Icom IC 735 Repair

Discussion in 'Radio Circuits, Repair & Performance' started by N8CMQ, Aug 1, 2017.

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  1. K6LPM

    K6LPM Ham Member QRZ Page

    Keep up the good work fellows! I always loved the 735, Great little radio. I have never ran into the encoder problem but do have two radios that need to do the trimmer caps and alignment. Projects om my back burner since a new 7300 is now the rig in use here.
  2. N8CMQ

    N8CMQ Ham Member QRZ Page

    Thanks all!

    K6LPM, I can do the mod and update at a reasonable cost, but shipping is probably going to cost more if you are interested in having it done,
    but I would look for someone local to do it if you don't want to do it yourself.

    N1FPZ, Yes, that is the encoder I plan on using, but I am going to use a 14049 hex inverter instead of discrete transistors. I built a proof of concept
    with an old track ball mouse that had just the right encoder. It had the inverter chip installed, and I re-purposed the circuit to provide buffering and
    inversion of the signals. I call it my external VFO... With the ENS1J-B28-L00256L encoder, a piece of perf board and the hex inverter, I should be
    able to get the radio working and still look the same. If you just hook up three inverters in series, take the A and Anot, B and Bnot signals off the
    second and third inverters, it should work like my track ball encoder does. At least, that is the plan!

    K8AI, thanks for the offer, so far I have a handle on the unit... By the way, I love your antenna farm!

    At least I hope I do! Last night, I tried to transmit, but there was no power out.
    I did see a signal on my spectrum analyzer, so there is something is going on, but I bet it will be something simple, as most of the problems have been.
    The unit had a bunch of intermittent receive problems, the one I found last night was the main board RCA receiver connector had failed. I replaced it
    with a panel mount connector and ran wires to the board. That should help keep the mechanical force from breaking the solder joints on the board.
    But I got tired and pulled the plug... There is always tomorrow to continue! Beside, I want to change the electrolytic caps on the main board now,
    while I wait for the new encoder to arrive.

    N8CMQ Jeff
  3. N8CMQ

    N8CMQ Ham Member QRZ Page

    Great news! I have transmit!

    I worked Tennessee and Maryland with 100 watts on 40 meters. Got a 58 and a 57 with it.
    Todd in Tennessee was also running 100 watts. He reported it sounded very good.

    I had to spray the power out pot and mic gain pot to cure an intermittent transmit problem.
    I also got a new state for WAS as well!

    For the next operation, I will be replacing the electrolytic caps on the main board.

    N8CMQ Jeff
  4. N8CMQ

    N8CMQ Ham Member QRZ Page

    I have been using the 735 with the track ball for frequency control, and I am beginning to like it!
    The tuning rate is a bit slow, as the encoder is not the right pulse count, but I manage with it as is,
    but it makes using the radio and the computer a little confusing, I sometimes change frequency
    when I want to move the cursor on the screen...

    I need to toss it on the repair bench and finish the cap change! ;)

    N8CMQ Jeff
  5. K6LPM

    K6LPM Ham Member QRZ Page

    Thanks for the offer... I probably will eventually do it myself. My main holdup is a specialized highly needed part or actually a tool or gizmo whatever ,,, called "round tuit" .... once I get one of those I am going finish alotta projects!!!
    Ya know one of the two 735 rigs I have was D.o.A. when I got it... the other needed a power switch and caps. Looks like someone else was already inside of it and probably caused other issues with the PLL board, looks as if batt was replaced and shoddy solder job....Hmmmmm? Wonder if maybe I should or could part it out for parts... Or even maybe send off two broken radios and send back one good radio.... hmmm Got a 757 GXII also that Yaesu also used plastic trimmers in and is having issues. Yeah gotta lotta projects.
    #1 is finishing my tower and f12c4xl antenna erection! yup def need more round tuits to get anything done around here.... I am telling ya! Fersure!
  6. N8CMQ

    N8CMQ Ham Member QRZ Page

    Hey Brian, I found a round tuit, but I used it last night replacing the electrolytic caps on the main board!
    I`m not sure if I am seeing a difference or not, the band conditions were not good last night.
    I didn`t see any leakage from these caps, so it might have just been practice I got from replacing them. But better safe than sorry tho!

    N8CMQ Jeff
    K6LPM likes this.
  7. N8CMQ

    N8CMQ Ham Member QRZ Page

    Well, last night the bands were good!

    I was on 20 meters and made a contact or two there, but not many people noticed, as they didn`t
    check 20 meters? Most every one was on 40 meters, as I expected, and 40 was hopping till the
    band got jammed by some high powered jamming station.

    The radio was working well, the big difference I saw was with the pass band tuning and notch filter
    operation. The noise blanker does not seem to work, and if a high power station is nearby, the signal gets clipped and makes more noise than it suppresses...

    When I get a replacement encoder and install a shorter cap on the main board, I will be able to put
    the covers back on!

    N8CMQ Jeff
    KE8EZZ likes this.
  8. N8CMQ

    N8CMQ Ham Member QRZ Page

    News update!

    I cured a very severe noise problem with the radio.

    I looked on my spectrum analyzer and I could see the noise with the antenna
    plugged in to the analyzer, but I could hear the noise in the radio without the
    antenna plugged in, so I thought the noise was in the radio.

    I ended up turning off power to the house to verify the noise was in my house,
    then I ended up in the shack pulling plugs till the noise quit.

    I had a battery charger plugged in behind the radio for my drill/driver,
    and it was causing noise in every ham band I had, and in the active region
    for every band I was using...

    Once I unplugged it, all of the bands cleared up, and I can hear so many more

    You would have thought it had a jammer built in covering my used frequencies...
    I will tear into it and see why it is killing my reception.

    N8CMQ Jeff
    K8AI likes this.
  9. K6LPM

    K6LPM Ham Member QRZ Page

    Jeff, been enjoying hearing about your adventures with that little 735. As I said earlier,,, I have alot of affection for that little radio. Even in this day and age it still pulls its weight and it shows that you are getting a great amount of bang for your buck with all fun it has provided just as a project if nothing else.
    We are right there with you with every update we are living vicariously through your posts. Fine Business!
  10. N8CMQ

    N8CMQ Ham Member QRZ Page

    Thanks! That and my education is why I like doing it.

    Not to mention all the contacts I have made with it.
    Now if they would all QSL via eQSL and QRZ, I would
    be much closer to WAS!

    N8CMQ Jeff

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