DIY arc 200 repair

In detail: do-it-yourself arc 200 repair from a real master for the site my.housecope.com.

Hello everyone. I am with you again, a welder repairman. So today we received another failed welding inverter. Among our repairmen, such devices are called three-story buildings.

Declared malfunction: Does not produce welding current. Sparks and does not cook.

By the way, you can see three floors of the board inside,

the first is a board with conductors and soft start.

the second is the rectifier, choke, and power trance.

the third is mosfet transistors, a duty room and a control board.

Since the cause of the breakdown is stated to be low current and does not cook, we will check the OS by current. These three-story buildings have a sore spot for the current.

The CA3140 microcircuit is responsible for controlling the current in this welder.

And if we have something wrong in the current control chain, two LEDs light up. In my case, these LEDs were on.

Further punching in the control board revealed a faulty CA3140. Conclusions 2 and 3 rang among themselves at 4 ohms.

Further, my welder stupidly turned off in the cold, that is, the welding flew away completely out, not a single sign of life. At room temperature, it restored its working capacity, but as soon as I cooled it down, it refused to work. The malfunctions were a little chaotic, so I had to run from home to the street and vice versa to catch GLUCK and analyze the reasons.

By malfunction, it could be said that I did not have + 300V from the rectifier board and capacitors (the first bottom board). Therefore, when I once again caught a glitch, I threw the multimeter probes onto the two power lines of the welder. And he was surprised. There, instead of 300v, it was only 100v. Hmm, strange.

Video (click to play).

I took out the lower board and washed it. And he began to look at what was wrong.

I was attracted by a black coating under the relay, as if something was fucking there.

I unsolder it. By the way, when I was soldering, I was confused by the fact that the pin from the relyushka was visible in the penny, and the soldering iron did not feel it. As it turned out later, the output from the relay was short, or rather it was not really there at all. And because of this, the welding did not start.

The main element of the simplest welding machine is a transformer operating at a frequency of 50 Hz and having a power of several kW. Therefore, its weight is tens of kilograms, which is not very convenient.

With the advent of powerful high-voltage transistors and diodes, welding inverters... Their main advantages: small dimensions, smooth adjustment of the welding current, overload protection. The weight of a welding inverter with a current of up to 250 Amperes is only a few kilograms.

Principle of operation welding inverter is clear from the following block diagram:

An alternating mains voltage of 220 V is supplied to a transformer-free rectifier and a filter (1), which forms a constant voltage of 310 V. This voltage feeds a powerful output stage (2). Pulses with a frequency of 40-70 kHz from a generator (3) are fed to the input of this powerful output stage. The amplified pulses are fed to a pulse transformer (4) and then to a powerful rectifier (5) to which the welding terminals are connected. The control and overload protection unit (6) regulates the welding current and protects.

Because inverter operates at frequencies of 40-70 kHz and higher, and not at a frequency of 50 Hz, like a conventional welder, the dimensions and weight of its pulse transformer are ten times less than that of a conventional 50 Hz welding transformer. And the presence of an electronic control circuit allows you to smoothly regulate the welding current and provide effective overload protection.

Let's look at a specific example.

Inverter stopped cooking.The fan is running, the indicator is on, and the arc does not appear.

This type of inverter is quite common. This model is called "Gerrard MMA 200»

We managed to find a circuit of the MMA 250 inverter, which turned out to be very similar and helped significantly in the repair. Its main difference from the desired scheme MMA 200:

The output stage has 3 field-effect transistors, connected in parallel, and the MMA 200 - by 2.
Output pulse transformer 3, and at MMA 200 - only 2.

The rest of the scheme is identical.

At the beginning of the article, a description of the structural diagram of the welding inverter is given. It is clear from this description that welding inverter, this is a powerful switching power supply with an open-circuit voltage of about 55 V, which is necessary for the occurrence of a welding arc, as well as an adjustable welding current, in this case, up to 200 A. The pulse generator is made on a U2 microcircuit of the SG3525AN type, which has two outputs for control of subsequent amplifiers. The generator U2 itself is controlled through an operational amplifier U1 of the CA 3140 type. This circuit regulates the duty cycle of the generator pulses and thus the value of the output current set by the current control resistor brought out to the front panel.

