sorry for the abrupt QRT today on Ramsauer Größtenberg. I was just in the middle of the pile-up on 20m when my IC-703 started making problems, reducing power on it’s own and in the end completely stopped putting HF out.
Not sure what the problem is, but after switching it off for a few minutes the rig worked again … but just for a short time, then the same thing occured again. I heard G6TUH calling me several times, but was not able to answer. Sorry Mike!
Although I could not complete the QSO’s and was not able to wish all the Chasers a Merry Christmas personally I enjoyed a very sunny and warm day on the summit.
I wish you all a Merry Christmas and a Happy New Year 2016!
It sounds like a temperature related problem.
Our rigs usually are built inside a black metal case, which can get really hot when placed under the sunshine.
Also, if I recall correctly the IC-703 puts 10 w out, which means more heat being produced by the final transistors.
It’s highly recommendable that our rigs always work in the shade and as ventilated as possible.
Best 73 de Guru
That’s not the problem, Ed.
Martin wrote he was receiving stations calling him but output power was reducing down to zero TX, but RX was still working, which means that the rig was ON, so connection to battery was OK.
My IC703 stopped transmitting due to a failure of the predriver device, which in some rigs was biased too far on at the factory. This problem is well known and there is an article on it at mods.dk.
The device itself is quite cheap but a nuisance having it fail on a summit. Hope yours is a simple fix. IC703 is a very nice portable radio, mine has a FL53A filter making it excellent for CW.
in the cases I have read about, the device fails completely due to excessive heat, so your intermittent transmitting may not be due to the same cause. The device is a 3 or 4 terminal chip looking like a MMIC or an old style dual gate mosfet.
Good luck and I hope you get your ic703 going again. Mine has not missed a beat since the repair was done.
My IC-703 is one of the very early ones, without the 6m option. They had a catastrophic fail in the PA driver design, where the driver Q150 was biased directly from 13.8V. Icom suggested a mod where you insert a resistor, reducing the supply to a more humane level of 8V.
Once I replaced Q150 and did this mod, everything was fine, and has been ever since.
I don’t know if your 703 is a s old as mine, but if so, I wrote an article in the Danish magazine ‘OZ’ explaining the repair (also describes how to fix the CW key input, so it’s less sensitive to RF leakage).
Thanks for that link and the article. My 703 is without 6m though the traces are on the board, just the components missing and the firmware omits 6m from the band options, sadly. During the 6m challenge I often wished for 6m in this radio.
The key line is sensitive to local RF and I will try your fix for that.
I started out with the external wire (Fig. 1), then soldered a gnd wire instead, as shown in Fig. 2.
A couple months after, while installing the CW filter (thus having everything taken apart anyway), I did as shown in Fig. 3. Everything has been just fine since.