ICOM IC-706 Filter Board HAM Radio Repair

This is an overview of a typical radio repair. Please note that this is not a tutorial. Any questions welcome.
Video Rating: 4 / 5

/23 Comments/by
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23 replies
  1. John Hawkes
    John Hawkes says:

    Hi Steve, The early ICOM 706 MK1 had a low TX audio path problem i.e.
    sounded quite) which could be fixed by replacing the negative feedback
    resistor to a higher value on the first stage audio amp IC. I am not aware
    that the MK2 had this problem (May be the same). Check R236 by IC22 on the
    Main Unit Board, if it is 27K then replace it with 82K. later versions of
    the 706 were fitted with 82K resistors also the MK2G has the same mic amp
    configuration also fitted with 82K, I hope this is of help.

    Reply
  2. thebakerman1
    thebakerman1 says:

    Excellent informative video here. I know I greatly appreciate info like
    this, as it can help people understand how their radio’s work and why (or
    why NOT in this case).

    Reply
  4. SteveMinto1
    SteveMinto1 says:

    Hi John I have track another local ham member down with a ic-706 and tried
    his fist mic off his ic-706 on my radio. It turns out that the fist mic I
    have even though it looks an original I am told is in fact a copy. Using
    his mic all the radio TX audio reports come back good! John call me sad but
    I have watch all your video’s. You are so professional in showing care and
    consideration in the radio’s you work on. If ever I need a rig doctor I
    know where I will go. Kindest regards Steve.

    Reply
  5. TheOritek
    TheOritek says:

    Schematics shows individual filters with 2 relays each driven in parallel.
    HY1 coil is 1Kohm, 2 in parallel are 500 ohm. A shorted coil or the diode
    across it would read low. Unsolder one coil pin on the two relays and check
    coils. If you measure 1Kohm for two coils in parallel then one coil or its
    driver is open. Unsolder one of the two relays coil pins and test which is
    open. Shorted or open coil might kill the driver transistor.

    Reply
  8. John Hawkes
    John Hawkes says:

    Hi. To be honest I am no longer in a position to take in repairs. ICOM UK
    in Kent will turn this around for you quickly I am sure at a sensible
    price. This is a very common fault. I hope this of help. Best Regards John

    Reply
  9. SteveMinto1
    SteveMinto1 says:

    Hi great video John! I have bought a icom ic-706 mk2 Please help i am
    getting very poor audio reports compared to the same contacts with my Yaesu
    FT857. The icom’s mic gain is full up I get radio reports of 5 on the Yaesu
    but only 2/3 on the icom? Please tell me if this is a common problem? If so
    what would be the best thing to rectify it. Also in your knowledgeable
    opinion minus the 70cm whats the best radio Yaesu or icom? Thank you for
    any advice in advance. Only M6 Kind regards Steve

    Reply
  12. George Smart
    George Smart says:

    I have exact same fault with my IC7000. The rig does 100watts on 24/28MHz,
    but on others, it losses power in the filter (I think). Can you offer some
    insight into how you found the faulty drivers? My relays all look fine, and
    there are no obvious blown diodes. I am a competent engineer, but given the
    similarity here, it seems obvious to ask for advice where it’s available.
    Thanks, de M1GEO.

    Reply
  15. John Hawkes
    John Hawkes says:

    Hi George, sorry for the late reply. I does sound like the filter board is
    not switching correctly. To be honest I am not that familiar with the 7000.
    The problem with the 706 is that one of the 6M filter relays stays switched
    in causing the problem. Regards John

    Reply
  16. John Hawkes
    John Hawkes says:

    @MM6ISM Yes it’s a common fault with the 706’s however; I am sure that 11
    meters is OK for the filter board. Outside of these bands causes problems.
    If you use one of these radios it would makes sence to keep the power down..

    Reply
  17. John Hawkes
    John Hawkes says:

    Hi, Sorry for the late reply. I have changed the workshop around a few
    times since making this vid. Basically the RF output goes into a 50R dummy
    load and I use an RF sniffer to feed the analyzer so not to exceed the max
    +30dBm / 1W input. I also use RF attenuates with the spectrum and setup the
    offsets for tacking measurements . To be honest when looking at RF output
    power I am only really interested in the second harmonic differential as
    this gives an indication of the state of the LPF.

    Reply
  18. barry frith
    barry frith says:

    Hi. I also have the 706 mk2 with an output problem. On FM TX it only has 20
    Watts output on all bands. You can also hear a loud buzz from the fan on TX
    if you turn the output up. Turn it up to 30 or 40 Watts and the radio dies
    until you unkey then it comes back to life. Audio is clean on fm but
    scratchy on ssb above 20 Watts. Got any ideas mate..?

    Reply
  20. mykedindeal
    mykedindeal says:

    Could you please detail the test setup?like outputfrom transceiver has a
    50ohm 100W dummy load which is conected to the spectrum analiser and
    frequency meter via a 50ohm bnc cable…etc Thank you

    Reply
  21. Alex Baker
    Alex Baker says:

    Hi there, good to see a fellow enthusiast with the right mind & gear. I
    have a ic-706 here with the symptoms of no TX,RX between the bands of 22MHz
    – 30MHz. I have narrowed this problem down to the filter board & would seem
    that the correct relays are not energized to complete the filter path for
    this band. I removed Q8 for testing & I cannot find this transistor
    defective. Have you come across this problem with this model for radio
    before? Any help would be appreciated.

    Reply

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