IC- 706 won’t transmit

Discussion in 'Radio Circuits, Repair & Performance' started by KM6QPL, Nov 28, 2019.

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  1. KM6QPL

    KM6QPL Ham Member QRZ Page

    I have a IC-706, I got for some motivation to pass my general exam so I have something to look forward to after passing. I received the unit yesterday evening hooked it all up and attempted to use the 2 meter capability as that is really all I can use at this point with it. After a few minutes it became apparent that the unit will not transmit. It can receive fine but will not transmit anything. I tried different power settings and different antennas same results.

    Any suggestions on what I’m doing wrong? Or who might be able to help me fix it?
     
  2. WR2E

    WR2E Ham Member QRZ Page

    What kind of antenna are you using?

    How do you know it "won't transmit"?
     
  3. KF4ZGZ

    KF4ZGZ Ham Member QRZ Page

    Too vague.
    I suggest trying simplex in the middle of the band.
    Make sure you are on the right antenna output for vhf.
    Make sure the faceplate is securely seated ..... maybe even very, very, gently clean the contact points with
    a pencil eraser. Do this with all disclaimers ......:rolleyes:
     
  4. KB3UWC

    KB3UWC Premium Subscriber QRZ Page

    I would see if it will transmit on side band on 2 meters also check fm on 6 meters you really need a dummy load. If it dosn't transmit on 6 meter fm. The 706 is known for a problem with a trimmer in the fm transmit vco circuit. Have a look at this web page.
    http://www.uksmg.org/content/ic706_fix.htm. Mine had this problem 7 or 8 years ago and just turning it back and forth then adjusting it with a volt meter into a dummy load fixed it.
    73 Steve KB3UWC
     
  5. KC8QVO

    KC8QVO Ham Member QRZ Page

    You are a smarter op than I was already. My first HF radio was an IC-718 (still have it, been running FT8 with it - still a great HF-only rig). That was back at the end of 2000. My thought was HF is where I wanted to be so that's what I started with. The licensing came later. It wasn't until 2002 when I got my General that I could use the radio, though. After I got my tech in the spring of 2001 I got a HT to get on the air. I had the choice of the 706mkIIg - but it was considerably more expensive. Looking back on it, that would have still been the way to go. That isn't saying the 718 is a bad radio, its just so much more limited without 6m, 2m, and 70cm, plus no FM (could do 10m FM if it had it).

    From a versatility standpoint - the 706 is a good radio. You don't give any letters after the 706, so I am assuming it is an "original" 706 that does HF, 6m, and 2m, I believe with reduced power (20 watts maybe?) on 2m, with no 70cm. That is still a capable radio, but it is certainly aging. The 706 series was already well in to the mkIIg in 2000-2001 when I was getting in to the hobby so it is likely over 20 years old.

    Lots of unknowns. You're a new op, obviously, and none of us on the forum know your background with radios up to this point so I don't think it is fair for anyone to interpret "what may be wrong", specifically, with the radio without some known check points.

    I would second the dummy load idea. If you are in to building stuff - you can make one out of resistors. The catch here is to get the resistance that the radio sees (in this case - pure resistance - there is complex impedance to deal with - bringing in inductance and capacitance - but that is another subject for another time) to be 50 ohms. That can be with any value resistors as long as the combination (using series and parallel circuit rules of Ohms Law) brings you to 50 ohms. For example - if you use 20 watt 200 ohm resistors it would take 4 in parallel (200/4 = 50) to get you 80 watts at 50 ohms.

    Here is an example of a stripline resistor - it is intended to be bolted to a heat sink. This one is 50 ohms/100 watts:
    https://www.ebay.com/itm/100W-50ohm...543779?hash=item5b571d05e3:g:q-kAAOSw7z1aEpCu

    You could use 4 of those - 2 in series and the 2 series sets run in parallel - to get you back to 50 ohms at 400 watts - and they are only a couple bucks a piece. This is way over-kill for your purpose, but it is an example of the construction style you can do with the stripline resistors. How about 12kw continuous with water cooling?
    https://www.ebay.com/itm/12kW-Flori...654067?hash=item48a974def3:g:qOYAAOSwIClanKGO


    Not that I don't think that would be the issue, but that might be way too deep of information in the early stages of trying to define the problem.

