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D104 Mic/Amp Transistors...Gone Bad?!?

Discussion in 'General CB Services Discussion' started by Robb, Mar 3, 2009.

  1. Robb

    Robb Yup

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    So, I bought a D104 from eBay and wired it up for the standard Ranger/Magnum arrangement. Popped a new battery in it an plugged it in. Key it up and it is making noise and acts like the contacts on the leaf switch are dirty. Fine. So I get a thin, fine file and clean off the contacts a little bit. Presto; no more intermittent key-up. But now, there is another problem.

    It appears that the mic can talk, but the modulation is way, way low - even when turned up all the way in the mic. And the radio mic gain is way up - too. I'm beginning to wonder if the transistors in this thing are gone - because there is no gain from the mic. Are the 2N2712 transistors known for failing - or is there another problem with this mic I haven't yet tracked down. Additionally, I also went over all of the solder joints on the amp board to make sure there weren't any bad joints. I'm wondering if I overlooked anything - or do these transistors in this mic have a history of going bad.



    Anyone know?
    #1

  2. fnkycoldmedina

    fnkycoldmedina Well-Known Member

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    very rare for the amp to go out .you probably have a bad head element.if you know someone with a working head ask to borrow it for a test.
    #2
  3. MisterFatty

    MisterFatty Poppin Fresh!

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    You didn't mention what stand it is, Some of the TUG9 stands have a Choke on them, you may want to check it if it does. I also have an early Silver Eagle that has the same choke as well.
    #3
  4. Robb

    Robb Yup

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    Right.
    It's a TUG9 stand w/6 conductor cable. It has the lazy key on it; the very reason that I bought it - sorta like a Silver Eagle in that respect. I don't have another mic head to see if the element has failed.
    What is the significance of the choke? The schematic doesn't show one; although one part on the board itself looks like a choke. What's up with that?!?
    #4
  5. MisterFatty

    MisterFatty Poppin Fresh!

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    [​IMG]


    My schematic does not show it either, this one originally had some yellow coating over the wire, it looks a bit messy, I hand wound it, I messed it up a bit taking the board out for the pic.. May not look great but it works fine, before I rewound it the audio was extremely low...
    #5
  6. Robb

    Robb Yup

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    What was the specs on the rewind? Is there a microhenry equivalent?!?
    I'm spent three hours working on this mic, and got it working - without the modulation like it should be. Why did Astatic leave it out of the schematic? SHould I just remove it and put a jumper in its place?!?
    #6
  7. packrat

    packrat Active Member

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    It was pretty common for people to bypass the amp circuit on the mic for use with radios that didnt need an amplified mic. Make sure that wasnt done on yours. it usually meant moving the white audio wire on the board directly to the mic plug wiring.

    PR
    #7
  8. fnkycoldmedina

    fnkycoldmedina Well-Known Member

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    rob,i wouldnt mess with anything until you try a new head.i rarely ever see the mic amps go bad .and i have had dozens of 104`s.if need be for a quick test take the head off,find an old mic element ,take the 2 wires from the element and put them in the holes in the top of the stand .the stand will amplify anything you can plug into the head jack,so if you can plug in an old stock mic element or something you can quickly find out if the stand is indeed amplifying.
    #8
  9. Robb

    Robb Yup

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    Yeah; it was the mic element.
    I had an old D104 handheld mic that I took the element out of w/the capacitor and put it in the TUG9 stand .
    It will now 'heavily' modulate; but I'm not quite sure how it sounds on the 'other end'.
    I can't use the talkback feature on the radio - because it feeds back way too easily...

    1) Should I leave the capacitor off/on?
    2) Where can I find a replacement element for the TUG9?????
    Last edited: Mar 4, 2009
    #9
  10. fnkycoldmedina

    fnkycoldmedina Well-Known Member

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    rbmicro.com sells nice replacement element kits,complete with mounting foam and everything neccessary to do the job .they get great reviews.they are 25.00 bucks.

    or a good working used head can cost more.
    #10
  11. C2

    C2 Well-Known Member

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    I've been able to repair a few. You might get lucky and find the baffle has come loose or something else similar.
    #11
  12. C2

    C2 Well-Known Member

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    This might give you an idea

    DATING the ELEMENTS
    #12
  13. Robb

    Robb Yup

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    Hey, thanks for that link C2. I actually took apart that crystal element that failed, it was a delicate surgery. Put it all back together and it still didn't work; I thought I did a pretty good job - really. It tests on a ohmmeter at 2.5 mega-ohms; but still modulates very poorly for some reason. The D104 handheld element is working great, but it doesn't fit like the original element does. So I used some foam to locate it and center it. The number on the old, bad element is 'MC 320'; sure would like to find an original that still works. Even the replacement elements are only 2" in diameter, and the original element is 2 1/2".

    The handheld mic also has a capacitor on the back; I left it on. But - doesn't that cap tune the frequency response of the element? I tried it with it off, but - of course - I can't tell what it sounds like on somebody else's radio. I'll keep it for now; but if anyone has a good replacement 2 1/2" element - please shoot me a PM - I would like to buy it...
    #13
  14. fnkycoldmedina

    fnkycoldmedina Well-Known Member

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    keep your eye on ebay ,but even a replacement head or element can be 30-40 dollars.sometimes you can get lucky and pickup a whole mic for the money.but getting a good head is a lucky shot at best unless the seller says its works good.

    tell ya what..i got a whole stand for sale for 50.00 shipped......i,ll sell just the head for 30.00 shipped if you want it .thats the whole head element and all.

    i like paypal.for a look at the head check the for sale section under redone tug8 stand.pm me if you want the head.
    #14


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