[Lowfer] Icom R75 Frequency Jumps

[Warren K2ORS]

Tnx John, good tips will order spares for my R75s ($16 for a pot, ouch!)

73 Warren

On 8/7/2013 7:09 PM, John Andrews wrote:
> 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
> ______________________________________________________________
> Lowfer mailing list
> Home: http://mailman.qth.net/mailman/listinfo/lowfer
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Lowfer at mailman.qth.net
> Post must be less than 50KB total for message plus attachment!
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>