FT747 drifting frequency

Discussion in 'Radio Circuits, Repair & Performance' started by MI0OIM, May 12, 2019.

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  1. MI0OIM

    MI0OIM Ham Member QRZ Page

    Hi folks

    I've had this rig and been very happy with it for 6 years or so.

    99% of the time spent on CW

    but recently, it has started to drift off frequency. Usually after 15 minutes or so after being switched on. The pitch of the received signal rises as if I was tuning.... not enough to disappear, over maybe 5 seconds, and then drops back sharply.

    I know that there are similar issues with other Yaesus of a similar age but I can't find a vid on youtube where the 747GX is addressed

    Looking at the nearest I can find..... could it be the CW adjuster that's on the back panel beside similar for USB and LSB?

    I don't want to wade in a break stuff!

    any wisdom, gratefully received!

    Thanks
     
  2. G3YRO

    G3YRO Ham Member QRZ Page

  3. MI0OIM

    MI0OIM Ham Member QRZ Page

    Thanks for that, but I don't think so.

    closer to this.......



    the similar component on the 747 is on the back facing board with external access, three in a row labled CW LSB & USB.
     
  4. G3YRO

    G3YRO Ham Member QRZ Page

    Well does it only do it on CW? Or on SSB as well? (if it does it on SSB then it's NOT the cw carrier oscillator jumping)

    I've personally never come across a crystal oscillator jumping like that . . . but you could have a "tired" crystal that is playing up (sometimes air gets inside the can and causes issues)

    Roger G3YRO
     
  5. VU2NAN

    VU2NAN Ham Member QRZ Page

    The problem, which may arise on any of the modes, is the result of corrosion of contacts in the plastic trimmers TC 01, TC 02 & TC 03 located on the 'Local Unit' board (marked 'CW', 'USB' & 'LSB' on the rear panel).

    The solution is to replace all three with ceramic trimmers. Alignment is to be done as described in the Yaesu FT-747 Technical Supplement.

    73,

    Nandu.
     
    PU3PSF and AI3V like this.
  6. MI0OIM

    MI0OIM Ham Member QRZ Page

    great stuff! thanks.
     
  7. G3YRO

    G3YRO Ham Member QRZ Page

    I guess this was a cost-saving that Yaesu used on later rigs . . . they always used to use ceramic trimmers back in the day on rigs like the FT101 . . .

    Roger G3YRO
     

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