ESAB Migmaster 251 problem

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Hello, new here and I need some help. I got what looked like a very good deal on an ESAB Migmaster 251. Was told motor was bad on wire feed. Well got it for couple hundred bucks and figured well i can repair this. Plus I had a old l tec -35 feeder that I reworked and got working great after fixing some bad SCRs on the governor board. So if the feed didnt work I was gonna use my l-tec 35 and use the 251 as a power supply. Ok first fixed the wires on the gun and got no power out nor the wire feed motor would not work. I opened up the cabinet and found a control board with a visible charred resistor, I think R78?, much like a thread I found in the forum. The board is a 38111. No longer available from ESAB. The previous thread eluded to a bad scr causing the resistor to fry. And it looks like its the main voltage control scr in the rectifying bridge is what was bad. Where the previous thread drops off was that I dont know the value of the resistor, and if other components were bad too on the board. If he was able to repair the board himself or sent it out. I am planning on checking the large power SCR's for functionalty using standard tests. Just need to get some more gaps in the story filled in so I can repair my welder.Tom
Reply:A quick update, checked the main SCR's by turning on the unit with no board installed and the voltage at the -/+ terminals is 120 volts all AC!! Looks like the main SCr's are shot. I suppose this dumped high voltage back to the board thru the gate terminal, i can heck that with meter and fried the resistor. Need a couple new SCR's and board repaired. Anybody do the board repair themselves?
Reply:Ok the story gets a little more clearer now. After the above up date I removed the SCR's on large rectifiying bridge, 180 amp capacity, and bench tested with a mukltimeter. With anode on the red lead and the cathode on the black led reads an open circuit. Swapping the leads, red to cathode and black to the anode again reads an open. If I retrun the red to the anode and black lead to the cathode and just touch the red gate wire of the SCR to the anode the SCR conducts. Both SCR's are good. I dont know why the board is bad but I sent it out to Innovat Corp in west virginia for reworking. Hopefully after reworking the board will be okay but I dont know why r78 was overheated. Any inputs out there?
Reply:Following with interest.  I was just given a 251 with a 2E feeder and a spool gun by a friend.  Deal was pay what I think it's worth if I can get it running.  If not it's headed to the scrapper.  Mine powers up and spool gun appears to feed fine, haven't tried to see if it has welding output yet.  My unit does not have an integrated wire feed.  When I plug in the feeder triggering the gun triggers the gas solenoid on the feeder but nothing else and the power light on the feeder is off.   Is this similar to what was going on with yours?  I am just a hobbyist, and frankly don't even know what an SCR is, lol.
Reply:Hello,   I didnt hook up the gas to the unit. Was planning on running flux core wire. So I dont have the schematic close at hand but I remember the power light has a couple fuses/circuit breakers that it runs thru. On my unit these breakers are under the wire spool storage compartment. I would check that first on the power light issue, light bulb could be burned out too. Does the unit hum when ya turn it on?
Reply:Also, if you open the main electrical side of the cabinet there is a circuit board in there with 3 connectors on it. its about 8 inches by 6 inches and the only one there. See if any components looked over heated. Mine had a resistor over heated and it was on the upper left hand corner of the board. Resistor R78 I think.
Reply:Hydrogeo, I googled esab migmaster 251 and found the manual which has the electrical schematics. Page 24 is of keen interest, shows all electrical connections. Bottom right corner is a good place to start as I did, there are heavy copper jumpers that configure the machine for the proper voltage you are plugging it into. Mine is 208 and when i checked they had it not even set right. On the machine under the wire spool compartment there is a panel about a foot wide. Remove this with power off of course, towards the front you will see a small 5 inch by 5 inch size heavy insulated board with jumper information embossed on it make sure these are set right. per the instructions on this board and the schematic. Where are you located btw?  Here is the manual link: https://www.esabna.com/literature/ar...f-15-357-a.pdf
Reply:Hydrogeo, I googled esab migmaster 251 and found the manual which has the electrical schematics. Page 24 is of keen interest, shows all electrical connections. Bottom right corner is a good place to start as I did, there are heavy copper jumpers that configure the machine for the proper voltage you are plugging it into. Mine is 208 and when i checked they had it not even set right. On the machine under the wire spool compartment there is a panel about a foot wide. Remove this with power off of course, towards the front you will see a small 5 inch by 5 inch size heavy insulated board with jumper information embossed on it make sure these are set right. per the instructions on this board and the schematic. Where are you located btw?  Here is the manual link: https://www.esabna.com/literature/ar...f-15-357-a.pdf
Reply:Originally Posted by tkupiecHydrogeo, I googled esab migmaster 251 and found the manual which has the electrical schematics. Page 24 is of keen interest, shows all electrical connections. Bottom right corner is a good place to start as I did, there are heavy copper jumpers that configure the machine for the proper voltage you are plugging it into. Mine is 208 and when i checked they had it not even set right. On the machine under the wire spool compartment there is a panel about a foot wide. Remove this with power off of course, towards the front you will see a small 5 inch by 5 inch size heavy insulated board with jumper information embossed on it make sure these are set right. per the instructions on this board and the schematic. Where are you located btw?  Here is the manual link: https://www.esabna.com/literature/ar...f-15-357-a.pdf
Reply:Made a bit more headway with mine.  I found that the mig torch has welding current, but I checked with a multimeter and no power is making it to the feed motor. Also found that the spool gun also has welding current and the feed on that does work. I just haven't verified the solenoid operation, but it appears that I'm good to go with that.   I opened the case on the 2E feeder and nothing is obvious, so I am going to crack open the case on the 251 to see if there is anything obvious in there.  the wiring diagram in the pdf manual for the 2E isn't the easiest for a novice to follow, but I'm going to give it a shot.
