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Spectrum 2050 Pressure light on

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  • Spectrum 2050 Pressure light on

    I got a used 2050 from a guy that swore it worked fine for him (maybe). It seems to be in good shape, ICE-55C torch, decent consumables, the air filter is dirty but everything else was fine.

    The Pressure light stays on and the torch is giving lots of air but no plasma, the trigger on the torch does nothing to change the lots of air and lack of plasma. I jumped the pressure switch and nothing changes. I verified the inlet air pressure and the pressure in the system by changing the regulator in the 2050 and the one on my compressor. The voltage and amps it's getting is good.

    I'm just checking to see if there's any obvious fixes or diagnostic tests to narrow down my issue. The o-ring seems OK as do the rest of the consumables but I can look at changing them out, I just don't think that has anything to do with the issue.

    Any thoughts or ideas would be helpful. Thanks!

  • #2
    Do you have the manual? There is usually a top-level troubleshooting chart in all Miller manuals. You can find one here under SUPPORT at the top of this page. You'll need your serial number.

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    • #3
      The manual pretty much states that the only reason the light will be on is insufficient air pressure, which is definitely not the issue. I've given the machine everything from 20-165 psi, nothing makes the light go off.

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      • #4
        I'd give Miller Tech Support a call and see if they can help. They are generally really great at phone support. 1-800-4AMILLER and ask for tech support for plasma cutters.

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        • #5
          Jordan, I fixed one with a very similar problem. I can't say if it's the same problem, but if you have ruled everything else out (check continuity across the air pressure sensor, all other leak issues, etc.), then it could be issues on your main board. I will see if I can find my notes, but there were two chips (ULN2003 hex inverter, and I believe LM324) and the power resistors in the lower right that I needed to replace. If that is your issue, it will be a very tough fix without the Technical Manual.

          Before you tear into it, these have a very high/lethal buss voltage, so please ensure the big blue capacitors are discharged before checking anything.

          If you get through all of that, please post pictures of the main board - it's the rear board on the left side if you're looking at the panel. If there are any indications of heat in those lower right resistors, then you may have a similar problem. The ULN2003 I believe was almost smack in the middle of the board (a little lower and to the right of the plug for your air solenoid and air pressure sensor), and the LM324 is about 2-3" left of that chip. It's some years now, but I think this gets you close. Any signs of oxidation or heat on those chips and they're worth replacing.

          Hope this helps,
          Jon

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          • #6
            Jordan, I couldn't find my notes, but just looked at the schematic for the main control board. With everything off and ensuring the capacitors are discharged, find chip U2 - it should be just below and to the right of Plug/Connector RC-2. Remove the plug to RC-2. Measure resistance/diode drop from pin 9 to pin 18 and from pin 17 to pin 9. You should either have an open loop or diode drop. If it's zero resistance (or zero volts diode drop), then U2 is shot. Check diode D42 to see if it is still ok (open loop one direction, ~0.5V other direction). Either A3 or U5 was also giving me problems, which kept the Air pressure light on.
            Hope this helps,
            Jon

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            • #7
              Thanks for your help! I have 650mV diode drop on the D42 and from pin 9 to 18 and 9 to 17 of U2 its about the same, 625-675mV.

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              • #8
                Do you have the technical manual? I’m flying blind. I don’t even know what to test on A3 or U5

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                • #9
                  There did seem to be heat damage/discoloration in the lower right under R23.

                  edit: I just checked and R23 is a 150k resistor that is working correctly, around 130k on my multimeter
                  Last edited by JordanD; 01-04-2021, 12:45 PM.

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                  • #10
                    I am pretty sure those resistors sense the incoming voltage. They tend to run hot, every Miller board I have worked on that has them has signs of heat. The later Dynasty 200s kept the leads long and added more standoff, I am guessing to keep heat off the board.

                    The top middle connector is where the gas solenoid and indicator Leads plug in. They're all controller/affected by U2 and A3. Let me know when you've had a chance to look over the schematic and we can work through some board level troubleshooting.

                    Jon

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