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Superstar JA - no TX Issue

Discussion in 'CB Radio Modifications' started by Robb, Dec 7, 2017.

  1. Robb

    Robb
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    Yup

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    Similar to the President Jackson.
    Radio just up and quit TXing one day for no apparent reason.



    PLL is locked; has full range from bands A-F. Tested TR31, 32, & 33 and are OK. Receive is OK. Voltage reg good. Caps are good/replaced. Mic audio coming thru the speaker when keying the mic; no roger beep can be heard tho.

    Thoughts? I've researched and found nothing useful so far. Need some advice/help!

    C'mon gurus, techs, and hobbyists alike - give it your best shot!

    http://malzev.tripod.com/cb-radio/block_ja.gif

    http://www.cbtricks.com/radios/president/jackson/graphics/president_jackson_pb-042_sch.pdf
     
    #1 Robb, Dec 7, 2017
    Last edited: Dec 7, 2017

  2. sp5it

    sp5it
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    Master of puppets

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    Tx led goes red?
    Mike
     
  3. Robb

    Robb
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    No; the green RX led just switches off - as it should.
    Thanks.
     
    #3 Robb, Dec 7, 2017
    Last edited: Dec 7, 2017
  4. sp5it

    sp5it
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    Must go red on tx unless is broken led or tx/rx switching is not working.
    D61, D59?
    Mike
     
    #4 sp5it, Dec 7, 2017
    Last edited: Dec 7, 2017
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  5. Robb

    Robb
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    D60, 61, & 59 all tested good.
    So did D49/zener.
     
    #5 Robb, Dec 7, 2017
    Last edited: Dec 7, 2017
  6. sp5it

    sp5it
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    Look at the schematic. You miss 8V on red led. Bo backwards and see where is disappears.
    Mike
     
  7. sonoma

    sonoma
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    I bought 2 of these when they came out. one quit TX right after I got it. on mine the coil wire back at the back of the radio by the finals had a cold solder joint and was not letting the radio TX. you could check the solder joints back there to see if that is what quit.
     
  8. Robb

    Robb
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    Sonoma: There is no switching to TX, so there isn't any feed to the driver/final.
     
  9. ExitThirteen

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    With the solder side of the radio facing up, check the front left corner of the board for cold solder joints, and also check D69 for voltage. Sounds like you're losing voltage to that corner of the board. That area has your roger beep circuit in it, as well as your +8V rail. I'd do the old chopstick method, press and poke around that area and see if you can get it to fire up. Also check the pins on the 2SA473 (TR501) and see if you get ~12V in, and ~8V out.


    ~Cheers~
     
  10. nomadradio

    nomadradio
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    Time for a sniffer.

    Set a second radio to the same channel, ANL off, volume turned up. Connect a coax jumper to the sniffer radio. At the far end of the jumper, thread the connector shell back from the plug body, and slide it back the coax. The center pin of the plug is now a half-inch long sniffing antenna. See if it can pick up a transmit signal starting at the TA7320 transmit-mixer chip IC8. It should get stronger as you move the sniffer down stream toward the driver transistor.

    If you hear nothing, it's time to check the inputs to IC3 the transmit mixer. This is a chip that almost never goes bad, so you'll want to 'scope pin 6 for the 16 MHz PLL output, and pin 2 to see if you have the 7.8 MHz IF feeding it.

    As a rule, if there is any 27 MHz energy at all coming out of IC3 pin 9 the sniffer radio should hear it.

    73
     
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  11. Robb

    Robb
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    No amount of prodding gave results. D69 has 8v on it. Gonna retouch several more solder joints - tho. Already did a bunch.

    Seems that it just isn't switching to TX. Will take some voltage readings tonight. No voltage chart to work with . . .

    Haven't tried sniffing yet; but I'm almost certain that the problem is in the TX/RX switch. So far - no dice.
     
  12. sonoma

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    ROBB if you will PM me your email address I have a service manual that has the voltages on it. they are in a different language but you should be able to check all the parts for correct voltages. that portion is in the english language. I have used it to align my 2 Jackson radios. it is is to make out what they have printed out to do the alignment with it.
     
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