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Thread: Quartz crystal wanted (non-standard value)

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    Default Quartz crystal wanted (non-standard value)

    Hi all,

    The wireless mic was dropped on the floor, and as a result, stopped transmitting. The mic is VHS, and it uses the internal Colpits oscillator based around the quartz crystal with the value of 21.1180 MHz to generate the carrier frequency of 253.3 MHz, which as you can calculate is 12-th harmonic of xtal.

    I have traced the fault down to the crystal - tried 20 MHz xtal in place of the suspect one, and the oscillator works happily, except the carrier is obviously way off now, and the base doesn't "hear" the microphone.

    Then I physically "opened" the xtal can with the junior hacksaw and found that the actual crystal inside is smashed (and NO! I did not break it while cutting the case open - it was already smashed!

    So, the fault diagnostic's pretty much complete, but that's where the "fun" begins...

    The manufacturer of the equipment don't have a service rep here, and electronics suppliers don't carry this value. So I am pretty much on my own :-(

    Anyone can help me with the replacement xtal of 21.1180 MHz ?

    Any other suggestions are also welcome.

    I could just buy another mic, but this one is good, pro quality, uses hardware compressor/expander, low-noise, etc. etc., so I am reluctant to part with it, at least until I absolutely have to...

    Thanks in advance, fellow Austechians,
    :-DS

    PS. I am in Sydney metro.



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    Junior Member Jalorathis's Avatar
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    Is it possible to send it back to the guys you bought it from?.

    I work in the AV business and deal with microphones each day. A couple of ours have broken (being beaten around a bit) and the supplier was happy to replace the transmitter section (not the head).

    Just as a matter of interest, what model mic is it.

    Jalorathis

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    Bright Star or HyQ will cut you a new crystal, doesn't cost that much either.
    Common xtals are cheap.

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    Senior Member vk6xlr's Avatar
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    Quote Originally Posted by digital_silence View Post
    I have traced the fault down to the crystal - tried 20 MHz xtal in place of the suspect one, and the oscillator works happily, except the carrier is obviously way off now, and the base doesn't "hear" the microphone.
    Why not modify the the receiver instead?
    Stay with the 20Mhz xtal in the mic and retune the base. If that's xtal controlled, put in a corresponding xtal.

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    2 Jalorathis:
    Bought it on ebay 'bout a year back. The brand is Enbao - made in China, but I suspect it's a copy of something more serious, as there are no shortcuts in the way the design is done: double sided PCBs, quality mic pick-up heads, separate outputs for each channel + master mix out, etc.

    I have emailed to Enbao in China - no reply so far.

    2 trash:
    thanx, will try this. Although, you need to specify parameters like parralel/serial cut, fundamental/overtone etc. which I wouldn't have a clue what they are (were... :-) for broken xtal...

    2 vk6xlr:
    You don't think I didn't think of that first, don't ya? :-)
    Nice idea, but it won't work as all bandpass RF-filters and LC-resonators are tuned to the 253.3 MHz original carrier (I can count at least 6 variable inductors and 3 variable caps). Same for the base, of course.
    And I've had a quick look at the base, and the only xtal I can see in the corresponding receiver channel is 66MHz, so I am immediately facing the same problem: (21.1180/20)=(66.0/F) => F is non standard :-)))


    Thanks everyone. Suggestion box is still open though.

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    Senior Member BCNZ's Avatar
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    Quote Originally Posted by digital_silence View Post
    Hi all,
    The mic is VHS
    You mean it is part of a VCR?

    I have emailed to Enbao in China - no reply so far.
    Don't expect one either. Stuff made in china is mass produced and so cheap to make, that if 1) they did bother to look at your email, and 2) could read and understand English - they'd probably send you a whole new unit. They wouldn't even bother trying to locate the crystal or the transmitter section of your mic - it's probably in a warehouse that's 3 km from the dude that deals with the emails and he's probably never even been out of his office or seen that building.

    As for the type of crystal, it will be a fundamental, then you need to look at the size of the case - take a look at Hy-Q's website - and check their data if you are not sure, but a QC49/U should do the job. You don't need to specify parallel or series cut - they will determine this based on the above information.

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    Quote Originally Posted by Studio1 View Post
    You mean it is part of a VCR?
    Typo, of course. I meant VHF.

    I asked one of my friends who speaks Chinese to call them and ask if they can send the replacement part down. We'll see what happens. Then I'll start talking to HyQ.

    Thanks.

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    Bright star are good... no need to worry about the specifics of the crystal cut... they know all that... you just tell them what the fundmental was, what harmonic is being used and if you can what sort of circuit it is in.
    I've had quite a few xtals made with them, I've never had to worry about anything more complex than that.

    I don't know about HyQ .. but if they're used to dealing with hobbiests, they'll be able offer the same services.

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