From the output of the generator, the pulses are fed to a preamplifier made of bipolar transistors Q6 - Q9 and field workers Q22 - Q24 operating on a transformer T3. This transformer has 4 output windings which, through the formers, supply pulses to 4 arms of the output stage assembled in a bridge circuit. In each shoulder there are two or three powerful field workers in parallel. In the MMA 200 scheme - two each, in the MMA - 250 scheme - three each. In my case, the MMA-200 has two field-effect transistors of the K2837 (2SK2837) type.

From the output stage, powerful pulses are fed to the rectifier through transformers T5, T6. The rectifier consists of two (MMA 200) or three (MMA 250) full-wave midpoint rectifier circuits. Their outputs are connected in parallel.

A feedback signal is supplied from the rectifier output through connectors X35 and X26.

Also, the feedback signal from the output stage through the current transformer T1 is fed to the overload protection circuit, made on the thyristor Q3 and transistors Q4 and Q5.

The output stage is powered by a mains voltage rectifier assembled on a VD70 diode bridge, C77-C79 capacitors and forming a voltage of 310 V.

To power low-voltage circuits, a separate switching power supply is used, made on transistors Q25, Q26 and transformer T2. This power supply generates a voltage of +25 V, from which +12 V is additionally formed through U10.

Let's go back to the repair. After opening the case, a visual inspection revealed a burnt capacitor 4.7 μF at 250 V.

This is one of the capacitors through which the output transformers are connected to the output stage on the field workers.

The capacitor has been replaced and the inverter is working. All voltages are normal. After a few days, the inverter stopped working again.

A detailed examination revealed two broken resistors in the gate circuit of the output transistors. Their nominal value is 6.8 ohms, in fact they are in the cliff.

All eight output field effect transistors were tested. As mentioned above, they are included two in each shoulder. Two shoulders, i.e. four field workers, out of order, their leads are short-circuited. With such a defect, high voltage from the drain circuits enters the gate circuits. Therefore, the input circuits were tested. Defective elements were also found there. This is a zener diode and a diode in the pulse shaping circuit at the inputs of the output transistors.

The check was carried out without soldering the parts by comparing the resistances between the same points of all four pulse shapers.

All other circuits were also tested up to the output terminals.

When checking the weekend field workers, all of them were soldered. The faulty ones, as mentioned above, turned out to be 4.

The first turn-on was done without any powerful field-effect transistors at all. With this turn on, the serviceability of all power supplies 310 V, 25 V, 12 V was checked. They are normal.

Voltage test points on the diagram:

Checking the 25V voltage on the board:

Checking the 12V voltage on the board:

After that, the pulses at the outputs of the pulse generator and at the outputs of the shapers were checked.

Pulses at the output of the shapers, in front of the powerful field-effect transistors:

Then all the rectifier diodes were checked for leakage. Since they are connected in parallel and a resistor is connected to the output, the leakage resistance was about 10 kΩ. When checking each individual diode, the leakage is more than 1 mΩ.

Further, it was decided to assemble the output stage on four field-effect transistors, placing not two, but one transistor in each arm. Firstly, the risk of failure of the output transistors, although it is minimized by checking all other circuits and the operation of power supplies, still remains after such a malfunction. In addition, it can be assumed that if there are two transistors in the arm, then the output current is up to 200 A (MMA 200), if there are three transistors, then the output current is up to 250 A, and if there is one transistor each, then the current may well reach 80 A. This means that when installing one transistor in the shoulder, you can cook with electrodes up to 2 mm.

