I have that problem currently with my HF transceiver: no power output at all in SSB and CW, no matter which band / Frequency, but everything is ok in AM, FM and RTTY... There is also a big difference in current consumptions on TX: only about 4A in (not working) SSB and CW, about 20A in (working) AM, FM and RTTY... Where should I look for the failure?


closed as too broad by Phil Frost - W8II, Ron J. KD2EQS, Kevin Reid AG6YO, PearsonArtPhoto May 1 '14 at 18:52

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  • $\begingroup$ Sounds like you aren't modulating. That'd give you zero power output in SSB, and only bias current draw during TX. CW is a bit weird, though. What model transceiver are you using, and does the modulation meter indicate that you are modulating? No inadvertant setting the mic gain to zero or something like that? $\endgroup$ – a CVn Mar 28 '14 at 13:14
  • 1
    $\begingroup$ Electronic.SE has a close reason: "Questions on the repair of consumer electronics, appliances, or other devices must involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being repaired." I'd argue that applies here, too. A broken radio denotes no RF output, and if you don't know where to look, no answer is going to get you there, especially since you haven't given us a schematic, service manual, or even the model of radio you have. $\endgroup$ – Phil Frost - W8II Mar 28 '14 at 14:21

Ok, sorry for the lack of information (I'm the one who asked the question, but now I've signed up and I'm logged in). My TRX is Icom IC-751 (not the "A" version). The SWR/ALC/Power... meter indicates zero ("0") as soon as I push the PTT in SSB or CW. The mic gain is set to max., the RF out is set at least on 10W everytime. What I've done until now: I've checked and new aligned the PLL, checked some voltages according to the service manual (widely available in internet) on the PLL board, logic board and a few on the main board. Everything seems to be ok, the RX is also very good on all bands, in all modes. I'm not really sure if I really have to measure all the check points from the service manual, or I should limit the troubleshooting to the main board and (maybe) the RF board and that's why I have asked for some tips. I'm not sure if I'm allowed to attach the pdf file of the service manual for the IC-751 here but, as we know, it is easy to find it on the net.


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