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Trailblazer 301G, tech issues. Help

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  • Trailblazer 301G, tech issues. Help

    hey guys, trail blazer 301G, runs great, got this thing in a trade.. makes 110 and 220v, but nothing to the leads. Im hearing pc board issues? Ive checked the fuses on the boards, they are good. Previous owner said they jump started it, then this happened. Soo, im a diesel mechanic, and im very inclined to fix this myself, but i dont know where to look, or what to test. So, does anyone know what board it could be? Or which components could have gone bad on the board?
    maybe its something else, im itchin to get to the bottom of it, thanks!

  • #2
    Please post your serial number so we can look at the correct manual.
    I have an old Trailblazer 280NT; when I bought it, it was old but had less than 200 hrs on it. Asked here about anything to look out for, and was strongly warned NOT to ever jump start it or I would most likely lose a PC board. Sounds the the previous owner never got that warning.

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    • #3
      Thank you for the reply! The serial is LC361532

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      • #4
        Are you experienced/comfortable poking around in hot circuits? Dont get yourself killed trying to fix this.

        Here is the manual if you don't have one
        https://www.millerwelds.com/files/ow...O4407M_MIL.pdf

        My off-the-wall guess is you have a bad PC1 Power PCB. Need to see if you have any power at the "main field" brush, and it should vary when you change the current setting. That board is likely around $500 if you can find one. Miller4less doesn't list it, but BR welding shows a substitute part number. Worth a call to Miller tech support for help.

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        • #5
          Originally posted by Aeronca41 View Post
          Asked here about anything to look out for, and was strongly warned NOT to ever jump start it or I would most likely lose a PC board.
          I have also heard this advice and I do not question it's validity but I wonder if you might have some insight to the reason it should happen? Assuming the connections to boost were made correctly why/how does that cause the PCB to get toasted?

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          • #6
            Ive been shocked a time or 2, i will start testing. Im assumming when these boards go out, its just one or two components of the board, right? My intention is to find out exactly which components and solder in new parts. Could be a whole lot cheaper if i could do that

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            • #7
              Originally posted by Onsite View Post
              Ive been shocked a time or 2, i will start testing. Im assumming when these boards go out, its just one or two components of the board, right? My intention is to find out exactly which components and solder in new parts. Could be a whole lot cheaper if i could do that
              It sure would. Lest we be led down a wrong, potentially expensive, path, you want to do a lot of testing before replacing the board, but you already know that. And if you have the skills and equipment to repair it, so much the better. That would be my approach. Check that the brushes slide very freely in their holders, and look for poor connections everywhere.

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              • #8
                Originally posted by Meltedmetal View Post
                I have also heard this advice and I do not question it's validity but I wonder if you might have some insight to the reason it should happen? Assuming the connections to boost were made correctly why/how does that cause the PCB to get toasted?
                I'm with you. Doesn't really sound logical to me but facts are facts and there is a lot of history that says don't do it. Not dumb enough to press my luck! I am a retired systems engineer with about 50 years of electronics-focused background, and spent a lot of time "fixing" multimillion dollar gadgets along the way. I always want to know why, but have not had time to dig into this one. Guys have said that it will happen even if you do everything right--no reversed connections, etc.

                I thought retirement would allow a lot of spare time to run down interesting rabbit trails like this but that is just not the case. Maybe someday. For now, I just won't jump it. And, since Miller doesn't release board schematics, you're at a real disadvantage trying to figure it out.

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                • #9
                  I don't know how other people boost things but I've had a face full of battery acid in the past from such an endeavor and I have to say it wasn't really all that much fun. Consequently when I attach booster cables the last connection I make is the ground on the to be boosted vehicle and I attach to the engine block so that if it sparks I won't repeat my past experience.
                  I wonder if in boosting these welders that 2 ground circuits, one at high potential and one at lower potential could be the culprit resulting in some strange current draw though the circuit board. Just a thought.

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                  • #10
                    Sounds like a really ugly experience! I too ground somewhere besides the battery. A friend had a similar experience. My 2002 GMC truck had a bracket sticking up over the No1 cylinder marked "Ground". Nice feature. I don't think its there in my newer one.

                    As to the TB ground circuits, I have no idea. I suppose its possible. I would assume that most people connect both leads to the battery, so it wouln't seem to be part of the problem, but maybe they don't and that's the reason.

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                    • #11
                      That was my next question, where to get a board schematic? I see you say they are not available huh?
                      So, what would be yur best start point? Just start testing literally every single resister and capaciter, etc?

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                      • #12
                        You can find the inputs and outputs from the schematic in the owners manual. First I'd look for anything obviously burned or cracked then try to see if I could figure out the circuit design to some degree. We know it has to take input from the current adjust pot and vary the current in the exciter winding. So, there must be a couple of amplifiers and probably a regulator of some sort. You will need someone with circuit card experience. Unless you are really good at board repair it is not likely all the components will survive being taken off for testing and put back; you will need some paper work first to find the aspect parts. Could start by seeing if the current adjust pot changes the voltage input to the board and then try to trace it through the board. As I said, requires a person with some circuit design knowledge. Another off-the-wall chance is keep scanning ebay for a Tech Manual for the welder. They do show up every now and then, and have schematics.
                        Last edited by Aeronca41; 12-13-2017, 11:20 PM.

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                        • #13
                          Originally posted by Aeronca41 View Post
                          Sounds like a really ugly experience!
                          While it wasn't fun I don't think I came out more ugly after the experience than I was before. I got lucky as it were, it mostly missed my eyes and it was winter so there was lots of snow around. I did a quick face plant in a snow bank and lots of scrubbing snow on my face and neck. No permanent damage to me but my clothes caught it bad. Every place the acid hit them it left a hole eventually. The "good ole days."






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                          • #14
                            Yeah--some of the good ole days were better than others.....sometimes amazing we survived them all in the exuberance (and sometimes stupidity) of youth. I was blessed to grow up welding around a lot of heavy equipment with my dad, who was very attentive to risky situations after losing most of the fingers on his right hand during WWII. I don't think we ever had a major accident, but we sure used a lot of cribbing and chains, and did a lot of thinking before acting.

                            Onsite, we're hijacking your thread a bit, but what are you thinking? Have you looked at the board yet? Are you familiar with how to deal with protecting the components from static electricity while you're working with it? Dont want to cause any new problems while trying to find the existing ones. It is likely that the current control is fed a reference voltage from the board, which it in turn varies and feeds back to the board. Ultimately, it has to be varying the voltage at the exciter brush after flowing through the various board functions.

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