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Hobart beta mig welder, wire feed control repair

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Jeff Nading

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Hello all,
Was hoping to get some help repairing the control board off of my Hobart beta mig welder, here is the schematic of the board. I have replaced the Q8 and Q9. Q8 being the wire feed darlington power amp, TO 220 case, and is a PNP D45E3. The schematic shows this to be an NPN D44E2, the BOM from the manufacture show this to be a PNP, I also checked with the factory tech he stated there was a misprint on the schematic and gave me the correct component number for the Q8 location. Repaired/replaced the copper braiding end crimp connectors on the wire feed cable assembly as this copper braided wire serves to feed high amperage from one end of the wirefeed cable assembly to the other end (tip end). Was having issues with the wire locking up in the cable core because of the core flowing amperage instead of the copper braiding, this would cause the core to heat expand and lock up the wire, so the cable feed is good now. I was not able to weld 1” before I repaired the cable feed, now I can weld about 6”, then the wire feed motor starts to shutter, slow and stop. I can the release the gun trigger, pull the trigger again and start again, same thing happens. The wire feed motor pulls 4 amps @ 18.3 volts DC under load @ max speed, with no load the motor runs fine, the motor is rated for 24 volts DC, the D45E3 is rated for 10 amps, this should be good enough. I’m thinking something is going wrong with U1, TL494CN, could this be possible? This board is NLA. Can you also tell me if I am correct in thinking when pulling the trigger on the gun, that feeds + voltage to J4-1 and - voltage J4- 2, I have not traced out these wires yet, but don’t have voltage present when pulling the trigger on the gun. If this board cannot be repaired can you recommend a speed control board that I could use in conjunction with this board, just to control the wire feed alone? I checked incoming voltages to the board, most pins on J1, 1 through 12 and have 27 volts AC, one has 55 volts AC. This does not make since to me, I see nothing on the board to rectify the voltage to DC or am I missing something? The 6 pins on J2 are the potentiometers, 1 through 3 for voltage control and 4 through 6 for the wire feed. J5 and J6 are the motor voltage. Well I have searched the internet and cannot find a wire feed control board to marry to the board I have. Hope you guys can help. Thanks, Jeff.
 

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Jeff Nading

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Repairing the braided copper wire that feeds amperage from one end of the cable to the other end, gun end and feed tip. Used copper fittings and copper tubing for the crimps.
Date now is 11-4-17, two months after making this video I finally got the welder running perfectly. On the cable repair I ended up making a copper bushing 3/4” outside diameter inside was close to 1/2” diameter, thicker than what the plumbing fitting was. The steel block tool I made worked wonderfully to crimp the bushing. I replaced the darlington PNP amp on the board and other components, the board was good again. Still had a slight problem , wire feed control would all of a sudden stop. Started checking other wires, found a thermal disk breaking down in the wire feed circuit, when welding it would open at low temperatures, replaced it and now my welder works very well. My determination was the instrument of success in repairing my Hobart welding machine.
 
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