Electronic welding machine in short circuit

[DisasterNow]

Hi, I have an electronic welder that no longer works. It turns on regularly, the green light works and so does the fan, but I have no voltage on the output. It should have about 80 volts at no load. Visually I don't notice any burnt components, but when I power the board via variac and a light bulb in series, there are moments in which I feel the fan speed drop and the light bulb lights up slightly, indicating that there is a short circuit on the board. I checked the temperature of the components, but I can't find anything with high temperatures. Do you have any advice for finding the short circuit? The card is very similar to this one, thanks.

[DisasterNow]

I add the electrical board diagram (not 100% identical, but almost the same)

[DisasterNow]

Maybe you can see it better in the PDF (it's from an inverter of the same brand, but I'd say that the PCB is almost identical)

[coppercone2]

its something on a heat sink if you cant find it

[DisasterNow]

The bulb dissipates the short circuit, so no protection fails and perhaps not even the faulty component. There are many heat sinks, is there a way to understand if it really depends on a heat sink? The board also has thermal control, but I believe only on one of the two heatsinks with 4 IGBTs. Thank you

[coppercone2]

Ok I am saying if you think there is a short circuit, but you can't find any hot parts, chances are its a part on a heat sink, or with a heavy ground plane.

For high voltage power boards you really want a thermal camera that can point you in the right direction. Usually bad welding machines have blown parts.

My broke welder had clear signs of burn damage. Did you check perhaps to inspect the parts with a mirror to look for a cracked transistor? They often blow a corner off or something like that and look mostly OK

This one looks really simple. You could replace every single part fairly cheap, its always an option


My hunch is something bad with parallel MOSFET. I would just buy a dozen on digikey and give it a shot replacing them all lol, for 20$ + thermal grease. Chances are it might be a cheap welder with counterfeit parts (suspicious this is from amazon) and you might improve the thing. Plus, its kinda safer then probing around those. And you can probe most of the diodes too.


With parallel mosfet it might be complicated to try to determine if one of em is acting up, their like $2.95 so is it worth it ?


A good machine would have factory made IGBT bricks for this purpose. Parallel FET is alot cheaper but yeah who knows what can happen there!



I can ensure you, that probing those FET near the heat sink while its running is perilous. If you wanna try to do something there, get a fluke insulated grabber hook, turn off the machine, make sure its safe, connect the hook, measure, and repeat for every single measurement. Probing there  while its on is the risky part for this machine. Those TO packages near BIG heat sinks are recipe for short circuit trouble

[DisasterNow]

Ok I am saying if you think there is a short circuit, but you can't find any hot parts, chances are its a part on a heat sink, or with a heavy ground plane.

For high voltage power boards you really want a thermal camera that can point you in the right direction. Usually bad welding machines have blown parts.

My broke welder had clear signs of burn damage. Did you check perhaps to inspect the parts with a mirror to look for a cracked transistor? They often blow a corner off or something like that and look mostly OK

This one looks really simple. You could replace every single part fairly cheap, its always an option


My hunch is something bad with parallel MOSFET. I would just buy a dozen on digikey and give it a shot replacing them all lol, for 20$ + thermal grease. Chances are it might be a cheap welder with counterfeit parts (suspicious this is from amazon) and you might improve the thing. Plus, its kinda safer then probing around those. And you can probe most of the diodes too.


With parallel mosfet it might be complicated to try to determine if one of em is acting up, their like $2.95 so is it worth it ?


A good machine would have factory made IGBT bricks for this purpose. Parallel FET is alot cheaper but yeah who knows what can happen there!



