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Cobra 142gtl alignment no tp16?

Discussion in 'General CB Services Discussion' started by Wizard68, May 8, 2018.

  1. Wizard68

    Wizard68 New Member

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    Sams says connect osciliscope to tp16 ( L18 secondary) there doesnt seem to be a tp16. Where do i find the L18 secondary?


     

  2. sonoma

    sonoma Sr. Member

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    refresh my memory, for some reason I do not remember the step for a TP16. . all I remember is a TP10 for this radio as far as the highest TP number. even searched my files for the 142 and did not find where it shows to test at TP16.
    I use the trc-450 to align my 142 radios.
     
  3. Wizard68

    Wizard68 New Member

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    Screenshot_2018-05-08-12-06-41.png Screenshot_2018-05-08-12-07-06.png
     
  4. Wizard68

    Wizard68 New Member

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    Its the 2nd step
     
  5. Wizard68

    Wizard68 New Member

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    I found L18 no problem but cant find tp16 ive looked on all the circuit trace pages and schematic till my eyes are bugging out......
     
  6. sonoma

    sonoma Sr. Member

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    I have never had the sams manual for the 142 radio. I have always used the service manual for a trc-450 for alignment. it shows tp10 to adjust L18. .
    surely one of the other guys will show up and have some feedback for you. I have seen several items over the years wrong in the Sams manual so not telling if it is right or not since I never had the Sams for this one.
     
  7. kaos513

    kaos513 Well-Known Member

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    Is it a china model?
     
  8. nomadradio

    nomadradio Analog Retentive

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    Best way to peak L18 is to watch the signal level at pin 17 of the 8719 PLL chip. This prevents the probe's capacitance from affecting the adjustment.

    L18 is not connected directly to any receiver or transmit circuits, so you can't just peak it by watching transmit power or the S-meter.

    73
     
    Klondike Mike likes this.
  9. Handy Andy

    Handy Andy Active Member

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    Would this help?

    Cobra142L18TP16.gif
    It's similar to the TP for 1st IF on a Cobra 25...

    By my recollection - R126 stands upright... by L18.

    142GTLL18.jpg

    Delicate...yes...

    Just frustrated that this radio is gone out of my collection ...

    GEMTRONICS has got a similar chassis -

    Got help from someone whom used to work for Robyn back in the days to help me "tune" this way...

    Regards!
    :+> Andy <+:
     
    #9 Handy Andy, May 8, 2018
    Last edited: May 8, 2018
  10. Robb

    Robb Yup

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    If you have the Sams manual; then there should also be a page that shows where the TP is on the chassis. But Nomad already nailed it; if you can find it.
     
  11. Wizard68

    Wizard68 New Member

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    First of all i want to thank everybody for the great feedback. You dont realize how much i appreciate it. And yes nomad im going to use your technique to see how that works out. So i went over the schematics again and i cant believe it.... low and behold sitting there all by its lonesome self is tp16 connecting to the secondary side of L18.
     

    Attached Files:

  12. Wizard68

    Wizard68 New Member

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    No its a taiwan model
     
  13. kaos513

    kaos513 Well-Known Member

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    k thanks.
     
  14. kaos513

    kaos513 Well-Known Member

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    he must be using different alignment as i have sams and do not see tp16
     
  15. Wizard68

    Wizard68 New Member

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    Im just going by what it says....its a sams photofact for the 140/142gtl base
     

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