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Welder repair help

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Buellboy

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Hello all, I hope someone can help with this as it has been costing me sleep and sanity...
I have an inverter tig welder that had a capacitor blow on one of the boards, I think the main power supply board but not sure since there is no info around about these Chinese welders. So I replaced the capacitor with an identical one and now I blow MOSFETs and resistors on the high frequency board. Any idea what might be going on? I don't think pictures would help but I'll upload some in a bit.
I added some pics... 1st 2 are of the board that keeps blowing mosfets and resistors. 2nd is of the main power supply board. Here's how it laid out...
https://www.electro-tech-online.com/custompdfs/2010/09/weldingpowersupplies-an.pdf (the gate drive diagram)

Thank you for your help
 

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Hello all, I hope someone can help with this as it has been costing me sleep and sanity...
I have an inverter tig welder that had a capacitor blow on one of the boards, I think the main power supply board but not sure since there is no info around about these Chinese welders. So I replaced the capacitor with an identical one and now I blow MOSFETs and resistors on the high frequency board. Any idea what might be going on? I don't think pictures would help but I'll upload some in a bit.
I added some pics... 1st 2 are of the board that keeps blowing mosfets and resistors. 2nd is of the main power supply board. Here's how it laid out...
https://www.electro-tech-online.com/custompdfs/2010/09/weldingpowersupplies-an-1.pdf (the gate drive diagram)

Thank you for your help

Maybe the capacitor went with a few other parts too...

Which capacitor blew? I assume it is the big black one that is the replacement capacitor in the 3rd pic?
 
Yes, it was the big black capacitor. When it blew, I noticed that one of the resistors on the hi freq board was blown too. I repaced it, and the machine lit up the o/c light and did nothing else. I assume it was reading too low a voltage. After investigating the mosfets, I found one that was shorted. Only after replacing that one did the welder stop lighting the o/c warning, and start blowing resistors and mosfets in spectacular explosions.
 
Is there any chance of you making a circuit diagram of the power supply?

Big caps don't usually blow, maybe the bridge rectifier has gone.
 
I never thought to check the bridge rectifier. Thanks for the tip. I will check it when I get hom from work.
Another thought... Some moron (me) read the resistor incorrectly and put in a higher value than intended. Am I correct in thinking that this would change the timing of the mosfet, and allow 2 opposite firing mosfets to fire at the same time, thus overpowering and then blowing them? Just a thought.
 
I never thought to check the bridge rectifier. Thanks for the tip. I will check it when I get hom from work.
Another thought... Some moron (me) read the resistor incorrectly and put in a higher value than intended. Am I correct in thinking that this would change the timing of the mosfet, and allow 2 opposite firing mosfets to fire at the same time, thus overpowering and then blowing them? Just a thought.

It all depends what type of circuit the resistor is in. It could be a mosfet gate resistor, but most likely it is for the timing of a frequency(on the high freq board).

I hope you still have that burned out resistor!:p

I wonder if any other capacitors could be damaged/bad too.
Hopefully, no chips or sensitive circuits have been harmed.
 
The bridge rectifiers check out fine. I pulled all the mosfets and gate resistors to check them out. A few of each were dead. Just awaiting a shipment from digikey to reassemble and hopefully not blow anything else. Everything on the power supply pcb seems to be ok...
 
How did you make out with your repair? I have the same power control board problem on my Longevity LS-200P. I "purchased" a replacement board with caps- the 30 amp relay had blown apart. I then found both rectifiers are failed too. I just received my KBPC 5010 rectifiers to put in. I am using a little circuit breaker to "diagnose" the system- but hope that it will power up. I didn't find any transistors failed yet. I'm hoping not to do component replacement on those boards- as the heat sink all needs to come out with a gagillion connections.
-Peter
 
Hi Peter,
I stumbled upon a yahoo group dedicated to the owners of chinese welders. A gent from Longevity named Eric has been most helpful. I finally have the schematics I've been scouring the web for. (For months). I have repaired the inverter board and can now weld again. Turns out the problem was a zener diode that I couldn't read. I used a 15 volt instead of a 5 volt and that was the cause of the machine not working. The original problem persists though...Every time I used the high frequency start, I blow out MOSFETS on the inverter board. I'm stumped. The circuit is dead simple...the inverter board feeds 100khz 350vac to a capacitor and transformer. The secondary side has voltage doublers and a spark gap. I can't find fault with any of the componants. I thought for sure the transformer was shorted, causing the FETS to overload and blow. But it seems fine. Don't know what else would cause the FETS to instantly self destruct the second I pull the trigger for the HF start.

Colin
 
Hi Peter,
I stumbled upon a yahoo group dedicated to the owners of chinese welders. A gent from Longevity named Eric has been most helpful. I finally have the schematics I've been scouring the web for. (For months). I have repaired the inverter board and can now weld again. Turns out the problem was a zener diode that I couldn't read. I used a 15 volt instead of a 5 volt and that was the cause of the machine not working. The original problem persists though...Every time I used the high frequency start, I blow out MOSFETS on the inverter board. I'm stumped. The circuit is dead simple...the inverter board feeds 100khz 350vac to a capacitor and transformer. The secondary side has voltage doublers and a spark gap. I can't find fault with any of the componants. I thought for sure the transformer was shorted, causing the FETS to overload and blow. But it seems fine. Don't know what else would cause the FETS to instantly self destruct the second I pull the trigger for the HF start.

Colin

actually when the mosfets got fried, the transistors/chips(?) that drive the mosfets might be fried too from overcurrent hence burning out the gate resistors. If the drivers have gone short, the MOSFETs will blow up, only if the MOSFETs are in a bridge-configuration. So I would check the transistors that drive the mosfets. However in the 2nd pic there seems to be no driver transistors, and that makes me assume the mosfets are driven via the small daughter-board with the diodes, high-freq. transformer, and resistors. I haven't seen the circuit yet, so I am a little unsure of what the problem could be.

So if you could post a pic of the circuit, that would be nice.

Also, next time you want to fire up the welder, use a 100W lightbulb in series with the welder, to keep it from self-destructing again ;)
 
The driver circuit is isolated by the transformer you saw on the daughter board. Aside from a few blown resistors and zeners that I've replaced, the driver is ok and functioning as it should. (verified by scope) The Welder produces the proper open voltage and current both ac and dc. The problem is with the HF start. I got a new (used)HF transformer, and it produces identical waves on the scope as the old one. So either both are fried, or the transformer is not the problem. (I am sending a high frequency square wave from a function generator)
Do you mean put a 100 watt bulb in series on the 340 vdc line to the HF transformer? Won't this blow the bulb?

I'll post some more pics when I get home...



How do you post pics or attach files?
 
Last edited:
How do you post pics or attach files?


Easy, click Go Advance at the bottom of the quick reply box.

Then scroll down any you will see Manage Attachments, click that and it will put you into a window to upload attachments (photos, files etc)

Pete.
 
Hi there,

I have Hweld SMAW inverter welding machine .... machine power on but no arc in it kindly help me if ay one knows about this...
this is chinese machine and there is no picture on any type of manual on internet
 
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