HELP......electronics guru needed !

lol.... I had a pc board go bad in one of my tig welders. I do have the schematic of it. Trying to find the resisters and transistors... but what I find looks different than what is on the pc board. Can anyone help me ? I can post pics etc when needed.

 

Post up pics. I'm a hack at this stuff, but I've fixed things like this in the past.

 

Discoloration. From going "WHOOF."

 

The resistor and transistor are pictured here.....
The resistor list as "resistor,c 1w 10 ohm +/-5
Not sure what type of resistor it is, and ones I have found have been tiny compared to this one.
The dimentions of the body are :
Dia. .225"
Length .565"
Leg dia. .040"

Transistor lists as 9a 50V.

 

My electronics prof theorized that electronics were smoke powered. Once the smoke got out, things stopped working.

 

I believe this also.....

 

Yep, you let the smoke out and it doesn't work anymore.

 

Bad lighting, but those caps and transformer also look suspect. Have you checked eBay for a replacement board?

 

Board is dirty... in the second picture there is some smoke damage...
have checked eBay.... no luck.

 

That resistor is likely where the problem originated, and may be the onoy component that is actually toast. Its probably a 250v resistor, which is why its bigger.

 

What's the make/model of the TIG?

 

It looks like the resistors are all labeled R, the diodes are Q, the rectifiers are D. Check your rectifiers by seeing if you have continuety one way but not the other. You can look up the resisters and check their ohms. I’m not sure how to test a diode. You need a special meter to check capacitors Which are labeled C. I would try to trouble shoot the board but I wouldn’t expect to fix it.

 

Miller synchrowave 250

 

Diodes are one way gates-- continuity flows one way but not the other. You may need to renove the components and bench test them to get accurate tests.

 

The labeling on the board matches up to the parts list. The blown resistor is "r77" which is listed below.....

 

I'll check to see if I can find a spare board for cheap, might save you some grief.
May need the ser. #, I'll PM if so.

 

Looks like this is your board, the next page starts with the test point voltages.

Control Board Pc1 Testing Information (use With Section 6-5) - Miller Electric SYNCROWAVE 250 Technical Manual [Page 34]

 

Looks like there's a lot of Miller PCB failures out there. That's troubling, especially since they are a Wisconsin company. I'll look for the PCB part number, but it looks like you can get a replacement PCB pretty readily.

It looks like a few components are suspect on that board.

 

I'd replace the board. When you have several cascaded failures, like it looks you did, you are unlikely to fix it by replacing the obviously bad parts. One blown capacitor or burnt resistor, sure. But probably not that board.

 

The burned resistor is due to something else shorting putting too much current thru it. Burned ressitors like that are seldom the cause of a problem. Used to work in two way radio and tv and radio broadcast and saw many burned resistors due to another part failure. It looks to be a very standard type of resistor. Doesn't look like it is a wire wound one.