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Autek WM-1 - stuck in 200W scale?

Discussion in 'Ham Equipment' started by Big Kahuna, Feb 21, 2021.

  1. Big Kahuna

    Big Kahuna Sr. Member

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    I've been wanting one of these for years and just purchased a used one and was told it was working and received it today and it is working but the 20/200/2000 watt switch doesn't seem to do anything. Regardless of the switch changing it seems to be stuck on the 200W scale.



    On the plus side - it seems to be giving very accurate readings on the 200W scale but it's kind of useless to me without the other two settings.

    Just wondering if anyone else has run into a similar issue? The owner died so there is no customer service any more. I'm hoping maybe it's just a faulty switch?

    Any other suggestions on what to check is very appreciated.

    http://bama.edebris.com/download/autek/wm1/Autek WM-1 Watt Meter and schematic.pdf
     
    Slowmover likes this.

  2. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    I have two of them, awesome meters for sure. I have not had that problem, and the only thing I can think of is the obvious switch malfunction. Thanks for the link to the information.
    Chris
     
    Slowmover likes this.
  3. nomadradio

    nomadradio Analog Retentive

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    Looking at the schematic, a bad scale-selector switch that just won't close a circuit should put it in the 20 Watt range all the time. The power scale is selected by the negative-feedback resistor on the input section of U1, a LM348 opamp chip. The 20 Watt scale puts the highest-value resistor in this spot. The 200 position puts another resistor in parallel with it, and the 2000 scale puts a lower-value resistor in parallel with it.

    The scale selector would almost have to be stuck with the middle-position circuit closed all the time for it to get stuck set for 200 Watts.

    P.S. I think I see an error in the reverse-engineered schematic posted at BAMA.

    Maybe more on that later.

    Maybe.

    73
     
  4. Big Kahuna

    Big Kahuna Sr. Member

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    Yeah it’s strange the switch has zero effect, even switching while keyed it doesn’t even move a hair, just stuck on 200W scale. The switch feels functional, and it seems unlikely it would get stuck in one position on this type of three way sliding switch.

    SWR may not be working properly as well, only seems to move to the correct position when radio hits peaks and then readings seem low (comparing to my other meter).

    Oh well, can’t win them all, when buying used there’s always that risk.
     
    Slowmover likes this.
  5. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    I have an autek that took a lightning strike, coupler is bad but the mechanical parts are still probably good
    Let me know if you interested in it for parts, it is yours for cost of shipping.
     
  6. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Can you pop it open and take some pictures? Maybe somebody will spot something out of place. Maybe the switch failed and someone hot wired it for 200w mode?
     
    Slowmover likes this.
  7. Big Kahuna

    Big Kahuna Sr. Member

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    The seller ended getting back to me and was very nice and is going to accept a return.

    Since they aren't cheap I decided I'd rather get the cash back and try to find a working version than risk having one with issues.

    Thank you everyone for the help!
     
  8. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    As a side note, one oddity about the power socket on the back is that the center pin is negative. At least on the two that I have.
     
    Robb and Slowmover like this.
  9. Slowmover

    Slowmover Elmer

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    And I blame everyone for their glowing reports of this cool piece of gear.

    Good luck on second go-round.
     

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