DIY repair of a welding inverter mma 250

Compound:
master oscillator - uc3846dw, tl082 and 2 pcs. tl084i, buildup - ao4606, keys - gw45hf60wd, output rectifier - stth60w03cw
They brought it without any signs of life. The check revealed a dead roll at 12 V (exploded) and 4N90C. I changed it, I turn it on. Power supply +24, +12 and -15, everything is stable, there is a saw on the master, the output is silent. I further check the elements for deadness - the diodes are alive, I have not checked the keys yet, there are two small scarves in the key chains on which in the middle there are 2 either a dinistor or a zener diode. in general, I did not find data in the tyrnete. Marking BM1238 and BM1243. Maybe someone can tell me? In the board, one side does not ring at all, the other - as if a capacitor is charged, and then infinity. It should be?

It would not hurt to have a diagram from him, but I can't find something. Found a couple of similar ones, but a little not that. If there is, please share. A device with a vertical arrangement of connectors.

is there a processor? I did not indicate it in the composition, but I cannot understand from the pictures
Check the keys. I personally solder each transistor and check it. It's hard to find a defect there.

Radist morze, BMxxxx? These are bidirectional zener diodes in IGBT gates at 15v, you can set both 15v and 18v. Download information on SMAJxxxxx and make sure. Yes, in principle, any circuit with such a set of circuits as in Gerrard Edon mma-250 is confirmation of this. the numbering will be different.

REKKA, but where does the processor come from? This is not a 20-30 mowing machine.
Irina Slava, thanks for the comprehensive answer. I watched some kind of circuit, and I also came to the conclusion that these are zener diodes, only in that circuit they are inversely connected in series. And I already know about numbering. It's just that the composition is slightly different. Apparently, here is 3846 with external excitation, and this generator is on tl082. After it there are 2 pieces of tl084i, and then 3846. And in that diagram, everything is on tl084.
found a broken diode. one of the counter-parallel included in the tl082 strapping. Now I will look for Old and Replacement.

the diode was in a semi-torn state, if you press it down with a probe, it rings. on the board at first it also called, then stopped. I changed it, but it's no use.

Radist morze, the network has a MMA ZX7-225 scheme, here it is. close to required or ZX7200IGBT.

this scheme is suitable for my Dnieper, it is also three-story. and this is a stranger. " e-don ”single board. Well I write above that with a vertical arrangement of bayonet connectors.

REKKA, what have the keys to do with it when the control impulses do not come from the micro? on 3846 there is a saw on leg 8, there is an impulse on leg 10, and the exit is dead.

by the way, I thought that 3846 was dead, replaced - the same thing. tl082 also replaced, there is no sense either. I sin on tl084i, but I don't have them

here the ZX-7 diagram is similar, but not completely identical in details.

REKKA, at first I also thought that dead keys can plant an impulse, but there are still field workers between the microra and the keys. Yes, and I soldered the keys, the effect is the same. on the other hand, broken keys will not send an impulse. there is a trance between the field workers and the igbt. No, there is a problem somewhere in the generator.

I think I get it. The blown up stub microcircuit is most likely 15 volts, not 12. I was confused by someone's post on the Internet that the opamp can have an oblique power supply. Having looked through several schemes, I did not see a single one where it would be +12, -15 and +24. Everywhere food is +15, -15, +24. I don't have any 15 V rolls now, I need to connect from the laboratory power supply unit. I will unsubscribe based on the results. Perhaps later, because the lights are turned off.

Guys, I was right! I changed the roll 12 to 15 and the impulses started running. And why didn't anyone correct me right away? I wrote at the beginning. I am assembling the apparatus. I'll try to cook and unsubscribe.

The sparkler is working, but my opinion about it is a shitty device. In principle, it cannot give out the declared current of 250 amperes, since the keys, working in pairs, are at 45 amperes. in total, each shoulder is also 45 amperes. The datasheet says that this is the maximum current.Suppose that in the impulse mode it is two times more, totaling 90 each arm, which means 180 the entire bridge. The question is, what 250 amperes can we talk about? The Chinese apparatus is the Chinese current. I tried to cook it. My “Dnipro MMA-200” cooks better and produces more current. This is not an advertisement for Dnipro, this is just for comparison. Verdict - don't buy gowns.

- the bridge pumps the primary. in the secondary - its own current and voltage. and the number of turns in the secondary.

KRAB, sorry, I figured it out last night too. I came here to correct the message, and here is a new post 🙂 Outstripped!

but all the same, three-story buildings are better, in my opinion.

