HF radio equipment: When to diagnose/when to replace

Discussion in 'Wireless & RF Design' started by chisel, May 4, 2009.

  1. chisel

    Thread Starter New Member

    May 5, 2008
    8
    0
    Could any experienced Radio Amateurs, repair technicians or just knowledgeable persons who contribute here, kindly weigh in on the following?

    I have an HF (Radio Amateur) transceiver with a particularly puzzling fault.
    Sometimes it will fire up and run ‘to original specs.’ without a single issue over as many hours as one decides to test. On other occasions, upon hitting the power switch, the meter will light up but the radio will not emit a single sound or function in any way.
    I cannot induce the fault when it is functioning normally or coax it out of an inoperative state when it is in that ‘mood’. I refer to thorough routine checks such as looking for loose connections and seating and unseating connectors and so on. (No point in pretending that I pulled out a service manual and started looking for where voltages should be etc.)

    My questions are: In your experience, does this indicate that the equipment should be replaced?
    Would this be a standard recommendation in the repair trade based on years of experience?
    If so, is it because the components or the connections to them are deemed unreliable and not cost effective to diagnose?

    I look forward to your kind comments.

    PS: - The transceiver is the Icom 745
     
  2. RAH1379

    Well-Known Member

    Dec 13, 2005
    69
    1
    The first place i would look is the fuses, make sure they are tight in their holders, a loose fuse can cause this. I would also check the solder joints with a magnifying glass and the traces on the circuit board for very tiny cracks. Those usually show up by gently flexing the board from two opposite sides first, then the other two opposite sides. You can also try a hair dryer, it could be a cap that works when its warm but not when its cool. I am not sure if it has a linear power supply or a switching supply, but if it is a linear supply you can disconnect circuits to see if one of them is shorted and loading down the supply. If it microprocessor controlled scope the voltage going to the processor to make sure it has no ripple and is 5 volts, it should be within about 1/10th of a volt.Sometimes a small electrolytic at the power supply pin with develope a small leakage and cause the microprocessor to fail to run. I would expect those checks to narrow it down. If it has a switching supply, you cant remove the load to test it, those need a load to run, they will usually run from about half the load resistance on up but it depends on the supply.
     
  3. RAH1379

    Well-Known Member

    Dec 13, 2005
    69
    1
    By the way, i would never throw out an icom radio as hopeless unless it was melted into a blob. Let me know if you get more info, i am sure you can get it working, just don't give up, and don't stress out, and you will get it.
     
  4. chisel

    Thread Starter New Member

    May 5, 2008
    8
    0
    May God bless, RAH1379.

    You used discernment and read beyond my questions. Your Post-Script confirms this and I'll say no more in that regard.

    The trouble-shooting tips are much appreciated.
    The 745 is microprocessor controlled and the power supply is the switching type - an Icom peripheral.

    I'll get to work on this soon, and thank you for the kind words of encouragement.

    I am obliged.
     
  5. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Also use Google to look for known problems with the specific radio.
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,646
    2,345
  7. radiohead

    Active Member

    May 28, 2009
    474
    31
    have you contacted Icom to see if they had any similar problems with that model XCVR? I would advise you to go straight to the manufacturer to see if they have any suggestions. If it's new enough, it may still be under warranty. Replacing SMT components requires much practice, patience, skill and the right soldering equipment (tips, wattage rating, temperature, etc).
     
  8. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    Indeed, these are good suggestions. I found a power supply that was sitting on the shelf for so long that it wasn't working. When I took the fuse out and put it back in, it worked to some extent (had some other problems). Make sure you dont have any frayed wires that are shorting and that you dont have cold solder joints. A multimeter will come in handy during your troubleshooting!
     
  9. radiohead

    Active Member

    May 28, 2009
    474
    31
    Then again, it could be as simple as corrosion on the battery contacts or bad batteries.
     
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