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KL MMA160 inverter igbt arc welding machine does not weld although it gives an appropriate value of

Bazİstasyonu

Aug 6, 2022
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The output of the KL MMA 160 inverter igbt arc welding machine is 52 Volts and as it should be.

The fan is also working.

4 High-Speed Switching Diodes (1N 4148 5T) diodes exploded on the Transformer Rectifier circuit card of the machine, I replaced them with new ones, but it still does not weld.

It still only sparks when the electrode hits the metal, but it doesn't weld. The same problem persists when I increase the amps by turning the potentiometer up.

All elements on the AC rectifier curciut card of the machine are solid, namely capacitors and the resistors connected to them, diodes, relay, optocoupler, NTC and PTC.

The rectifier diodes(Output diodes) and IGBTs are also solid.

Since I couldn't understand what the problem was in the machine, I checked all the elements one by one.

I could not understand the reason why the machine does not weld when there is no problem in the cooling fan part, additionally the output voltage of the machine is correct (at a constant value and between 50 V -70 V at the required voltage).

In general, in which part of the machine and in which electronic components should I look for and error considering all this situation?

The diodes I changed are on the Transformer Rectifier floor:

5bf221d7-be2e-4f9d-85d1-a7a1520e8641-jpg.358542



Pictures of the machine:

be38ba80-6287-48f0-856e-3d7d590d65c5-jpg.358543



dc373bc8-0485-401c-a7b7-e29784d3e868-jpg.358544
 

Martaine2005

May 12, 2015
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Sounds like the voltage is present but not enough current available.
What happens to the voltage when you get an arc/spark (under load). Does it fall drastically?


Martin
 

Bazİstasyonu

Aug 6, 2022
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Sounds like the voltage is present but not enough current available.
What happens to the voltage when you get an arc/spark (under load). Does it fall drastically?


Martin
I do not have equipments to measure it while welding happens. What can you suggest me to search for in the device circuit for a possible repair attempt?
 

Martaine2005

May 12, 2015
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As I don’t know much about inverters, others here do, I would wait for assistance from them.
But generally a bad connection could cause the voltage to drop under load. If the diodes exploded, it must have drawn a lot of current. Possibly a PCB track has melted or gone open circuit.
But wait for somebody else with knowledge of inverters to chime in.


Martin
 

kellys_eye

Jun 25, 2010
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Are the diodes you replaced inserted in the correct orientation? Diodes don't just 'explode' without good cause and something else has quite likely gone wrong that's yet to be identified. Show the area with the blown diodes in close-up plus show the rear of the board where they are situated.

How did you identify the diodes as 1N4148's? Do you have a schematic for the unit?

I'd suggest you also give the boards a thorough clean using IPA - the crud on the board surface may be conductive......
 

Bluejets

Oct 5, 2014
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I count 5 diodes adjacent to eachother...think you'll find one would possibly be a zener.

Without more detail, hard to say.

Wouldn't expect to see 1N4148 as rectifiers there though.
 

kellys_eye

Jun 25, 2010
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I repaired a 3kW charger/inverter a while ago that used 1N4148's as a bridge rectifier to monitor line voltage (via a low voltage transformer secondary) - one of the diode shad gone o/c and the resultant voltage caused the output voltage of the inverter to be wrong.

The images show a transformer but I can't determine if it's SMPS or 'regular' (not that it makes much difference given the high speed switching the 1N4148's are capable of) and the circuitry does look as if it will generate a signal based on whatever the transformer is outputting/monitoring. We need to see how the transformer is connected (input and output) plus a closer look at that adjacent transistor...
 
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