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FT-736r 430mhz problem

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K7CNT, Oct 25, 2017.

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  1. K7CNT

    K7CNT Premium Subscriber QRZ Page

    Hi everyone, I could use some help with my 736. Problem is with tx pwr 430-449 section. Very little pwr out 430 to 440, zero out at 430 but starts putting out as you go up in freq, and at 440 pwr starts to climb up to around 5 watts maximum @ 449 mhz. The alc is nil (on the radio meter) under 440 mhz, but alc starts coming up as you go up in freq and peaks at a reading of 3 on the radio's meter @ 449 mhz.

    Things I have changed:
    swapped out the 430 rf board
    Installed a new final PA module M57745 unit

    All the PS voltages are good to the boards
    the 13.79 mhz signal is making it to the RF board
    Listening to the output on a receiver in FM mode the signal sounds fine, good audio.
    I don't get proper voltage readings or alc meter readings when going through the TX adjustments per the service manual.

    Seems like an ALC issue. The service manual is not helping me much. Please help if you can.

  2. W9GB

    W9GB Ham Member QRZ Page

    John Klewer, N6AX in Plaentia, CA is very good with Yaesu FT-736R VHF/UHF transceiver.
    He should be helpful for eventual repair or restoration, he formerly worked at Yaesu Service.
    WA9SVD likes this.
  3. WA9SVD

    WA9SVD Ham Member QRZ Page

    I'll also put in a vote for John N6AX. He's done work for myself and many of our club members in So. Cal, and I've not heard a single complaint. He works (or at least tries to) on all makes and models, not just Yaesu or iCom..
  4. W2GDJ

    W2GDJ Ham Member QRZ Page

    I know this was a while ago but did you ever find out what was going on. I have gone the same route as you. I even replaced the driver transistor before the 430 brick. Still erratic output. If I key down on CW mode the output starts at around 5 to 8 watts. Then it will go over 30 watts output with the ALC jumping all over the place. Maybe I need to drop the radio from the second floor for a fine adjustment.

    Dave W2GDJ
  5. K7CNT

    K7CNT Premium Subscriber QRZ Page

    I replace the encapsulated rf power module for the 430/440 unit and it came back to life. Just dumb luck

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