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Power Supply for MFJ-989D

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W3MAT, Aug 13, 2021.

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  1. W3MAT

    W3MAT Ham Member QRZ Page

    OK to power MFJ-989D antenna tuner with 13.8VDC 23 amp regulated supply Samlex SEC-1223? I have one my two meter rig is on.

    An aside. I need to get this antenna tuner onto the bench and check it over. It took some lumps getting here. Terrible packing job. Maybe the bent, bottom case corners (all four), will have acted like shock absorbers.
    Last edited: Aug 13, 2021
  2. W1FBV

    W1FBV Ham Member QRZ Page

    I would think so, but you are overdoing it. All the power does is light the lamp in the meter. A linear wall wart is all you need.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    Any 12-15Vdc source is fine. Current draw is <100 mA
  4. W3MAT

    W3MAT Ham Member QRZ Page

    OK thanks on volts and amps.

    Thought it also powered the meter circuit. (Not just lamp.)

    Supposed to -- or have to -- have 9V battery, too?
    Last edited: Aug 13, 2021
  5. W3MAT

    W3MAT Ham Member QRZ Page

    Looking at schematic. Seeing switch 103A and 103B. Single throw double pole or something I guess

    I saw the note in the manual about the manufacturer wanting you to have a battery in there to avoid having the battery leads 'free to move around and come in contact with any parts that move or conduct current.'

    I take it you don't 'have to' have a 9 volt battery in there. As long as you make provisions for keeping those battery leads from coming in contact with anything.
    Last edited: Aug 13, 2021
  6. W9IQ

    W9IQ Ham Member QRZ Page

    No problem at all. Just make certain to put an appropriate low amperage fuse in the circuit. If you fail to do that, the 23 amp supply is more than capable of setting off a nice smoke and fire display in the event of a cabling or tuner problem.

    - Glenn W9IQ
  7. W3MAT

    W3MAT Ham Member QRZ Page

    Good idea. Like a 5A on the positive lead. Or if less what amperage rating?

    Matthew here.

    Edit: 5 amps is probably too high. It was just what I had in a spare holder. I have some 1 amp and 0.5 amp fuses on hand (250V).
    Last edited: Aug 14, 2021
  8. K8JD

    K8JD Ham Member QRZ Page

    Got a Wall Wart around ?
    A half amp 12V wall wart would probably power the lamp. New ones are about 5 bucks and I have a basket full of them used and working.
    I power two MFJ tuner lights and a cooling fan here, with them.
    Ran an MFJ Cub QRP radio with one. .
  9. W3MAT

    W3MAT Ham Member QRZ Page

    Wall wart is original design. Of course I have a few. Cannot throw anything away. You would think I grew up in the Depression.

    I'd just as soon not plug one more thing into the wall or power strip.

    I think it's not just the lamp that gets powered here. Not a big current draw -- as was said earlier -- however there is a meter circuit board in this model and I think it gets powered by the supply. Like at Q101 and Q202
    Last edited: Aug 14, 2021
  10. W3MAT

    W3MAT Ham Member QRZ Page

    Correction: Q101 and Q102.

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