IC 706 MkII-G problem

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Shane
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IC 706 MkII-G problem

Post by Shane » Fri Apr 14, 2017 9:34 pm

So let's turn that other discussion on its head and discuss ham radio on a broadcast board (not a new idea--obviously the board operators thought to include ham radio as a forum)!

IC 706 MkII-G produces no output on 2 meters. It used to. Now it acts like there's high SWR (there isn't) comes on with some decent power a quickly - less than a second - folds back to nothing.

I'm probably going to wind up sending it to a shop equipped to handle such things but before I do I thought I'd check here for any advice.

In monkeying around with it the first or 2nd time it did this I switched to AM to see what that would produce. I got some carrier but it was off frequency. I first thought slope detection but this was the opposite way around: trying to hear AM on an FM receiver rather than FM on an AM receiver, which is done by slope detection.

So I'm still buffaloed by this one. I have not checked to see whether I can get any output on lower bands but since those freqs exit the rig from a different connector I didn't think that would matter.

BTW, is it just me or does NBFM as we use on the ham bands sound much nicer and less distorted on an AM receiver? So long, of course, that you tune off freq.

This is perhaps an outgrowth of the fact that when I got my ticket, AM was dominant on 6&2. I got used to the background noise going DOWN when the operator keyed up, and UP when the operator keyed down! FM, especially with an open squelch, still sounds backwards to me.

I also have an uneasy truce with squelches so I'm doubly biased. <drift mode off>

Any ideas on the '706?
Mike Shane, CBRE
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jammerdave
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Re: IC 706 MkII-G problem

Post by jammerdave » Sat Apr 15, 2017 9:10 am

Hmm... I'd take a look at the PIN diode T/R switching for the 2M section.

df

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RGORJANCE
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Re: IC 706 MkII-G problem

Post by RGORJANCE » Sat Apr 15, 2017 11:06 am

Good idea on the pin diode.

I have a 706 too and I seem to remember losing the output device/brick on it. Additionally, I also got an ICOM FM only rig (I think it's an IC1200) that keeps tossing out pa modules every couple years. Symptoms are the same on the 2M only rig.

Fossil

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Shane
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Re: IC 706 MkII-G problem

Post by Shane » Sat Apr 15, 2017 10:14 pm

Now that's a couple things that I have not heard yet. Guessing the PA modules are separate for <54 MHz. Either way, it's looking like a trip to SD for the old girl.

I contacted the fellow who took over Burghardt's repair service. Reviews are kinda mixed but lean toward good.

Thanks for the clues.
Mike Shane, CBRE
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kcbooboo
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Re: IC 706 MkII-G problem

Post by kcbooboo » Sun Apr 16, 2017 6:37 am

The service manual IS available on-line. I took a look at it and it appears they don't use RF brick PAs but discrete FETs. Possibly relays to switch the bands.

Bob M.

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