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YS-500 power/swr meter problem

Discussion in 'Radio Circuits, Repair & Performance' started by K1LPI, Dec 25, 2013.

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  1. K1LPI

    K1LPI Ham Member QRZ Page

    My YS-500 rf power/swr meter is acting a bit odd. The forward power and swr functions are working correctly. But, the refelcted power reads the same as the forward power. I downloaded the schematic and can't see anything that could cause this. The diagram does not show the details of the rf coupler. Any suggestions?

    Dave
    K1LPI
     
  2. W9GB

    W9GB Ham Member QRZ Page

    The Germanium (1N60, 1N270, or 1Sxxx Japanese equivalent) or Schottky diodes (BAT41, BAT46)
    are most common passive component that fails in the Coupler / Sensor Assembly of these meters.

    Daiwa (japan) has basic circuit for these simple RF sensors (3-wire output: Forward, Reflected, Earth/Ground)
    http://www.qsl.net/4/4x6on/RADIO MANUALS/DAIWA/DAIWA--CN-410-CN-460-user Manual.pdf

    Schematic diagrams of RF/SWR meter sensors can be found in almost any ARRL or W6SAI/Jones Radio Handbook

    OHR WM-2 QRP Wattmeter Manual (Doug DeMaw, W1FB(sk) design) -- schematic at back.
    http://tracey.org/wjt/temp/wm2.pdf
     
    Last edited: Dec 26, 2013
  3. KH2G

    KH2G Ham Member QRZ Page

    Are you testing this into a dummy load? The SWR may be reading correctly

    Dick KH2G
     
  4. K1LPI

    K1LPI Ham Member QRZ Page

    Yes, I am using a dummy load. The swr reading is low as it should be. That's why this is so puzzling. If the coupler was damaged, bad diode for example, I would expect a high swr reading even with the dummy load. I guess I'll have to pull it apart to see the coupling circuits and test the diodes.
     
  5. WB8TCB

    WB8TCB Ham Member QRZ Page

    Dave,

    Has this meter always acted this way, or is this a recent development. The reason I'm asking is that there is an error in the schematic diagram for that meter. What you're describing is exactly how the meter would act if the unit is wired as shown in the schematic diagram available at:

    http://www.foxtango.kc9foz.com/Eighties/YS-500.pdf

    The "C" (common) and "REF" (reflected) wires are reversed on the "FWD/REF" switch. If the unit is actually wired correctly (as opposed to the schematic), then I'd look around that switch, and also around the wiring that is external to the coupler, to see if there is something awry in one of those areas. Since the SWR function is working correctly, I have doubts that you'll find anything wrong with the circuitry inside the coupler.

    Phillip, WB8TCB
     
  6. K1LPI

    K1LPI Ham Member QRZ Page

    Hi Phil, I'll take a look at the wiring. It has acted this way since I received it but it is a used meter so I can't say what it did before I got it. Were any of them shipped with the wiring error initially? It doesn't look like any work has been done to the wiring as it looks original.

    Dave
     
  7. WB8TCB

    WB8TCB Ham Member QRZ Page

    I don't personally know of any of these meters being miswired from the factory, but I'd look carefully to see if yours was. I have also run across two other schematics from Yaesu with a minor wiring error in the diagram, but I do know the equipment was properly wired at the factory.

    I have, however, run across this same issue with Kenwood where not only the diagram had an error, but the units from the first manufacturing batch actually were miswired.

    Phillip, WB8TCB
     
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