IC 706 MkII-G problem

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Shane
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IC 706 MkII-G problem

Post by Shane »

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?
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Re: IC 706 MkII-G problem

Post by jammerdave »

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

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Re: IC 706 MkII-G problem

Post by RGORJANCE »

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.

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Re: IC 706 MkII-G problem

Post by Shane »

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.
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Re: IC 706 MkII-G problem

Post by kcbooboo »

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.

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Re: IC 706 MkII-G problem

Post by Shane »

This is still an issue as there were a couple of new developments. 1) I found the rig puts out fine in SSB mode but it drifts in freq somewhat, and 2) a different tech told me both symptoms - the drift and the lack of carrier - are likely because of a defective variable cap in the VXO. Have not dove in yet to do anything to it, but I’m thinking it will affect CW operation, too, and that will be enough motivation to fix it. :roll:
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Re: IC 706 MkII-G problem

Post by Shane »

Well, wrong again. CW works fine. So does AM. So only VHF FM has the issue. (And possibly AM on VHF - need to try FM on 29&50 MHz too yet.) Haven’t looked at the service manual for the part that the tech told me about but just been using what works.
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Re: IC 706 MkII-G problem

Post by Shane »

Had time to mess with this this evening. Opened it up and used the service manual to guide me to the aforementioned possibly flaky variable capacitor. Moved it ever so slightly with a small screwdriver, buttoned it back up and tested successfully. So it’s at least temporarily fixed.

Had to re-educate myself in how to use it on FM again. I guess I’ve been working around the problem with other radios for almost 4 years! That’s a long time to get a round tuit but not a record for me.
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