[Lowfer] Icom R75 Frequency Jumps

[jrusgrove at comcast.net]

JA

Nice find ... know you've been plagued with this for some time now.  After hearing about the problem 
some time back I started shutting mine down when not in regular use. Good to know the fix is 
relatively simple. Thanks for the info!

JR




----- Original Message ----- 
From: "John Andrews" <w1tag at charter.net>
To: "Discussion of the Lowfer (US, European, &amp;UK) and MedFer bands" <lowfer at mailman.qth.net>
Sent: Wednesday, August 07, 2013 7:09 PM
Subject: [Lowfer] Icom R75 Frequency Jumps


>I have two Icom R75 receivers, both more than 10 years old. They have pretty much run 24/7 between 
>here and Maine, a sort of service that they probably weren't designed for. In the last few years, I 
>have replaced most of the electrolytics.
>
> But starting a couple of years ago, I began noticing small frequency jumps on the order of 0.1Hz 
> when looking at QRSS screens. Didn't happen all of the time...one or the other receiver might be 
> OK for weeks. My first approach was to look at regulated voltages, but that got nowhere. The 
> troubleshooting was made more difficult by the slowness of a QRSS30 or 60 screen -- a jump 
> wouldn't be noticed until a minute or so later.
>
> To make the long story short, the culprit turned out to be the passband tuning control on the 
> front panel. That's a dual 10k pot with concentric shafts and a detent in the center of 
> revolution. The pot feeds 0-5V DC signals to A/D inputs on the microcontroller. That detent 
> position had become very noisy, and the controller was programming the DDS circuits accordingly. 
> The pots were made by Toko, and have been discontinued. But Icom seems to have a good supply at 16 
> bucks apiece. Since I had also been having issues with audio volume jumps, I picked up replacement 
> AF/RF gain controls as well.
>
> Anyway, all seems to be well now. The line on an Argo display now looks like the EKG of a patient 
> that assumed room temperature some days ago, a good thing in this case.
>
> John, W1TAG
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