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Thread: Realistic DX-390 repair help

  1. #1

    Default Realistic DX-390 repair help

    I've got a Realistic DX-390 I've had for about a year now. I misplaced the plug in adapter I had been using and tried a new one. upon doing so there was a "pop" so I immediately removed it. I later found the correct one and plugged it in but now there is no sound. The buttons still "beep" when pressed but no sound comes out of the speaker. I tested the speaker and its not blown. I imagine that "pop" was the sound of something being blown but what? I'm pretty good about soldering/repairing things I jus don't know what to be looking for to replace. any help would be greatly appreciated.

  2. #2
    Join Date
    Jan 2008
    St. Mary's County Md since 2000


    On general principles, the first likely suspect is that the plug was in backwards and that perhaps a polarity protecting diode blew.

    Look at the circuitry immediately close to the power input for a diode to check!

  3. #3


    It sounds like you used the wrong power adapter
    (too much voltage, improper polarity, or AC instead of DC)

    This radio (circa early 1990s) is not a good one for a beginner to " start poking around".
    You will spend more $$ to get tools, documentation materials, and parts -- than the radio is probably worth.

    At a minimum you will need schematic and/or service manual (contact Radio Shack, if they have).
    IF you are lucky, the damage is limited to the radios power supply section -- blown regulator or diode.
    Nullius in verba

  4. #4
    Join Date
    Jan 2011
    Houston Texas


    It most likely pop-ed the audio output.

    The key beeper is a different sounder device.

    W9GB offers some good info, that will help you.

    Live and learn, we all learn the hard way, and hopefully never make the same mistake twice.

    A fuse should have saved it from reverse polarity, but one must be used before it will do any good.

    Good Luck on your project.

    "Theory only works perfect in a vacuum." KA9JLM Don

  5. #5
    Join Date
    Feb 2004
    Bakersfield, CA


    Well the good news is there is a reverse polarity protection diode on the power in connector. The bad news is, if the unit you used was stronger than the diode and the diode opened then the reverse voltage would be applied to the circuits. Okay, the other problems that you have not covered, like does the display show a tuning frequency? Does the frequency change with the tuning? If you put the radio on a known frequency that has a broadcast station on it does it show on the S-meter? These things will help to narrow down how much damage has been done.
    The service manual for the DX-390 is available for free at;
    Hope this helps

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