Reply:If ya post the spool gun schematic here I can help you along.
Reply:If you find the positive motor connection and negative connection you can use a battery charger or 12 volt car battery and see if the motor itself works, of course isolate the spool gun electrically from the unit so just the 12 volt source is connected and not the internal circuitry of the welder.
Reply:Originally Posted by tkupiecIf you find the positive motor connection and negative connection you can use a battery charger or 12 volt car battery and see if the motor itself works, of course isolate the spool gun electrically from the unit so just the 12 volt source is connected and not the internal circuitry of the welder.
Reply:Okay just what i needed, M1, bottom left side of first schematic, is the motor for the wire feed. Its a variable voltage dc motor, low voltage say 12 vdc motor turns slow, higher, voltage say 70 volts speed goes way up.  So if you are applying the dc voltage correctly +12 to the red lead ground to the black then it should spin, try tapping the motor while doing this. could be brushes are worn out too, anyway to get tot he brushes to see how they look?
Reply:From the bridge its looks like 42 volts is max for the spool gun motor.
Reply:When ya try the battery or battery charger make sure ya complete the circuit by applying both the negative lead and the positive to correct connections to the wire feed motor.
Reply:Okay,   I have some updated info here. Innovat has repaired my 38111 board. It is being shipped now back to me. I asked what causes this failure and Innovat technician has informed me that this is a very common problem and that a bad main SCR fails and backfeeds hgh voltage thru its gate connection and fries the board. The lm324 op amp burns out along with the R78 resistor. Perhaps a in line fuse would be best added here to prevent future events? But anyways I went back abd double checked both SCR's and one is not working correctly. I had bought two new ones already so I have replaced both of the SCR's now and just waiting on the board at this point. Will update when i get the board.
Reply:Where did you get the SCR's from?Tom
Reply:I found 2 2N3888 scr's on ebay for 25 bucks a piece, 175 amp 1200 volt rated stud mounted. Installed them and they worked fine. The welder is now fully functional and the resistor R78 is a 100 ohm 5 watt resistor. One IC was replaced and along with the resistor and it works now, wire feed motor and the welding current all is good!!!
Reply:Good deal, glad to here your back up and running.How much did they charge to repair the board?Tom
Reply:The repair cost 180 bucks plus shipping, they did it in like a week or so including shipping time from virginia to new york.
Reply:So a quick update on my 251.  I popped the cover and tried to chase the problem down. It appeared to point to the board but I ran out of patience.  I figured for what I have into the machine it was worth having the local ESAB dealer take a look.  They confirmed it was a bad board.  They gave me the option of either sending out the old board for a rebuild or getting a new board from ESAB (which they said are available).  There was a fairly hefty price difference, and I'm just a hobbyist so I'm going with the rebuild.  They did say it is a solid machine that was worth fixing.
Reply:Originally Posted by tkupiecI found 2 2N3888 scr's on ebay for 25 bucks a piece, 175 amp 1200 volt rated stud mounted. Installed them and they worked fine. The welder is now fully functional and the resistor R78 is a 100 ohm 5 watt resistor. One IC was replaced and along with the resistor and it works now, wire feed motor and the welding current all is good!!!
Reply:Originally Posted by tkupiecI found 2 2N3888 scr's on ebay for 25 bucks a piece, 175 amp 1200 volt rated stud mounted. Installed them and they worked fine. The welder is now fully functional and the resistor R78 is a 100 ohm 5 watt resistor. One IC was replaced and along with the resistor and it works now, wire feed motor and the welding current all is good!!!
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