I put 110 amperes on edon, I cook a profile pipe. Shit seam. I bet on my own - a completely different matter. In general, I cook it with my apparatus at 75-100 amperes, depending on the place of the seam. And edon on the 110th “shelf” does not warm up, but I am not talking about the rib at all.

You can, of course, write off everything on the nonlinear dependence of the regulator in edon. There is a digital scale in mine, so I don't bother with the position of the regulator and the discrepancy between its nonlinear characteristics and markings on the body. Although the scale can also be incorrectly set if someone clocked it.

So your “Dnipro mma-200” is a 100% Chinese device, don't look at the name,

If you already want to have a purely native inverter, take Paton, this is a Ukrainian assembly

tynalex, the Ukrainian assembly will now take almost nothing, they do not bring them to us. and according to your first link - an American iPhone is also made in China. Yellow-horned production is cheaper. Norwegian seiners take the caught fish to China for processing, and then the finished products are transported to Norway. Estimate how many man-hours the crew puffs, how much fuel, but it is still cheaper for them, because fish processing is very expensive in Norway. I once wanted to make a bungle for myself, but in terms of details it came out about two thousand hryvnias, and I didn’t take that into account, but I simply didn’t find something and didn’t know the prices. And it still needs to be done. As a result, he rummaged around and bought himself a factory one, in a suitcase, and for another 970 hryvnia, it seems. The delivery cost seems to be 1040. And they are already boiled-overcooked. recently the non-stick has stopped working, but that's another topic. And in general, this topic has been closed for two days already, we will not throw a flood.

These devices have been known for a long time and there are 1: 1 schemes for them (I have for a long time in the folder

) - already laid out. search by the words “Chinese mini-bridge”.

Tell me what kind of pribluda as a transistor is on this photo and what is its marking?

sp700, and here a little higher a link to the diagram was laid out. Sob-but a transistor is a transistor.

Hello, readers of the site I read a lot here about the repair of various CAs, and now I want to share my experience myself. They brought in that week for repair a welding inverter for arc welding "Hero of MMA MINI-250".

The device is made using IGBT technology or (semi-bridge).

With a complaint from the owner that the electrode sticks and does not want to weld. After plugging into the network
and attempts to weld the part, nothing worked. And after changing the welding current to a higher one, the welding started to smoke and heard an electric crack. The owner said that the cause of the breakdown was the wrong choice of welding current for the electrode.

Attention: all work on the repair and restoration of the welding inverter, you perform at your own peril and risk.

After disassembly, it was decided to unscrew and check the power supply unit.

A burnt-out 150 ohm 10W resistor was found.

The 100V 35A diode bridge and the 24 35A relay turned out to be working.

And in the power supply unit, a swollen capacitor of 470 μF x 450 V was found, which was replaced.

Next, we check the top board.

1. Power key driver. (everything that is possible on this scarf is checked, the resistance should be no more than 10 ohms).
2. Power keys.
3. Power supply 24 V. (the K2611 transistor or its analog and its body kit are checked, see the photo).
4. Master generator. (all field-effect transistors are checked, you can check by turning on the welding when turning on and off, the generator should squeak).

The IRG4PC50UD keys or its analogs are installed here. With a multimeter in the diode test mode, you need to ring the legs of the transistor “E” and “C” in one direction they should ring out, and in the other direction they should not ring out the transistor needs to be discharged (close all the legs).On legs “G” and “E”, the resistance should be infinite, regardless of polarity.

Next, you need to apply to the leg “G” - “+” and to “E” “-” 12 volts DC. and ring the legs “C” and “E” they should ring. Next, you need to remove the charge from the transistor (close the legs). Legs “C” and “E” should have infinite resistance. If all these conditions are met, then the transistor is working, and so you need to check all the transistors.

Diodes break very rarely, but if one breaks, then after itself it breaks all the others. An approximate diagram of this MMA-250 welding is here (not complete). After all the defective parts have been replaced, we assemble the welder in reverse order and check for operability. Article author 4ei3

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 supplies 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 works 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, after all, 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:

Inverter welding machines are gaining more and more popularity among master welders due to their compact size, low weight and reasonable prices. Like any other equipment, these devices can fail due to improper operation or due to design flaws. In some cases, the repair of inverter welding machines can be carried out independently by examining the inverter device, but there are breakdowns that are eliminated only at the service center.

Welding inverters, depending on the models, operate both from a household electrical network (220 V) and from a three-phase (380 V). The only thing to consider when connecting the device to a household network is its power consumption. If it exceeds the capabilities of the wiring, then the unit will not work with a sagging network.