It was decided to make the first control short-term switching on in the XX mode through a 2.2 kW boiler. This can minimize the consequences of an accident if, nevertheless, some kind of malfunction was missed. In this case, the voltage at the terminals was measured:

Everything works fine. Only the feedback and protection circuits were not tested. But the signals of these circuits appear only when there is a significant output current.

Since the switching on was normal, the output voltage is also within the normal range, we remove the series-connected boiler and turn on the welding directly to the network. Check the output voltage again. It is slightly higher and within 55 V. This is quite normal.

We try to cook for a short time, while observing the operation of the feedback circuit. The result of the operation of the feedback circuit will be a change in the duration of the generator pulses, which we will observe at the inputs of the transistors of the output stages.

When the load current changes, they change. This means the circuit is working correctly.

But the pulses in the presence of a welding arc. It can be seen that their duration has changed:

Missing output transistors can be purchased and replaced.

The article material is duplicated on video:

ARC-200 welder Chinese. The scheme is 90% the same as the SAI-200.
malfunction: cooks, the current is adjustable, you can burn half of the 4Ki electrode. but when the electrode is torn off, the protection is triggered, after that it starts to work constantly at any current. Check the snubers, diode drivers, the protection was rude - no use.
The block diagram is as follows:

Can anyone come across this?

Replacing the top board eliminated the cause

your block diagram has the wrong welding output voltage. 28 volts do not exist with these devices. Usually 56-72 volts

I would like to find the reason if it is in the board. Usually 50-80 at XX, and when naked. 200A can and 28v What is written on the diagram, just infa taken from the nameplate of the inverter. Here is a photo

Yes, the layout is different, just everything was blinded on one board, except for the control board, but the circuit is basically the same.

Sketched the diagram, maybe someone will come in handy.

[quote = ”vasa”] I advise you to solder everything

If it does not help, carefully check the harness near CA3140, SG3525

Then try to replace CA3140, SG3525 [/ quote]
Everything that is poorly soldered in appearance is soldered, replaced, just in case, CA3140; KA3525 has a good response to the load, there is no point in replacing it.

And how did the device work before the breakdown?

Make sure that there are no pulsations in the power supply of the control unit.

Become a 9-pin PWM oscilloscope and check the absence of "jumps" in the OS signal at various current assignments

5

som 12 Jan 2013

2

morgmail 12 Jan 2013

If you just adjust the throttle, and so, good old three-stage Chinese.

2

70rufs 12 Jan 2013

som 12 Jan 2013

Tried to make it work in the cold

70rufs 12 Jan 2013

1

morgmail 13 Jan 2013

Bumped into somewhere on the forum. They put such, but the electronics engineers scare the sudden death of the device. Also, not every welder can adjust the current during welding. On the MS. grandfather I installed a drive from a remote surveillance camera on the device, which turns the spinner itself.

LamoBOT 13 Jan 2013

On such a ketase, you can. I did. But if you accidentally short-circuit one of the control wires with the welding ones, it can die. You can also find a regulator with a motor. These are used in some multimedia speaker systems, but the impedance must be at least roughly the same. Put two buttons - current up and current down (motor left-right).

2

tehsvar 13 Jan 2013

I want to make an external regulator, 3-4 meters

Do it, he won’t give a damn. A couple of dozen did so. No refunds. Only requests to deliver. We were the only ones who were so ingenious to put it in the firm. The simplest thing is to put the rezyuk with switching back and forth.

a sinful thing, I thought: did the cunning Chinese have a temperature sensor built into it?

No, but the elements are not defense, and therefore I was faced with the fact that electronics do not work in the cold. Sometimes he healed, but in the cold you can't measure for a long time, what's wrong where. So it happens.

som 14 Jan 2013

Why is there 3 terminals in the potentiometer? Rezyuk to select the resistance at the end points of the flywheel? Which switch do you recommend (2 positions, 9 terminals)?

