Small problem in high Amps SMPS power supply

[BGAmodz]

I'm sure tcmtech and I will be able to help a bit more, but YOU have the hard grind ahead.

Thanks this would be really nice from you guys

 

[BGAmodz]

So I gather you replaced the diode then went to power up, and !!!
back to basics again. Have a re-read of post #2.

I have totally forgot about this post , my bad , i will take this advices in consideration in the futur for sure .


So
While doing a little research i have found that the power IC witch is the PWM ic is responsible for driving the IGBTs , that are creating switched pulses witch are induced to a switching transformer , then this induced voltage is rectified by schottky diodes and dual diodes to be then delivered to the regulator that gives a stabilized dc voltage .

Now what i think is maybe with a bad soldering of the power IC ( because i have already removed it ) , and after having replaced the dual diode that i previously mentioned , the unit was working fine and suddenly the power IC was disconnected witch caused the shorts on the igbt and schottky /rectifying diodes .

BTW i have two transformers on the welder , a pulse transformer and a current transformer .

 

[tcmtech]

Unfortunately if you just killed one or more of the primary switching devices due to control board related problems the odds are going and buying a new machine may get you money and time ahead.

These cheap off brand inverter type machines are designed to be throw away units if they ever have anything more than a minor breakdown.

Believe me. I worked as a service tech on welders and plasma cutters for a local dealer and most any machine that is inverter power supply based is not worth the time and money to fix unless it's got a factory warranty taking the cost hit for you.

 

[BGAmodz]

I see , but the problem is that its not mine , i was assigned to repair this welder from a welders selling company , and its been 1 week they are waiting .
Anyways waiting for Rumpfy's opinion .

 

[BGAmodz]

I use a pair of back to back 24 volt transformers to isolate the control circuits when fault finding these things, but when you reach the point of full power testing, the isolating traffos have to go and then one is in the dark again. The current sensing is difficult to simulate.

Ok , can i test the primary side using an ac input of 24 V AC only ??

 

[rumpfy]

I understand your dilemma.
I think I have to say, that tcmtech and I would be of a similar mind.
I had an ESAB welder which was faulty and during reassembly, there was a short between the control circuit ground and the power mains earth. This took out a few diodes and was hard to work on so I hoped the customer would just go away. It took about 18 months for someone to start pressing me for a resolution. I found a couple of simple IC's were US and replaced them but while finally checking things, a puff of smoke came from the SG3525? control IC. I wasn't able to get a surface mount device so I opted for a DIP package and had to mount it end-on and glue it to the board. Connections were done between the IC and the PCB with 0.2 mm wire strand. I felt like I was working in swiss watch factory. Nevertheless, all was well in the end, and I tried out the welder with some 4 mm welding rods and it worked like a dream.
However, I have an 'italian job' which is the most idiotically complex double sided circuit board you could imagine; it is almost impossible to trace the circuit tracks. It has been in my shed for about 7 years and is going nowhere fast. A bolt came loose in this welder and blew the crap out of everything. I got as far as replacing all the big mosfets, but at the operating test stage, smoke comes from the guts of it and it is too dark to see what is what. I think the current control is at fault.
So, if you want to press on, you will certainly need the proper circuit diagram. You will also need to have an idea of the price/availability of the major semiconductors.
You will also need to consider that you may have an unforeseen disaster with the repairing.

So I think you need to consider the story to tell your customer. This would be something like;
" the design of this thing is rather complex as it is a high speed, high power, electronic circuit, and for faults in the high power section, these designs are almost impossible to repair, because of the possibility that some components MAY have been damaged as a result of the original fault. It may be possible to repair, but it is quite likely that within the warranty period, that another failure would occur and such a result would damage both of our reputations. If it is your wish to proceed with the repair, I cannot promise I will be successful, but my preferred approach is to advise you not to proceed any further. It is the case with modern manufacturing, that products are generally cheap to make and assemble, but they can often be uneconomical to repair "

I thank you for your confidence in me and sorry it is not of much help. Post 2 is worth looking again!

 

[BGAmodz]

Yes rumpfy , these situations are really hard for me as a beginner in professional repairs , i will never put my hands on hardware like this again , unless its something very feasible and affordable .

Thanks for your time .

 

[BGAmodz]

Hi guys again .

I got another job to do and unfortunately same thing happened again , right after replacing the shorted chopper circuit , the unit got them shorted again .

According to your experience what could be causing the shopper transistors to short ???

 

[rumpfy]

Is this one of those "Telwin Technica 141-161 "welders for which you supplied the handbook?
If not, you wont get far without the circuit diagram; and for me, making suggestions would be very iffy.I note on P 10 of the 'Technica' that they suggest a CRO is a useful repair tool. Do you have CRO?
On pages 11 to 15, they take you through a range of factors; just check these through and relate them to your unit.