HFU HF Underground
Technical Topics => Equipment => Topic started by: ChrisSmolinski on August 04, 2017, 2036 UTC
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I recently dug my Icom IC-735 out of storage. I remembered the last time I used it, the tuning knob was flaky. Well, this time it wasn't flaky anymore, it was dead. After some troubleshooting, I determined that one of the phototransistors on the rotary encoder was dead. It's a Sharp IS-433, which has been obsolete for some time. The replacement Sharp IS-486 is also obsolete, apparently. But some searching around on good old eBay turned up a Chinese (of course) seller with some IS-486s. I got 5 for $6 shipped. They arrived just 11 days later. I just swapped out the component, and the substitute works great. Plus now I have 4 more left over for when the other one dies ;D
I believe this part is used on several other Icom rigs as well, so something to keep in mind if you have one that uses it as well.
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Well, good to know, as the main tuning knob on my bro-in-law's IC-735 has a flaky dead spot on it as well. It's been that way for years, but hasn't died, yet. Right now, I just use that rig to listen to my AM Carrier-Current station AM610 with a 2" wire on the SO-239 connector. Surprised on how well that transceiver sounds on AM RX with a decent speaker behind it. Score one for Icom there.
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The encoder can also have an alignment issue between the LEDs/phototransistors and the wheel with cutouts that spins between them. It is fairly easy to remove the encoder and adjust them, if this is the problem.
Yeah, the 735 is a nice little compact rig! I got mine used from someone that used it mobile in Germany.
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They also suffer from the dread Murata plastic vco/bfo cap issue where they start to degrade causing all sorts of broadband noise. Next time you're deep in the guts of a 735 you might just swap out the plastics with some ceramics.
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Yes they do, along with the R71A. I bought the replacement caps years ago, but it is a PITA to remove the RF shield to swap them out. And I have no idea where the replacements went ;D
So what I do is every so often rotate the trimmer caps back and forth a few times, which wipes of the crud, and the VCO behaves again, at least for another year or two.