2

tehsvar 15 Jan 2013

1

som 27 Jan 2013

Is this okay?

regular Kiloomnik, and this one and a half Kilooma. Deadly?
The connection diagram is this ??

som 27 Jan 2013

Do you have an opinion? about the previous post

morgmail Jan 27, 2013

tehsvar 06 Feb 2013

som 06 Feb 2013

You got the meaning, but that you don't have 1 kOhm. I just don't know how it will work with 1.5.

OGS repairmen said it was not fatal. It will simply give a strong drop in the SV current. Although I would rather answer with the words “Dimona” from “Nasha Rasha”: - Slavik. Even I o..u. I will look for an "omnic".

3

som 06 Feb 2013

You got the meaning, but that you don't have 1 kOhm. I just don't know how it will work with 1.5.

Here's what I bought from a radio botany store:

The switch reads 3 Amperes. 125 VAC of some kind.
Soviet stereo jack will look trump on the welder's panel! I'll paint on the headphone icon above it. By the way, the saleswoman gave me lectures that THIS “dad” will not fit THIS “mom” and, in general, how 3 fingers can go into 5 holes. Well, in the style of a lieutenant, I squeezed out - that I grew up in a country that produced EVERYTHING with such connectors and. sometimes I inserted 1 finger into three holes for some

Isperyanc 11 Feb 2013

1

p0tap4ik 17 Mar 2013

Gentlemen, I looked at the “giblets” and thought, but you can, in theory, put a digital display of the current strength.

som 18 Mar 2013

It is better to replace the toggle switch with a relay that would switch the contacts simply when the dad is connected to the mom, for this, the dad must have a pair of short-circuited contacts through which the power will go to the relay coil. And the music connector is complete rubbish.

I'm a pretty good relay myself. Musical "five" from those available in the store is the most relevant. There was a 4-finger connector for a professional microphone - it was too big in size. How many amperes goes through the rheostat?

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 have compact dimensions 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. ...

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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.

The repair of inverter welding machines also differs in the following feature: there are often cases when it is impossible or difficult to determine the faulty element by the nature of the malfunction and you have to consistently check all the components of the circuit. From all of the above, it follows that for a successful self-repair, knowledge in electronics (at least at the initial, basic level) and little skills in working with electrical circuits are required. In the absence of these, do-it-yourself repairs can result in a waste of energy, time and even lead to additional malfunctions.

An instruction is included with each unit, which contains a complete list of possible malfunctions and the corresponding solutions to the problems that have arisen. Therefore, before doing anything, you should familiarize yourself with the recommendations of the manufacturer of the inverter.

All malfunctions of welding inverters of any type (household, professional, industrial) can be divided into the following groups:

caused by the wrong choice of the welding operating mode;

associated with the failure or malfunction of the electronic components of the device.

In any case, the welding process is difficult or impossible. Several factors can cause a problem with the machine. They should be identified sequentially, moving from a simple action (operation) to a more complex one. If all the recommended checks are completed, but normal operation of the welding machine has not been restored, then there is a high probability of a malfunction of the inverter module electrical circuit. The main reasons for the failure of an electronic circuit are:

Ingress of moisture into the device - most often occurs due to precipitation (snow, rain).
Dust accumulated inside the housing interferes with the normal cooling of the electronic components. As a rule, most of the dust gets into the machine when it is used on construction sites. To prevent this from causing damage to the inverter, it must be cleaned periodically.
Failure to comply with the manufacturer's mode of continuity of welding work can also lead to failure of the inverter electronics as a result of its overheating.

Most often, malfunctions are associated with external factors, settings and errors in the operation of the inverter. The most typical situations:

The welding arc is unstable or the work is accompanied by excessive spatter of the electrode material. This occurs when the wrong choice of current, which must correspond to the diameter and type of the electrode, as well as the welding speed. The manufacturer of the electrodes indicates recommendations for the selection of the current strength on the packaging. In the absence of such information, it is worth using the simplest formula: apply 20–40 A per 1 mm of the electrode diameter. If the welding speed is reduced, the current should be reduced.

