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Miller blue star 180k

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  • Miller blue star 180k

    Well she been running great for over a year after the last issue until I need to run some beads on my mower deck today. Fired her up and got ready to strike an arc and nothing. After trouble shooting with multimeter I found out she wasn’t generating power. Pulled top cover to get to F1 fuse and sure enough it was open. Replaced and am generating partial power, getting 90 volts AC out the receptacles and 50 volts out the weld leads DC. Checked hertz out the receptacles was at 60 which it has always been around there. Only thing I’ve changed on it was a couple weeks ago I replaced a leaking oil pressure switch. Could that have anything to do with this? Also wandering if whatever that F1 fuse protects got damaged before it blew. And worth mentioning I replaced the F1 fuse with a 15 amp 250 volt fuse from the hardware store that is for a microwave. Any input much appreciated.

  • #2
    Just checking it out again and discovered F1 fuse is blown again.

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    • #3
      Check out diode bridge SR1 with an ohmmeter. May have a bad diode. First place I'd look.

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      • #4
        Is SR1 on the PC1 board?

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        • #5
          I’m no electronics expert nor does my MM have a diode test function but visual shows to have a hot spot in the top corner of SR1. What say y’all?

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          • #6
            Need your serial number.
            That burn spot is certainly suspicious, but I'm not sure that's the SR1 I'm talking about. Have to look at the correct manual. That is obviously PC1SR1, but there is another SR1 that is not part of the PC board. I suspect there is no diagram for the board in the manual, so it may not be possible to isolate the problem that way. However, it could be your problem, and it's not hard to check. Let's find the correct manual first.

            Good news. You don't need a diode test function on your meter to check diodes. A plain old ohmmeter will work just fine--we were finding bad diodes with vacuum tube voltmeters and Simpson 260s for at least 40-50 years before diode test functions were invented. You will have to take that bridge off of the board to check it; if you are not experienced in soldering PC boards, be very careful--you can permanently damage the board and the part with bad technique.

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            • #7
              Will get a serial number posted when I get back to the house. Definitely not gonna remove anything from that board since I have no experience soldering back to pc boards. I did check some of the other diodes on the board with the ohm function and they passed, however sr1 on the board was open.

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              • #8
                Serial number is KF949420

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                • #9
                  https://www.millerwelds.com/files/ow.../O436D_MIL.pdf

                  Here's the correct manual. That is not the SR1 I was initially looking at, as I suspected. But, if it's bad, that could definitely be all or at least part of your problem--that board controls the field current in the welder, which is the key to it all working. That's probably a $5-10 part if you can find a generic, and since there is no diagram for the board in the manual, the only way to do a generic is to have someone remove it from the board and see if they can find a part number on it. Otherwise, you're likely going to need a board and that may be 1.)impossible to find, and 2.)expensive if you can find it. Have any friends who fix electronics stuff? My concern is that it could have failed due to a shorted electrolytic capacitor, which would just blow the new one, too. I have not yet reestablished my electronics repair bench capability, so I'm sorry I can't be much help. At least I have all the equipment now, but it's in a pile waiting for a new bench/racks to put it all on, and unfortunately that's still far down my priority list.

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                  • #10
                    Well sr1, sr2, and sr3 are all open and seem to all be tied together through the F1 fuse and also tied to the PC board from what I can tell from looking at the manual. Thanks for that link by the way! Let me know how to proceed if you have any ideas. Appreciate the advice.

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                    • #11
                      I'm guessing it is very unlikely that SR1,2,3 are all open, and from a cursory look at the diagram, I doubt any of those being open would blow your fuse. (By the way, there appears to be an error on that diagram. There seems to be a wire missing from the right side of SR3--that terminal is floating. Does SR3 only have three wires on it in the machine?)

                      Anyway, You're looking at Find No. 3 on page 40 of the manual, right? I'm suspecting you are doing something wrong in the testing. Be sure they are not connected to the circuit--remove at least 3 of the 4 wires, (and obviously, mark 'em so you get 'em back in the right place). Each of the 4 diodes in the bridge should should show essentially a short -- 0 ohms or an ohm or two resistance in one direction, and virtually infinite resistance (open) (OL) in the other direction when you reverse the meter leads. Test each diode individually. The bridge terminals are generally marked--usually plus and minus for the DC output, and the other two sometimes marked AC. So put one meter lead on the + term and check with meter leads in both polarities to one of the AC terminals, then again to the other AC terminal. You have now checked 2 of the 4 diodes. Then, move a meter lead to the - term, and check to both AC terms again, reversing the meter leads for each diode. In all, you will make 8 separate ohms measurements. 4 of them should be very high/OL, and 4 should be 0 or close to it. If anything in that description is confusing, let me know. If one of those is bad, you can buy a replacement at Mouser.com, under mfr. part number GBPC4008 T0 They are $5.74 each and they have over 150 in stock.

                      Take a flashlight and see if you can see any markings or part numbers on that SR1 that's on the board. Can probably find one at Mouser for about $5 or less.

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                      • #12
                        Will update you on my findings as soon as I’m able to do the test. Thanks

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                        • #13
                          Well to answer your question about sr3 only having three wires to it, yes it does on this machine. I just performed the test you described and my results were inconclusive at best. Not sure if my multimeter is sensitive enough. I didn’t get any readings of zero or close to it. from the positive side of the terminals I did get an occasional high reading around 1900 in one direction against the ac terminals but it was an erratic reading that sort of jumped around. All SR1-sr3 tested the same. But I’m not real confident it was an accurate test. I may try cleaning up the terminals on those diodes and try the test again, bit of corrosion across all three.

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                          • #14
                            If that pcSR1 on my pc board is bad, could that be what is blowing the F1 fuse?

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                            • #15
                              I would certainly think so. Can't guarantee it without checking out the circuit, but if a diode in there is shorted, it would allow too much current through that circuit. Are you able to see any numbers or mfg. name on it?

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