Yaesu FT747GX Repair

Discussion in 'General Technical Questions and Answers' started by VE3YFB, Jan 9, 2018.

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  1. VE3YFB

    VE3YFB Ham Member QRZ Page

    I am presently visiting St. Petersburg area and wonder if there are any Hams out there that do repairs to Yaesu FT747GX Transceivers. My problem is that when I tune the digits jump all over the place, I cannot tell what frequency I am actually on. From what I understand this can be caused by malfunction of the Optical Encoder (which I have difficulty finding one) or also told it could be Capacitor problems. Anyone out there can fix this for me. Also maybe someone has an old Yaesu I could get some parts from ? Winston VE3YFB
  2. N3DT

    N3DT Ham Member QRZ Page

    Might be easier and even cheaper to find a used 757GXII or similar. Should be able to find one for a few hundred bucks that works. I've got a 757GX that's still working, I thought about selling it, but use it for an alternative rig. It's fine for what it is. Actually I still like it. Just as sensitive as my TS2000 and a lot simpler to work. Works fine with my AL80B too.
  3. KM4HGU

    KM4HGU Ham Member QRZ Page

    Clairmont Skyland. (Located in Gainsville GA.) They have repaired both my FT757GX, and my FT757GXII. They do a very good job, and are reasonable.
    There are very few places in this country that will even consider looking at the older SS Yaesu rigs.
  4. W9GB

    W9GB Ham Member QRZ Page

    Yaesu FT-747GX Technical Supplement (Service Manual)
    http://w5jgv.com/downloads/FT-747 Technical supplement, A3.pdf

    The Rotary Encoder on tbe Front Panel is mounted to Display Unit Board # C029432AA
    Turn to Service Manual, for details about Display Unit Board.

    Page 12 : Display Unit Parts Layout (component and solder side).
    Page 13 : Schematic Diagram (Shows rotary encoder used is a 3-wire design: CLK, DATA, GND).
    Page 37 : Parts List. S3001, Q9000394, Rotary Code Switch (Rotary Encoder)

    Yaesu FT-747GX Rotary Encoder (S3001)
    You can clearly see this was a mechanical encoder (~24mm square; common size in 1980).
    700FCEA4-1B7E-4C86-BBCF-1B6735497D28.jpeg 75D6E6D4-3447-4A61-A877-4D64F79BE8E7.jpeg

    Repair and Modifications to Yaesu FT-747GX (2010, German web site)

    Yaesu FT-747GX Rotary Encoder Replacement
    by TA3LKU , November 2017

    CAUTION: There are a Wide Variety of Rotary Encoders, in different sizes and specifications.
    Wikipedia - Rotary Encoders
    Last edited: Jan 28, 2018
  5. W9GB

    W9GB Ham Member QRZ Page

    TRX Bench
    Program #7 : FT-747GX Rotary Encoder Replacement, Part 1

    Program #8 : FT-747GX Rotary Encoder Replacement, Part 2

    A few Notes, about this video.

    1.) Original Rotary Encoder was mechanical and had Detents. I believe it did NOT have a Push Switch function. In overall size, it is similar to the Bourns EPS series, a Contacting (Mechanical) encoder that is 24mm square.

    2.) TRX Bench Replacement Encoder is Bourns EM14 series : Rotary Optical Encoder w/Switch
    The EM14 series is 14mm square (size) and features Metric and English versions,
    with a variety of shafts (1/4” or 6mm; slotted or flated), PPR, and Detent.

    Specific Part number used: EM14A0D-24 L064N73
    Mouser web page

    3.) A 3-wire mechanical rotary encoder does NOT require DC voltage source.
    When you switch to Optical, you require a DC source (usually +5 VDC).
    He notes using terminals 1, 2, and GND on new Optical encoder.
    He did not mention where he tapped +5 VDC on the Front Panel PCB.

    4.) Rotary Encoders are Common and Plentiful due to Production/Process industries,
    as well as User Interface for thousands of electronics appliances.
    WATCH the Resolution Specification (stated in PPR, pulses per revolution),
    Critical to matching frequency movement per revolution (processor programmed).

    5.) There are likely Better Replacements, that do not require Drilling knobs for wider shaft diameters. Just a matter a taking time for doing the Parts Research.
    Since 1980, Rotary Encoders have become smaller in size and majority are Metric (6mm) with 1/4” (English) still offered by some models.
    Last edited: Jan 28, 2018
  6. W3ZF

    W3ZF XML Subscriber QRZ Page

    Not sure if I should start a new thread on this one. My faithful Heathkit SB-1400 (the rebadged FT-747) started experiencing a subtle drift during FT-8 activity (see attached) which renders that mode rather useless! The other subtly annoying thing is that the ability to RETAIN the memories has gradually deteriorated over time; I even wired an external battery holder OUTSIDE of the radio to make it easier to replace the voltage source...but eventually it appeared to even drain a AA cell battery rather quickly. I am a technically challenged amateur...not afraid of a soldering gun but lacking sufficient diagnostic knowledge to accurately troubleshoot the circuit intelligently to know what "hornet's nest to poke at", hi hi. Any suggestions? OTHERWISE, the radio works swell for all other modes.[​IMG]

    Attached Files:

    Last edited: Feb 21, 2020
  7. N2ZD

    N2ZD Ham Member QRZ Page

    The 747 is a radio plagued with cold solder joints, also by now it's a good idea to start recapping the radio. I've had many of them, dry caps are probably all of your problems related to failed memory and battery consumption.
  8. N2ZD

    N2ZD Ham Member QRZ Page

    I may have a spare encoder contact me by email.. Regards Richy N2ZD

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