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Thread: W3 HHCH whining noise

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    Default W3 HHCH whining noise

    Does anyone have the SRN for the ASTRO Spectra (or early XTL) W3 HHCH whining audio fix? I used to "sort of" fix these years ago by shielding the audio line, but it only half worked.

    I recall an ancient SRN where the problem was discussed and a transistor was removed or something along those lines. If anyone has the SRN and is willing to post it, that would be fantastic. Thanks!


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    Is your alternator, or heater motor creating the whining? Just was reading a Midland Syntech service manual and they have a chapter on reasons for whining from auto electrical systems. Problems with bonding the battery, the chassis and the vehicle body were suggested. The noise introduced via the ground wire.

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    Itís a problem specific with that microphone. It does it on battery, out of vehicle. Well known problem.

    https://forums.radioreference.com/mo...um-repair.html

    Thatís not the right way to do it. I recall the removal of a transistor, but again, I canít find the SRN.

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    Found this in our archive!

    http://communications.support/comsup..._pla_1297.html

    But no pictures... Sounds like a grounding issue on the cartridge. I'll see what I can do and report back.

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    Well, that didnít fix it. Running a ground to the negative output of the mic element, permanently keys the radio with hot audio.

    Running the ground to the casing of the element, causes the radio not to power up.

    Face palm.

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    Are you already connecting the cable shield (black wire on HHCH end of cable) to chassis ground?

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    FWIW, this is a quote from a guide that was created by our member Alpha:

    "One other thing worth mentioning is a known issue with the HHCH having problems with the microphone cartridge position and/or the routing of the wires from the mic pellet to the PCB connector picking up noise from the microprocessor inside the HHCH. The issue shows up as a strange background noise during transmissions that is a continuous drone that varies in sound from a low growl to a strange sort of train locomotive sound, it’s difficult to describe but easy to hear when it mixes with PL and it sounds awful. This can be solved in two ways, I found pulling the mic cartridge back a tiny bit from it’s full forward position in the rubber cup it sits in helps, or re-routing the wires away from the IC they lay across can help. I have also heard replacing the wires with a short length of shielded audio type co-axial cable can help too. To adjust the mic position you have to operate the PTT and listen with a monitoring receiver while you jockey it around to find the best position. If you move to too far back from the hole where the audio enters, the volume will suffer so there’s a happy medium to strive for."

  8. The Following User Says Thank You to Number 6 For This Useful Post:

    Mars (Feb 12, 2018)

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    Yeah, moved the wires around (before I posted the thread). It did get rid of a majority of the whine, but I still have some noise. Was hoping for a permanent cure, but no such luck.

    If anyone has the original SRN with pictures, archived, that would be great. I have the HMN4044D version -- so no transistor removal required, but it would still be nice to have the full SRN for future purposes and the benefit of other members

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    Quote Originally Posted by Number 6 View Post
    FWIW, this is a quote from a guide that was created by our member Alpha:

    "or re-routing the wires away from the IC they lay across can help.
    I have also heard replacing the wires with a short length of shielded audio type co-axial cable can help "
    Did you try the "shielded cable" approach (or have before)?

    I am not sure how well this would apply, but in installing card-access, the cable run from the reader would use shielded cable but the shield would only be grounded on one end to avoid ground loops.
    So grounding it one one side may be worth a try, as you can't ground the mic anyway
    Quote Originally Posted by Mars View Post
    Running the ground to the casing of the element, causes the radio not to power up.


    As you did get some results from moving the wires, perhaps other shielding can be applied.
    If it is the micro-processor creating noise could a nickle-paint or copper foil be applied to the surface of micro's package (and grounded)?

    Something more elaborate would be a mylar copper sheet barrier (grounded) as an overlay between the board components and mic wire.
    Locally, a copper tape roll is 2" x 50' / $23.
    Or "craft size" foil sheet at Michaels.