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Thread: Need VHF Astro Spectra Schematics (100w)

  1. #1
    tim No Longer Registered

    Default Need VHF Astro Spectra Schematics (100w)

    Hi Folks,

    I've got an Astro Spectra that's gone deaf. Looks like it may be either
    the switching diodes, or a bum RF amp.

    Anybody have a soft copy of the schematics?

    I've got both a Low band and VHF antenna on the back deck of my
    car... guess the LB fried it. Gonna move the antenna!

    Thanks,

    Tim


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  3. #3
    tim No Longer Registered

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    Thanks a lot!!!

    Tim

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    Tim, were you recently servicing the radio?

    A common mistake, which will lead to the symptom you're describing, is when one plugs the two coaxes from the PA brick into the wrong jacks (reverses them) on the RF boards. It's not a fatal (i.e. smoke) mistake, but it causes no RX or TX. Radio will not show any error codes, either.

  5. #5
    tim No Longer Registered

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    Hi Mars,

    I wish it were that easy!

    No, I just noticed that some of the repeaters weren't as
    strong as they used to be.

    As I have a second antenna on the trunk lid of the vehicle,
    I believe that coupling between them zapped something in
    the front end of the spectra. It's been suggested that there
    is a pin diode in the front end.

    I've got it apart, and will start doing the debug this afternoon.

    Interestingly enough, I have another vehicle that also has a
    low band and high band antenna relatively close, and a similar
    thing happened to an XTL2500 (VHF also). However, there were
    obvious burn marks on that board.

    Thanks again!

    Tim

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    Nothing like front end overload .

    It will be the pin diode CR353. I have seen the rf amp trans Q354 go but not often. Usually to kill it you need to short out the antenna top a txing radio.

  7. #7
    tim No Longer Registered

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    Hi Notarola,

    It turned out to be CR3903, the pin diode on the PA board (feeds the RX).

    Couldn't believe it.... I looked at an analog Spectra manual, and they used the same part! Guess that stash of old 'goodies' came in handy!!

    Now it's doing something else... when I 'de-key', the carrier goes away, but then comes on for about 100ms. A kind of double key. But, if it is scanning, it doesn't do that!

    Does it on all channels.

    Anyhow,

    Thanks!!

    Tim

    Quote Originally Posted by Notarola View Post
    Nothing like front end overload .

    It will be the pin diode CR353. I have seen the rf amp trans Q354 go but not often. Usually to kill it you need to short out the antenna top a txing radio.

  8. #8
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    Could it be doing a post-MDC ID, maybe? Also could be contact bounce in the microphone, I have a mobile mike that double keys on release almost every time. Try a different mic, maybe?

  9. #9
    tim No Longer Registered

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    Hi Alpha,

    Well, that was it.

    I wouldn't have thought that was it, as when it was in the scan mode, it didn't do it.

    So much for logic! haha

    Now to see if I can fix the mic.

    Thanks a bunch!!

    Tim

  10. #10
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    Hehe, cool, glad to help!

    Try increasing the return spring tension, and cleaning the switch contacts a bit wouldn't hurt...

  11. #11
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    Isnt that always the way you fix one thing and something else happens. Reminds me of fixing CTRs you replace the on/off button and the customer complains that everything is now blueish.