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Miller Maxstar 150 STH no Current with Remote Plugged In

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  • Miller Maxstar 150 STH no Current with Remote Plugged In

    Hi,

    I have a Maxstar 150 STH, SN LH080234M, that works fine without the remote in both Stick Mode and Lift Arc Tig mode. However, it doesn't seem to want to increase current with the remote plugged in. The HF will arc, but current only picks up once in a dozen tries. It's the same with lift Arc and the remote plugged in - it works once in a dozen attempts. I confirmed the resistances from the foot pedal leads are correct and the welder output voltage is correct with the remote plugged in. The leads for the amperage control have continuity between PCBs 2 and 3 as well. Is there something I am missing in my troubleshooting?
    Thank you,
    Jon
    Last edited by jjohn76; 11-28-2018, 01:26 PM. Reason: My apologies, I meant good continuity on the leads between PC3 and PC2, not through PC2 onto PC1.

  • #2
    Hey Jon,

    So if you call miller on this unit the first thing they will likely ask is if you have performed pre-power checks (I know I know, it powers up but this is also good for checking vital components/circuits individually). If you have completed a pre-power check, to me, the next steps are as follows:

    1. Rule out pedal/verify pedal is sending the correct control voltage command signal back to the Maxstar. (be sure to check for the correct Ohm range at the plug itself it at all possible to rule out the control cable.


    2. If step 1 has been completed then now it's time to verify that a 0-10V signal is being sent to PC3, the command signal goes through that PC3, and PC2 before getting back to PC1. I am not seeing a break down of PC1 or PC2's receptacles so I am not sure how you have verified that there is continuity through those boards as there are no miller provided breakdowns on the ribbon cable that goes from PC1 to PC2 at least that I am able to find).

    Because there is little to no information on testing the command feedback where it gets back to PC1, I would call miller to get the pins on the ribbon cable (RC1) on PC1 and verify if you are getting a 0-10V command signal back to PC1 with the pedal. beyond that I would attempt to rule out PC3 itself.


    Millers tech help # 920-735-4505 EXT: 3 for tech help.

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    • #3
      Thank you! I called Miller Tech last week, but didn't get much help beyond PC2 is likely bad. I will try again tomorrow.

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      • #4
        PC2 is most likely the problem. I've seen it at least 5 times. I've even seen it on newer models. Not a terribly expensive fix.

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        • #5
          Thank you! I had a feeling it was with whatever input buffer is on PC2 or PC3. I will try to put together the schematics and trouble shoot the circuits this weekend and post what I find.

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          • #6
            I just finished going back through PC2 and PC3, with all passive components and diode checking out. The foot pedal wiper leads went to the LF347 (all surface mount), which I am assuming is the input filter to the microcontroller. After dusting the boards and putting the welder back together, all works without issue. Glad it is fixed, I was about to create the schematic for the multi-layer surface mount input boards, which looks like it would have been a bear.
            Thanks all for the help!
            Jon

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