I can ensure you, that probing those FET near the heat sink while its running is perilous. If you wanna try to do something there, get a fluke insulated grabber hook, turn off the machine, make sure its safe, connect the hook, measure, and repeat for every single measurement. Probing there  while its on is the risky part for this machine. Those TO packages near BIG heat sinks are recipe for short circuit trouble

Thanks, it's very kind of you. I'm at work, tonight I'll reflect on your advice 

[DisasterNow]

My experience troubleshooting an inverter electronic welding machine board is that of a beginner.
There are few transistors, they don't seem to be shorted, but they should be desoldered for an accurate check. Then there are some power diodes (they seem ok) and 8 IGBT (soldered onto the circuit, it is difficult to verify if they are efficient).
Of course I could replace the power components, but first I wanted to understand where the short circuit was located; It's not easy because for many minutes it doesn't absorb any extra current, and when it happens the bulb disperses it without causing further damage.
In reality the welding machine is not a super cheap model, even if it is many years old, but it has not worked much. The model is EPS energi@130 (manufacturing company is eps-inverter.com).
When it was given to me as a gift, the electrode only produced a few sparks, in fact the output is zero volts (it should be 80 DC at no load).
I carried out the voltage check on the component side only with the probe cable that detects the temperature, while I carry out the measurements on the track side.
For now I have verified that on the large filter capacitors I regularly have 310 DC; the relay works; the fan works. On the gate of 4 mosfets I have a voltage, while at the moment I don't have any voltage on the gate of the other 4 mosfets, but I have to check better. The IGTBs are IRF P 460s.
I add some photos: secondary diode

[DisasterNow]

transformer area

[DisasterNow]

8 IGBT

[DisasterNow]

hybrid logic board (covered by a transparent protection)

[DisasterNow]

Track side (I scratched the transparent protection, otherwise it wouldn't conduct on the multimeter tip)
Note the fixing of the 3 large heat sinks, with rivets...

[odemiriz]

If the welder powers on regularly (meaning green led on and no error led), primary switches - mosfets or IGBTs - are fine. You should first check output diodes with a multimeter. If there is a short there, you need to change the faulty ones. If not most likely you have problem with control board. Check the aux power for the control section.

[DisasterNow]

If the welder powers on regularly (meaning green led on and no error led), primary switches - mosfets or IGBTs - are fine. You should first check output diodes with a multimeter. If there is a short there, you need to change the faulty ones. If not most likely you have problem with control board. Check the aux power for the control section.

Yes, the welder turns on regularly, the fan turns and the green light is on; the yellow light does not come on (not even when the bulb indicates a slight short circuit). The output diodes (BYV52) verified in the diode test (on the board), would appear to be ok. I haven't yet done accurate voltage and signal tests in the control part, on the gate of 4 mosfets I have a voltage, while on the other 4 gates I have a zero voltage, but from the diagram it seems to me that it refers to the ground so maybe ok. The resistors and diodes between T4 and the gate seem ok. I don't understand what it is that doesn't allow the current to reach the output.
When the light bulb signals me the short circuit (only occasionally while the welder is running idle), I then lower the variac below 200AC and the short circuit disappears. I almost want to let him continue to see if he smokes anything, but I don't want to do any more damage. I still have to check better, but I had the feeling that by leaving the current regulator towards the minimum, the short circuit is more frequent, while if I raise the potentiometer towards the maximum (130 A), it doesn't signal any short circuit, but I have to do further tests . However, the output always remains at zero DC.

Thank you

[coppercone2]

well if the current is not reaching output that means the bridge is stuck or fried or control is fried. is the control card making a wave form into the gate of the transistors?

[DisasterNow]

well if the current is not reaching output that means the bridge is stuck or fried or control is fried. is the control card making a wave form into the gate of the transistors?

I think it's quite difficult for me to understand this fault. I have attached part of the diagram where I took some measurements. In the moments WITHOUT a short circuit, at the input of TR4 I have the right voltage (13.7v); at the output I have about 18/20v, which arrive at the gates of MF1-2-3-4. On the other output of TR4 I have the ground reference, which continued up to the gate of MF5-6-7-8.
During short moments, the output voltage from TR4 to MF1-2-3-4 alternates from 20 to 120 v!, and the input of TR4 drops from approximately 13.7 to 10 v. I also saw that the yellow LED lights up in moments of short circuit.
In the diagram I see that they distinguish between two types of mass (one has the symbol F). However, I see that there is continuity between these two masses on the PCB.
Thank you