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Thread: Possible problem with IC-735 receiver?

  1. #1

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    Question Possible problem with IC-735 receiver?

    My ICOM IC-735 has been working OK for several years, but I have hardly used it as I didn't have a decent power supply.
    Last week, I finally got one. I hooked up the radio and... nothing!
    A symptom of the fault seemed to that on power on, there is burst of regular noise from the speaker, but then it fades to nothing and the needle of the S-meter moves fully to the right.
    I pressed just about every button, clicked every switch and twiddled every knob, but to no avail.

    A couple of net searches later, I thought I had found there answer. An thread from some other forum indicated that the problem could IC8 (CD4021) in the PLL circuit had died. So, I replaced it.

    The problem is still there.

    While poking around a bit more, I slid the "RF GAIN" slider all the way and the needle returned to the left and the regular radio noise came back. Moving it up and down, the receiver goes dead and the needle moves.

    The panel that has the RF GAIN, also has the NB LEVEL, VOX GAIN & DELAY and MIC GAIN.
    it has seven equally spaced white lines running horizontally across it.
    The receive operation seams OK with the RF GAIN slider from the top to the fifth line. Below the fifth line, the receiver goes quieter and the needle moves to the right, finally totally silence at the bottom. Slowly moving the slider up, the noise starts to return around the fifth line and back to normal at the top. If I move the slider quickly, it still takes a few seconds for the noise to return and the needle to go left.

    Any ideas?

    Thanks & best regards,

    Rob

  2. #2

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    Personal suggestion, go tho this link, https://www.icom.co.jp/world/support...WT=No&INQWORD= , download the manual, and start from scratch. I did this with my 757gx and found some very interesting things that assisted with setup and running the transceiver. 73s. God bless and good day.


    KD9KVS


    I have a brain injury.
    I am not my brain injury.
    This does not define me.

  3. #3

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    It's also OK on FM and seems to TX OK.

  4. #4

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    Quote Originally Posted by OH8GAD View Post
    My ICOM IC-735 has been working OK for several years, but I have hardly used it as I didn't have a decent power supply.
    Last week, I finally got one. I hooked up the radio and... nothing!
    A symptom of the fault seemed to that on power on, there is burst of regular noise from the speaker, but then it fades to nothing and the needle of the S-meter moves fully to the right.
    I pressed just about every button, clicked every switch and twiddled every knob, but to no avail.

    A couple of net searches later, I thought I had found there answer. An thread from some other forum indicated that the problem could IC8 (CD4021) in the PLL circuit had died. So, I replaced it.

    The problem is still there.

    While poking around a bit more, I slid the "RF GAIN" slider all the way and the needle returned to the left and the regular radio noise came back. Moving it up and down, the receiver goes dead and the needle moves.

    The panel that has the RF GAIN, also has the NB LEVEL, VOX GAIN & DELAY and MIC GAIN.
    it has seven equally spaced white lines running horizontally across it.
    The receive operation seams OK with the RF GAIN slider from the top to the fifth line. Below the fifth line, the receiver goes quieter and the needle moves to the right, finally totally silence at the bottom. Slowly moving the slider up, the noise starts to return around the fifth line and back to normal at the top. If I move the slider quickly, it still takes a few seconds for the noise to return and the needle to go left.

    Any ideas?

    Thanks & best regards,

    Rob
    There is nothing wrong with your radio. This is normal operation for the RF gain control. If you have the operation manual, see page 11. Otherwise you can download it from http://www.icom.co.jp/world/support/...pdf/IC-735.pdf.

    From the manual: "This control varies the gain of the RF stage when the transceiver is in the receive mode. Slide the control upwards for maximum gain. Note that as the control is slid downwards, the 'S' meter needle rises, and only those signals stronger than the level indicated by the needle will be heard. In the FM mode, regardless of the control setting, the RF gain is fixed at the maximum."


  5. #5

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    Read.
    The.
    F***ing.
    Manual.

    How dare you sir! I'm an engineer, to suggest such a sensible course of action is heresy!

    Many thanks for that - to be honest, I had never noticed it before and I'm pretty sure I have played with all the knobs, buttons and twiddly bits before.
    Most embarrassing!

    Again, thank you!
    Last edited by OH8GAD; Mon 22nd Apr 2019 at 08:05.

  6. #6

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    rofl.gif I hate it when that happens! rofl.gif

  7. #7

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    Quote Originally Posted by OH8GAD View Post
    Read.
    The.
    F***ing.
    Manual.

    How dare you sir! I'm an engineer, to suggest such a sensible course of action is heresy!

    Many thanks for that - to be honest, I had never noticed it before and I'm pretty sure I have played with all the knobs, buttons and twiddly bits before.
    Most embarrassing!

    Again, thank you!
    You're welcome.

    I have an iCom IC-751A and I thought what you were describing was very similar to the way my radio works. I usually leave my RF gain all the way up unless I am trying to reduce noise, but dialing it back also reduces the incoming signal, so it's kind of a Catch-22.

  8. #8
    K7KBN's Avatar
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    When I was in Radioman school (USN) in 1963, one of the instructors was talking with our class about electronics. He commented that we should keep track of the students in HIS class to see how many of them were "engineers" in five or ten years. Then came the question from somewhere in the back of the room: "For which railroad, Chief?"
    73
    Pat K7KBN
    Semper ubi sub ubi.

  9. #9

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    Talking

    Quote Originally Posted by K7KBN View Post
    When I was in Radioman school (USN) in 1963, one of the instructors was talking with our class about electronics. He commented that we should keep track of the students in HIS class to see how many of them were "engineers" in five or ten years. Then came the question from somewhere in the back of the room: "For which railroad, Chief?"
    :'D

    I went to a British Merchant Navy Radio Officers' college frok 1988 to '90. From the mid-80s onward, I think less than a quarter go work at sea. One was even a sheep farmer in NZ for a few years! The closest I got to "electronics afloat", not including deploy buoys, was building and commissioning an environmental monitoring station on a raft on a small lake in northern Finland...

  10. #10

    Default

    Quote Originally Posted by K7KBN View Post
    When I was in Radioman school (USN) in 1963, one of the instructors was talking with our class about electronics. He commented that we should keep track of the students in HIS class to see how many of them were "engineers" in five or ten years. Then came the question from somewhere in the back of the room: "For which railroad, Chief?"

    Quote Originally Posted by OH8GAD View Post
    :'D

    I went to a British Merchant Navy Radio Officers' college frok 1988 to '90. From the mid-80s onward, I think less than a quarter go work at sea. One was even a sheep farmer in NZ for a few years! The closest I got to "electronics afloat", not including deploy buoys, was building and commissioning an environmental monitoring station on a raft on a small lake in northern Finland...
    I was a US Navy Quartermaster (navigation specialist) before i became a diver. My only exposure to radio prior to going to Vietnam was collecting weather messages from the Radiomen and an occasional use of the bridge-to-bridge radio. I really learned tactical communications on patrol boats in Vietnam, and that helped prepare me for more of the same in the Reserves when I came home and also for a stint as a police dispatcher.

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