FT767 no receive on CW USB or LSB

Discussion in '"Boat Anchor" & Classic Equipment' started by G7BGV, Jun 10, 2021.

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  1. G7BGV

    G7BGV Ham Member QRZ Page

    Hello
    This is my first post on here and I am currently restoring a Yaesu FT767GX whihc is giving me headaches.
    I had no display at first which I resolved with a replacement display board. This gave me most functionality back on the radio however USB LSB and CW do not seem to be receiving anything. I get static on FM and AM. Can anyone point me in the right direction as to where i should concentrate my efforts

    Kind regards

    Chris
     
  2. W9GB

    W9GB Ham Member QRZ Page

    54BDCABE-5AC0-4076-A0A7-A6F289E47D83.jpeg
    Chris -

    FIRST, Before “Swapping Parts ALWAYS CHECK your AC to DC conversion.
    Too many follow that method — THEN destroy the New Part due to DC Voltage problem.

    Internal Switch Mode Power Supplies (SMPS) used in many Japanese radios of that period
    the Yaesu FT-736R was VHF-UHF cousin (shares some parts/designs).

    Yaesu FT-767GX Technical Manual (Italy), 152 pages
    http://www.iw2nmx.it/Yaesu/FT-767GX/FT-767GX Service Manual.pdf
    ==
    Gary Sawyer, KO6WB provided advice on FT-767GX in April 2012 (QRZ Tech Forum - Archives)
    https://forums.qrz.com/index.php?threads/ft-767gx-no-tx-on-hf.343144/

    The Power Supply (PS) unit in the Yaesu FT-767GX is a bit unusual.
    The pass transistors are on the negative lead of the 24VDC power supply.
    Still, if you do not have 24VDC … check the Power Supply.

    You will need the FT-767GX Service (Technical) Manual. It's at; http://www.scribd.com/doc/37250775/Yaesu-FT-767GX-Technical-Supplement-Service-Manual.
    It's not the best copy, but it will help in troubleshooting.
    — Gary
    ===
    Weston Electronics of Concord, GA has Suspended Amateur Radio repairs
    http://www.westonelectronics.com/body_repair_services.html
     

    Attached Files:

    Last edited: Jun 11, 2021
  3. G7BGV

    G7BGV Ham Member QRZ Page

    Gary
    Many thanks for the reply. I have already recapped the PSU and checked voltages which are correct. I have display and I get noise on AM and FM but not on other modes. Encoder is a little jittery but usable. I have the documents you linked to but this is quite a complicated radio and I am struggling to isolate the problem. If I inject a modulated signal at the antenna I can hear it on AM and FM but not elsewhere. I thought it might be the SSB detector but replacing that had no effect.
    Regards

    Chris
     
  4. KI4ZNV

    KI4ZNV Ham Member QRZ Page

    So you know the LO is working and the front end is at least kind of working because you can tune in a signal generator signal.

    First thing with all these radios is to clean all the switches with deoxit or cramolin! They are just as flaky as old rotary switches if the radio has been left.

    Next step is to get out the scope and start tracking the signal down from the front end through the IF strip and into the detector. Is there a BFO operating into the detector or is there no BFO signal? Start at the beginning and work step by step to the end.
     
  5. G7BGV

    G7BGV Ham Member QRZ Page

    Many thanks for the info I know a little but not sure about checking the BFO what’s the best way to do this, will it show up on the scope or do I need an RF probe?
    Chris
     
  6. KI4ZNV

    KI4ZNV Ham Member QRZ Page

    Oh yeah, it should show up on the scope nicely. Really, anything you can do with vtvm and an RF probe, you can do just as well with a modern scope and a 10X probe.
     

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