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  1. #1
    Join Date
    Jun 2010
    Location
    Seguin, Tx
    Posts
    153

    Hobart beta mig 170 repairs

    https://youtu.be/w6KJOr8tqAM
    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. When pulling the trigger on the gun, that feeds + voltage to J4-1 and - voltage J4- 2. I have voltage present when pulling the trigger on the gun. If I cannot repair this board can someone 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 only see two diodes 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 wirefeed motor voltage. 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. 82D4A4FE-D6D0-4BC1-9CCD-69E05DA7222C.jpg
    Last edited by jeff-; 10-09-2017 at 10:09 AM.
    Jeff's CNC Plasma Cutting

  2. #2
    Join Date
    Sep 2003
    Location
    Clark County, NV
    Posts
    5,258
    Quote Originally Posted by jeff- View Post
    ...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 sense to me...
    Diagnostics on this machine are most certainly not my area, but I do note that 27.4 * 2 = 54.8.

    Could it be that your "27 VAC" and your "55 VAC" are just line-to-ground and line-to-line, respectively, and normal for transformed control voltages?
    Last edited by MAC702; 10-09-2017 at 12:05 PM.

  3. #3
    Join Date
    Jun 2010
    Location
    Seguin, Tx
    Posts
    153
    Yes that is my thinking as well. I’m going to replace U1 and a couple of other components and try it again.
    Last edited by jeff-; Yesterday at 09:36 AM.
    Jeff's CNC Plasma Cutting

  4. #4
    Join Date
    Jun 2010
    Location
    Seguin, Tx
    Posts
    153
    Made some progress repairing the control board. Replaced the ICís TL494CN location U1, LM324N location U2, LM317T location U3, TIP122 location Q6, 2N6668 location U8, 2N6292 location U9. Also made some modifications to the board. In case any of these ICís go bad again I will not have to unsolder and resolder components as I soldered in plugs for U1, U2 and U8. U8 also soldered in a leaded plug and installed another heat sink as I suspected It could have been overheating a bit. I might even install a little 24volt fan to blow on the board to keep it cool. Well hope this will help others with the same problems.

    A1E28C65-8BBD-4888-BAC3-54F69CC07C6F.jpg6C5AD312-E812-4C2E-B010-02356956867C.jpg30B2647C-2EBE-487C-B005-BB0D24110521.jpg
    Last edited by jeff-; Yesterday at 09:45 AM.
    Jeff's CNC Plasma Cutting

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