without them) that's where I ordered them. The cost is ridiculous, but the terms are long, which did not really suit me. But this also has its advantages.

The person who brought me the welding machine, due to the rather long delivery time for the original parts, offered me to buy it back. We bargained and I bought a damaged "friend" SAI 250 PROF from him for 3500 rubles. Of course, I knew that it cost me 450 rubles to repair it. But knowing the price that it was worth, I did not think for a long time, took out the cherished ever-wooden and settled with the person and proceeded to repair the Resant welding inverter

Without waiting for the details to arrive (my hands were itching), without hesitation, I figured out a small alteration from the Internet and everything worked out for me.

The alteration is as follows:

We take a microcircuit TOP 224 (223, 204, 203)

We remove the field-effect transistor;
We remove the PWM controller;
We unsolder the emitter of the optocoupler U8 (participating in the feedback with the PWM) and chorus it to the "control" pin TOP 2xx; We connect the collector to the "+" supply PWM via contact No. 5 -VDD. You can take it from the positive terminal of the C30 capacitance;
Drain or (Drain) to the place of the drain of the former SPD06N80C3 (the largest site);
Source to place of source SPD06N80C3;
Solder the capacitor between the source and the gate (control) 47 uF - 50V, "-" to the source.
Instead of resistances 1.3 Ohmx3, we solder the resistance 6.8 Ohm.

That's all. We launch it and everything works.

Here is a photo of the revision (from the Internet) not my invention:

Below is the second option. Personally, I did it first.

So, after some minor manipulations, I have a SAI 250 PROF welding machine from RESANT. The device is very good, decent and certainly worth the money. Amendment - the money that I paid for it - 3500 rubles. 🙂

Datasheet on TOP 22x (1,2,3,4,5,6,7) - Download

Passport for RESANTA SAI-250 PROF - Download

Video (click to play).

Welding machine diagram RESANTA SAI-250 PROF - Download

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