Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting Game Consoles & Other Weird Devices
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 12-11-2020, 04:42 AM   #1
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,077
Question Inverter welder help

Good day folks. It's been a while since I've actually repaired anything, so today I have something I haven't worked on before: a friend of mine gave me this small inverter welder to look at. It powers on, but doesn't work.

I took the cover off and immediately noticed the problem: two dead G40N60 transistors, along with some SMD resistors in what I think is the gate drive for the trannies. One IGBT is dead-short, the other reads fine, but it's missing a chunk of the casing, plus its SS14 diode is also gone, so it's safe to say we'll be replacing both.

The SMD resistors are by far the biggest issue, since I'm not able to make out what value two of them are. I can see 5R1 on one pair, but the other is completely gone. All I can see is a 1 and a 0, but nothing in between....if I had to hazard a guess, I'd say it's 150, but that could be totally random....

The welder is an ESAB MMA 300 if it matters at all. Without a schematic, I was hoping someone may recognize the circuit and offer some approximation to those values, since it looks "generic" enough and I recall seeing this shape and size under other brand names too on the shelves...it may not even be worth repairing it, given how expensive those transistors can get, especially since there's the risk of blowing them again. It's almost identical to THIS one, except it's got an ammeter at the front. The blurry schematic does actually show those 5R1 resistors in the gate drive on the far right of the page there, but the schematic is not clear enough to work out what IGBTs it uses, so I'm not sure if those values would work in mine as well. Of course, I'm grasping at straws, but this would mean the blown resistors are 20R ones, which comes close to the 150 value I'm betting on...
Attached Images
File Type: jpg 20201211_121502.jpg (586.1 KB, 17 views)
File Type: jpg 20201211_121521.jpg (495.7 KB, 11 views)
File Type: jpg 20201211_114533.jpg (435.6 KB, 15 views)
__________________
Wattevah...
Dannyx is offline   Reply With Quote
Old 12-11-2020, 09:57 AM   #2
stj
Great Sage 齊天大聖
 
stj's Avatar
 
Join Date: Dec 2009
City & State: Europe
My Country: some shithole run by Israeli agents
I'm a: Professional Tech
Posts: 24,386
Default Re: Inverter welder help

so it's just a stick welder, not even a mig?
those things are sooo cheap now that it's not worth the time.
stj is offline   Reply With Quote
Old 12-11-2020, 10:23 AM   #3
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,077
Default Re: Inverter welder help

Quote:
Originally Posted by stj View Post
so it's just a stick welder, not even a mig?
those things are sooo cheap now that it's not worth the time.
Yes, it's a stick welder - tiny too. It's like a small UPS

I'd hazard a guess it's the dust buildup that killed it: there was a LOT of dirt caked on the legs of the two transistors. It's not the fluffy dust you get on the inside of electronics or PCs - it was more like dust that got moist and turned into mud which then dried off....that kind...

Last edited by Dannyx; 12-11-2020 at 10:31 AM..
Dannyx is offline   Reply With Quote
Old 12-11-2020, 04:19 PM   #4
stj
Great Sage 齊天大聖
 
stj's Avatar
 
Join Date: Dec 2009
City & State: Europe
My Country: some shithole run by Israeli agents
I'm a: Professional Tech
Posts: 24,386
Default Re: Inverter welder help

the crap may even be conductive,
remember before welding you clean the surfaces with a grinder!!
metal dust!!!!
stj is offline   Reply With Quote
Old 12-11-2020, 04:23 PM   #5
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,077
Talking Re: Inverter welder help

Quote:
Originally Posted by stj View Post
metal dust!!!!
+ fan on the back to help suck it in
Dannyx is offline   Reply With Quote
Old 12-11-2020, 05:42 PM   #6
petehall347
Badcaps Veteran
 
Join Date: Jan 2015
City & State: worcester
My Country: United Kingdom
I'm a: Knowledge Seeker
Posts: 2,679
Default Re: Inverter welder help

needs an air filter then
petehall347 is offline   Reply With Quote
Old 12-11-2020, 08:01 PM   #7
stj
Great Sage 齊天大聖
 
stj's Avatar
 
Join Date: Dec 2009
City & State: Europe
My Country: some shithole run by Israeli agents
I'm a: Professional Tech
Posts: 24,386
Default Re: Inverter welder help

needed an air filter - not any more!
stj is offline   Reply With Quote
Old 12-11-2020, 08:17 PM   #8
CapLeaker
Leaking Member
 
CapLeaker's Avatar
 
Join Date: Dec 2014
City & State: Atlantic Canada
My Country: Canada
Line Voltage: Ground, 0Hz
I'm a: Hobbyist Tech
Posts: 4,666
Default Re: Inverter welder help

my take on it is a 750, as being 75 Ohm.
CapLeaker is offline   Reply With Quote
Old 12-12-2020, 09:14 AM   #9
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,077
Default Re: Inverter welder help

Could be...what's the worst that can happen

Now that I look at it more carefully, it could be a 7 after all, the way the line seems to curve ever so slightly...
Dannyx is offline   Reply With Quote
Old 12-12-2020, 09:54 AM   #10
petehall347
Badcaps Veteran
 
Join Date: Jan 2015
City & State: worcester
My Country: United Kingdom
I'm a: Knowledge Seeker
Posts: 2,679
Default Re: Inverter welder help

be better buying a new welder and adding a filter
then maybe looking at values of unknown resistors .

Last edited by petehall347; 12-12-2020 at 09:55 AM..
petehall347 is offline   Reply With Quote
Old 12-12-2020, 04:51 PM   #11
CapLeaker
Leaking Member
 
CapLeaker's Avatar
 
Join Date: Dec 2014
City & State: Atlantic Canada
My Country: Canada
Line Voltage: Ground, 0Hz
I'm a: Hobbyist Tech
Posts: 4,666
Default Re: Inverter welder help

Quote:
Originally Posted by Dannyx View Post
Could be...what's the worst that can happen

Now that I look at it more carefully, it could be a 7 after all, the way the line seems to curve ever so slightly...
Nothing. The gate drive resistor just limits the current. Common to see up to 100 Ohm resistor there.
CapLeaker is offline   Reply With Quote
Old 12-12-2020, 04:54 PM   #12
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,077
Default Re: Inverter welder help

Quote:
Originally Posted by CapLeaker View Post
Nothing. The gate drive resistor just limits the current. Common to see up to 100 Ohm resistor there.
So I guess if it's too high, the gate would be insufficiently driven and the transistor would overheat (linear region ???).

If it's too low = too MUCH base current...
Dannyx is offline   Reply With Quote
Old 12-12-2020, 08:19 PM   #13
CapLeaker
Leaking Member
 
CapLeaker's Avatar
 
Join Date: Dec 2014
City & State: Atlantic Canada
My Country: Canada
Line Voltage: Ground, 0Hz
I'm a: Hobbyist Tech
Posts: 4,666
Default Re: Inverter welder help

Yeah, the gate resistor has to be selected. All depends on the IGBT, switching time, etc...
However, yours look like 750 to me, which is 75 Ohms.

Last edited by CapLeaker; 12-12-2020 at 08:21 PM..
CapLeaker is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2021
Powered by vBulletin ®
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 05:54 AM.
Did you find this forum helpful?