So, the following main modules are included in the device of an inverter welding machine.

Just like diodes, transistors are installed on radiators for better heat dissipation from them. To protect the transistor unit from voltage surges, an RC filter is installed in front of it.

Below is a diagram that clearly shows the principle of operation of the welding inverter.

So, the principle of operation of this module of the welding machine is as follows. The primary rectifier of the inverter is supplied with voltage from the household electrical network or from generators, gasoline or diesel. The incoming current is alternating, but passing through the diode block, becomes permanent... The rectified current is fed to the inverter, where it is converted back to alternating current, but with changed frequency characteristics, that is, it becomes high-frequency. Further, the high-frequency voltage is reduced by a transformer to 60-70 V with a simultaneous increase in the current strength. At the next stage, the current again enters the rectifier, where it is converted to DC, after which it is supplied to the output terminals of the unit. All current conversions controlled by a microprocessor control unit.

Modern inverters, especially those based on the IGBT module, are quite demanding on the rules of operation. This is explained by the fact that when the unit is operating, its internal modules give off a lot of heat... Although both radiators and a fan are used to remove heat from power units and electronic boards, these measures are sometimes not enough, especially in inexpensive units. Therefore, you need to strictly follow the rules that are indicated in the instructions for the device, implying periodic shutdown of the installation for cooling.

This rule is usually referred to as the “Duty Cycle” (Duty Cycle), which is measured as a percentage.Not observing the PV, overheating of the main units of the apparatus occurs and their failure occurs. If this happens with a new unit, then this breakdown is not subject to warranty repair.

Also, if the inverter welding machine is working in dusty rooms, dust settles on its radiators and interferes with normal heat transfer, which inevitably leads to overheating and breakdown of electrical components. If it is impossible to get rid of the presence of dust in the air, it is necessary to open the inverter case more often and clean all the components of the device from accumulated dirt.

But most often inverters fail when they work at low temperatures. Breakdowns occur due to the appearance of condensation on the heated control board, as a result of which a short circuit occurs between the parts of this electronic module.

A distinctive feature of inverters is the presence of an electronic control board, therefore, only a qualified specialist can diagnose and eliminate a malfunction in this unit.... In addition, diode bridges, transistor blocks, transformers and other parts of the electrical circuit of the apparatus can fail. To carry out diagnostics with your own hands, you need to have certain knowledge and skills in working with measuring instruments such as an oscilloscope and a multimeter.

From the above, it becomes clear that, without the necessary skills and knowledge, it is not recommended to start repairing the device, especially electronics. Otherwise, it can be completely disabled, and repairing the welding inverter will cost half the cost of a new unit.

As already mentioned, inverters fail due to external factors affecting the “vital” units of the apparatus. Also, malfunctions of the welding inverter can occur due to improper operation of the equipment or errors in its settings. The most common malfunctions or interruptions in inverter operation are as follows.

Very often, this breakdown is caused by faulty network cable apparatus. Therefore, first you need to remove the cover from the unit and ring each wire of the cable with a tester. But if everything is in order with the cable, then more serious diagnostics of the inverter will be required. Perhaps the problem lies in the standby power source of the device. The repair technique for the “duty room” using the example of a Resant brand inverter is shown in this video.

This malfunction can be caused by an incorrect setting of the amperage for a certain diameter of the electrode.

You should also consider and welding speed... The smaller it is, the lower the current value must be set on the control panel of the unit. In addition, to match the current strength to the diameter of the additive, you can use the table below.

If the welding current is not regulated, the cause may be breakdown of the regulator or violation of the contacts of the wires connected to it. It is necessary to remove the cover of the unit and check the reliability of the connection of the conductors, and, if necessary, ring the regulator with a multimeter. If everything is in order with him, then this breakdown can be caused by a short circuit in the inductor or a malfunction of the secondary transformer, which will need to be checked with a multimeter. If a malfunction is found in these modules, they must be replaced or rewound to a specialist.

Excessive power consumption, even when the device is not loaded, most often causes turn-to-turn closure in one of the transformers. In this case, you will not be able to repair them yourself. It is necessary to take the transformer to the master for rewinding.

This happens if the voltage drops in the network... To get rid of the sticking of the electrode to the parts to be welded, you will need to correctly select and set up the welding mode (according to the instructions for the device). Also, the voltage in the network may sag if the device is connected to an extension cord with a small wire cross-section (less than 2.5 mm 2).

It is not uncommon for a voltage drop that causes the electrode to stick when using a power strip that is too long. In this case, the problem is solved by connecting the inverter to the generator.