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Thread: Quantar - No TX Transmit Audio - Fault SCM - SOLVED!

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    Thumbs up Quantar - No TX Transmit Audio - Fault SCM - SOLVED!

    I'm am VERY pleased to announce that I have found the fix for the TTN4094 Quantar Station Control Module TX audio problem. This happened to two boards with me and at least one other person that I know of. This may also apply to other SCMs that experience the same issue.

    Symptom: NO TX audio at all, not even PL on the carrier. Station will key up carrier but you never get any audio to pass.

    Cause: The offending IC is U306 on the lower right quadrant of the board (if BNC connector is to the left). This is a low pass filter through which all audio to the exciter passes after the D-A conversion process (all audio in the quantar is digitized). I found this bugger by soldering on test lines (using wire wrap wire) at the various stages before the audio leaves the SCM for the exciter. Using an O-scope, I found the chip where the audio went in but did not come out. All other voltages and clock signal checked good to IC U306.

    Fix: Order a Maxim MAX292EWE+ from your favorite supplier and replace it (cost about $12.46 USD). I used the clip all the leads off first, remove the chip, then clean up the solder pads technique. I hope you have a fine tip for your iron because you're gonna need it. If you have experience replacing surface mount components, this shouldn't be a problem. If not, you should probably practice on something else first.

    The picture attached shows the replacement chip in place. I have successfully performed this repair on TWO SCM boards.
    IMG_20130617_211958.jpg


  2. The Following 2 Users Say Thank You to mizzotch For This Useful Post:

    uplinker (Feb 16, 2015)

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    Excellent info! I replaced a bad SCM last December with this exact symptom. I've passed it on to the owner of the bad board.

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    Well done.
    It is a fine thing to be honest, but it is also very important to be right

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    Hi friends
    I have found the fix for the CLN6960C Quantar SCM Tx audio problem too but the offended IC was the U309.
    This IC is placed at right from U302.
    U309 is a Tx audio signal multiplexer and send the audio to digital potenciometer U311
    I`m happy to share this

    Regards

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    uplinker (Feb 16, 2015)

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    Excellent on finding a fix for another version of the same problem. I have two 6960 boards I believe but so far, they work fine.

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    I have a CLN6961C SCM which just recently failed while switching between analog and P25 modes.
    There is no response when using Analog mode at all. When using P25 there is a carrier only, no audio. I suspect the same problem as above. I'm from downunder and I'm having problems sourcing a Maxim MAX292EWE+ IC. I have priced some up from NJ, costing around $200 in shipping!
    Would someone have one to spare and who would ship at a more reasonable price?
    Thanks.

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    http://www.digikey.com.au/product-se...ords=MAX292EWE

    $8.43 AUD + $34.00 shipping, or...

    http://au.mouser.com/Search/Refine.a...word=MAX292EWE

    $9.96 AUD + $39.00 shipping.

    Both vendors have free shipping if you buy at least $200 worth of stuff in total (easy to do with either of them.)

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    Thanks. I have been to Jaycar this afternoon and they have the MAX292CWE IC's available, $70 for ten. Can the CWE be used in this application in place of the EWE? I see the difference is the temperature spec's between the two.

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    If the only difference is the temperature range, it will probably work. I ended up with the EWE because it was the closest part number I could find to the original with easy availability. What's the temp range on the CWE and EWE?

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    I just did one, went from no audio to all good in 60 seconds! Good find for sure !