The welding electrode sticks to metal - this can be caused by several reasons. Most often this happens due to a too low supply voltage of the network to which the device is connected, and in the case of an inverter with the ability to work at a reduced voltage, the latter is reduced when the load is connected to a level lower than the specified minimum. Another possible reason is poor contact of the device modules in the panel sockets. It is eliminated by tightening the fasteners or tighter fixing of the inserts (boards). A voltage drop at the input of the device can be caused by the use of a power strip, whose wire has a cross section of less than 2.5 mm 2, which also leads to a decrease in the supply voltage of the inverter during welding. Also, the reason may be too long an extension cord (with an extension wire length of more than 40 m, efficient operation is generally impossible due to very large losses in the supply circuit). Sticking can occur due to the burning or oxidation of contacts in the power supply circuit, which also leads to a significant "sinking" of the voltage. This problem can also manifest itself in the case of poor preparation of the products to be welded (the oxide film significantly worsens the contact of the part with the electrode).

The inverter is on, its indicators are on, but no welding. Most often this occurs due to overheating of the device, when the glow of the control indicator or lamp (if available) is hardly noticeable, and the inverter does not have a sound signal. The second reason is spontaneous disconnection of welding cables or their breakage (damage).

Turning off the mains voltage during welding - an incorrectly selected circuit breaker is installed in the electrical panel. This device must be rated for currents up to 25 A.

The inverter does not turn on - low voltage in the network, insufficient for the operation of the device.

Stopping the operation of the inverter during prolonged welding - most likely the temperature protection has tripped, which is not a malfunction. After a pause of 20-30 minutes, welding can be resumed.

Serious damage to the inverter module may be indicated by the smell of burning or smoke coming from the casing. In this case, it is better to seek help from service specialists. Do-it-yourself repair of welding inverters requires certain skills and knowledge.To identify and eliminate the cause of the malfunction, the body of the device is opened and its filling is visually inspected. Sometimes the whole point is only in poor-quality soldering of parts, wires, other contacts on the circuit boards, and it is enough to re-solder them to make the device work. At first, they try to identify damaged parts visually - they may be cracked, have a darkened case or pins burned out on the board, electrolytic capacitors will be swollen at the top. All identified faulty elements are soldered and replaced with the same or similar ones with suitable characteristics. The selection is made according to the markings on the case or according to tables. When soldering parts, the use of a soldering iron with suction will provide maximum speed and convenience of work. Image - DIY repair arc 200

If the visual inspection did not bring any result, then proceed to ringing (testing) the parts using an ohmmeter or multimeter. The most vulnerable elements of inverter modules are transistors. Therefore, the repair of the apparatus usually begins with their inspection and verification.Power transistors rarely fail by themselves - as a rule, this is preceded by a failure of the elements of the "swinging" circuit (driver), the details of which are checked first. In the same way, by means of the tester, they call the rest of the board elements.

On the board, it is necessary to check the condition of all printed conductors for the absence of breaks and burns. The burnt areas are removed and the jumpers are soldered, as in the case of breaks, with a PEL wire (with a cross section corresponding to the board conductor). You should also check and, if necessary, clean (with a white eraser) the contacts of all connectors in the device.

Rectifiers (input and output), which are conventional diode bridges mounted on a heatsink, are considered to be quite reliable components of inverters. But sometimes they fail. It is most convenient to check the diode bridge after unsoldering the wires from it and removing it from the board. If the entire group of diodes rings for a short time, then you should look for a broken (faulty) diode.

The key management board is checked last. In the inverter module, this is the most complex element and the operation of all other components of the apparatus depends on its functioning. The final stage in the repair of the inverter welding device should be to check the presence of control signals coming to the busbars of the gates of the key block. Diagnose this signal using an oscilloscope.

In cases that are unclear and more complex than those described above, the intervention of specialists will be required. Trying to fix the malfunction yourself is not worth it, especially when the inverter is under warranty.

Video (click to play).