    So we have a more clear picture of what may be going on:

    Plug an antenna (since you likely don't have a dummy load at this point) in to the VHF antenna connector. Set the radio to 146.550 (or close - somewhat in the middle of the 2m band but not the FM calling frequency). Set the mode to USB (not FM). Set the power level to the lowest available. Press the PTT button on the mic. Don't talk, just press the button.

    Does the TX icon on the display light up?

    If the squelch knob is set to where you can hear white noise you should see an "RX" icon on the display. Turn the squelch up until the white noise stops. The "RX" icon should go out. Open the squelch again by decreasing the knob setting until you hear white noise. The "RX" icon should come back on. That is what you should see with the "TX" icon above as you press the PTT button and let go. With the "RX" icon on (squelch open) you should see the display toggle between the "TX" with ptt pressed and "RX" with ptt released.

    Is this happening?

    If it is not it might be a pretty easy fix. It would require tracing the mic circuitry back to the radio (test the mic PTT off the radio first, then go to the radio side of it - there could be a fuse blown, broken wire, broken pin, etc).

    If the TX icon is toggling correctly - then we need to move to more troubleshooting. If you have another radio that can receive (scanner, handheld, etc) that would be great. If not, if you can get in touch with someone locally that can help you that will be best - and maybe they have a dummy load you can use also.
     
  6. W9WQA

    W9WQA Ham Member QRZ Page

    yeah, does ANYTHING happen when you key the mic?
     
  7. WR2E

    WR2E Ham Member QRZ Page

    Looks like a 'hit and run'. OP hasn't been back since he posted his question.
     
  8. NN6D

    NN6D Ham Member QRZ Page

    had a same problem with mk2
    indeed it was the trimmer cap
    I ordered 2 trimmer caps from rf parts and put new one on there
    was a bitch to adjust and it seems it has also failed
    it is possible to adjust it for the radio to work but not for the voltage described in service manual
    so now the question is do I put on the second trimmer cap and hope it works for more than five minutes or find a different trimmer cap?
    it is absolutely hard-squared to solder this part onto the board without hot air gun and paste because of proximity of other parts so i even ordered extra small tips for my hakko solder station just for this from ali express...
    they'll be here in about a month, together with several other trimmers for pennies from PRC. maybe one will work...
     
  9. KM6QPL

    KM6QPL Ham Member QRZ Page

    Yeah sorry guys some things came up in life. however I believe I may have fixed it no way of knowing right now with the HF side of transmitting I tweaked with a screw labeled c267 or c627 can't exactly remember. If I can find the forum where I found it then I will link it. However thanks for all your help I was watching and did try the suggestions as you listed them. Once again I apologize when those personal issues arose.
     
  10. KC8QVO

    KC8QVO Ham Member QRZ Page

    Thanks for the post back. As to issues coming up - I think most, if not all, of us can relate. No worries there.

    As to the cap you tweaked - that scares me that you're doing that.

    Many a good radio have met the fate of the "golden screwdriver", otherwise affectionately known as "tweakin' and peakin'".

    Unless you have proper tools to align the rig and the service manual describing the process I would keep your hands out of those adjustments. Nothing good is going to happen getting in there, otherwise.

    That having been said - if you have access to proper tools (oscilloscope, DVM, calibrated signal generator [RF], preferably a spectrum analyzer/service monitor that can read power and display transmitted RF spectrum) and you can find the service manual for the rig describing the alignment processes - it can be a great learning experience.

    I remember trying to align my TS-2000 years ago before getting my service monitor. I used another HF rig as a signal generator to set different levels by tuning the VFO in or out to get the received signal on the TS-2000 to change to where it needed to be. On that radio there is a service menu that allows you to do a lot of the alignment in the rig. However, it is done at set frequencies where you don't have the ability to change a value - all you can do is "save" the value. So you have to give the rig the input it needs then use that as a set point. Its a real PITA.

    When you get in to the RF and DC level adjustments (reference oscillator, filter tunings, control voltages, etc - the adjustments made with internal trimmer pots, caps, and inductors) you have to get those in spec for the radio to work properly. Your VFO frequency readout vs actual frequency, harmonic suppression, and transmitter driver + final drive and modulation levels depend on it.

    Again, there is way too much to screw up under the hood if you aren't aware of what you're doing.
     

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