Damaged PCB

[Big Jake]

I'm not sure if this is the right thread for this, but here we go. I just bought a Miller Maxstar 200 STR at an auction for very cheap because it had a scrap tag on it. Being the kind of guy I am, I figured the risk was worth possibly ending up with a 40lb paper weight. Someone had already dug into this unit and did some work on it and gave up, so there are signs of someone messing with it and one component missing.

I am wondering if anybody would be able to help me identify what the missing components are. I called Miller's customer service and they were very understanding, but couldn't find a bill of materials for the particular board, the power interconnect board. The number on the board says 200851. I only have 3 components that I can't identify that I have below. The rest of the damaged components are easy enough. The ones that are missing are labeled Q1, Q11 and what I am thinking is R6.




I have looked over all the boards thoroughly and the damamge was minimal. I know that damage on this board can let all the magic smoke out on all 3, but I might be lucky on this one. I realize that I might get it all back together, flip the switch and destroy all 3 boards, but that doesn't bother me too much. I could at least say I tried.

[ronsii]

Wow!!! that's some serious carnage there

Looks like someone hit the board with some very high voltage!!! especially to blow the ends off the resistors like that....

Q1,Q11 are probably a matched pair of npn/pnp fet's probably a lot that would work but be best to find an exact replacement... someone around here is bound to have a similar welder... or maybe user ccawgc will chime in

I'd make a list of the whole board... ie make you own BOL - spreadsheet all the R's, D''s Q's.etc... then you probably find that R6 is actually D6 ... plus with the list you'll know what component you just blew when you try to power it up later on

[ccawgc]

The damage that points to the pins RC2. Burnt circuit traces has me worried.
The boost pcb may have taken a dump and the IPM may be bad also.
Seen to many of these that won't turn on and all three are bad.
All the parts that failed were caused by some thing else. so keep looking.
your biggest problem might be that the pcb is multilayered. so there could be hidden
unrepairable damage.
don't have a maxstar open right now.

[Big Jake]

Thanks fellas.

Ronsii, I like the idea of the full list. I just did one in my head to figure out the designator for the one that is burned up and R6 is the only one I can't find otherwise.

Ccawgc, I have been checking as much as I can, but like you said, a hidden trace could easily be missed. The other boards really don't show any signs of being bad, but who knows with those. I think at this time, it is a flip of the coin on whether or not I keep pursuing it or run away. If I run away, it might be a while before I get a welder that I can start practicing TIG on.

[cwby]

Check with Innovat corporation. They repair boards & might be able to help.
https://innovatcorp.com/pc_board_repair_price_list

[fuzzy7k]

Did you ever find out the value of R6? I have a similar situation. On mine, I have a bad input diode that I think caused the problem. My main caps are also on the line for being out of spec. One is one isn't. I've identified all of the parts that I would like to replace but verifying this resistor is holding me up from ordering parts. I found a few images with R6 shown, but I can't come to a conclusion on the result.

R4 is also naked on mine, meaning it's colors & case have been burnt off.
Looking at pictures I see different stuff
(Br ? Bk Bk Br/Gd) - 1?0 x1 1%/5%
(Br Bk Bk Gd Br) - 100 x.1 1% = 10ohm 1%
(Br Bk Bk O Br) - 100 x1k 1% = 100kohm 1%

If I check it with a meter I get a reading of 127.27ohm, so I'm assuming it should be (Br O Bk Bk Gd), but it's also toast, so ?

Unfortunately our boards are not the same, mine is 207818. Maybe R6 is different, maybe not. Hopefully someone else can chime in.

[whtbaron]

The OP hasn't been here since 2021... someone else might chime in with some expertise...

[Big Jake]

I never did find out what the value of that resistor was. As it turned out, the more I looked at the board, the more damage I found, so it was a lost cause. I ended up buying a Primeweld tig welder instead because the price of all the replacement boards was going to be more.

[Weld_]

Did you ever find out the value of R6? I have a similar situation. On mine, I have a bad input diode that I think caused the problem. My main caps are also on the line for being out of spec. One is one isn't. I've identified all of the parts that I would like to replace but verifying this resistor is holding me up from ordering parts. I found a few images with R6 shown, but I can't come to a conclusion on the result.

R4 is also naked on mine, meaning it's colors & case have been burnt off.
Looking at pictures I see different stuff
(Br ? Bk Bk Br/Gd) - 1?0 x1 1%/5%
(Br Bk Bk Gd Br) - 100 x.1 1% = 10ohm 1%
(Br Bk Bk O Br) - 100 x1k 1% = 100kohm 1%

If I check it with a meter I get a reading of 127.27ohm, so I'm assuming it should be (Br O Bk Bk Gd), but it's also toast, so ?

Unfortunately our boards are not the same, mine is 207818. Maybe R6 is different, maybe not. Hopefully someone else can chime in.

If your checking resistors you need to pull them from the board otherwise you're not going to get the correct reading.

[danielplace]

If your checking resistors you need to pull them from the board otherwise you're not going to get the correct reading.

One side at least. Lol.

[smithdoor]

I hope has fixed by know.
It more fin to read 📖 than to chime in

Dave

The OP hasn't been here since 2021... someone else might chime in with some expertise...