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Big Blue 300 Pro problems

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  • Big Blue 300 Pro problems

    I have a guy that brought in a Big Blue 300 Pro with the Cat diesel about 6 months ago that was throwing out a HELP 20 code. Come to find out it had a bad control module. Changed it out. When I first fired it up, it went up to half voltage, 20 volts, and hung there for about 10 seconds and then went to the full 41 volts. I let it run for awhile, load banked it and test welded with it and everything checked out. He came and picked it up the next day and he tested it before he left the shop. When we fired it up for him to weld with it, it hung at half voltage for about 10 seconds and then went to full voltage. He welded with it, said everything was fine and took off with his machine to do a job in Utah.
    He called me about a week later and asked me about the 10 second pause at half voltage. I had never seen that before so I told him to bring it to me after he got back home and we would check it out. A month after that, he called and told me that the 10 second pause had slowly turned into a 2 minute pause and that he was only getting half of the AC output at the receptacles too. Not much I could do over the phone so I just told him to bring it back when he got home.
    He got home last week and brought me the machine the day after. What was a 10 second pause when it left had turned into an hour +. I have ran every test that I could find on it. I even took up half of Lee in the tech department's afternoon trying to chase this bug down. I jumpered around the control module like Lee said and got the AC to full voltage at the receptacles so that ruled out the regulator board. I did my checks on the control board and the only problem I could find was that wire 107a didn't have 10 volts coming out. I couldn't find a diagram for the board so I have no idea what the board has to see coming into it before it will throw the 10 volts out to the regulator on wire 107a. Has anybody seen this problem before that could share their experience with me? Cruizer?

  • #2
    In the 2 regulator boards I've checked from the same machine, both lems are shot. Making me think that the revolving field current is too high


    • #3
      Ok. I will give that a check.


      • #4
        Help 20

        I have a help 20 issue as well on my Miller Big Blue 300. I have a few questions.

        I checked my voltage across the welder outputs, receptors and got none.

        I was wondering what it would cost to take it in, what parts and repairs i should be looking specifically for them to replace. Is there a specific instrument tester that they use to diagnose the circuitry.


        • #5
          It's quite a technical machine ,best take it to Miller service center. There is really nothing in there that can be tested by an untrained ( in welder repair) person