[Lowfer] Icom R75 Frequency Jumps

[John Andrews]

Todd,

Hmmm...top cover off, bottom cover off, remove the 4 screws holding the 
front panel to the chassis, unplug the ribbon cables to the front panel, 
remove the panel, remove the 5 screws on the shield to the front panel, 
unplug the headphone jack cable, remove the shield, remove the PBT and 
AFG/RFG knobs, remove the nuts on the pots, unplug the board the pots 
are mounted on, and remove the board. Now you can change the pots, and 
undo the above!

The pots are pretty well sealed - doubt you could clean them without 
removing them and drilling holes. My morning project at work today is to 
clean up the mess left by a customer that sprayed silicone contact 
cleaner into one of our products, trying to hit the sealed pots. Not to 
compare the Deoxit with the cleaner my customer used, though.

Yes, ventilating the R75 is a good idea, although that may make it less 
usable for the microHz stability some of us need for LF work.

As Jay found with GPS locking, there are 4 DDS circuits, and all have 
integer round-offs that will still leave some little frequency offsets. 
But the external source would pretty much eliminate warm-up frequency 
shifts, and allow the R75 to be turned on/off and still do the high 
precision stuff.

JA

On 8/7/2013 10:41 PM, ToddRoberts2001 at aol.com wrote:
> John thanks for the heads up on the problem with the noisy PBT dual  pot
> control in the Icom  R75. I'm not sure how hard it is to access those
> pots? Do
> you have to pull the front panel off and is it a very involved  procedure?
>
> My thinking is if someone has a currently good working R75 one could
> extend the life of the pots with a good shot of Deoxit F5 fader
> lube into the pots? The Deoxit F5 has restored some pretty noisy pots
> for me in the past. It might be good prevention to put some lubricant
> in those pots if possible. Could someone do it with those pots, or are they
>   sealed?
>
> Another thing I am doing with my R75 is I leave the top cover off all the
> time.
>   I have discovered that leaving the top cover on literally turns the
> chassis of the R75
> into an oven. After being turned on for an hour or so many parts inside
> were
> almost too hot to touch. I am sure this would shorten the life of some
> components like the electrolytic capacitors and possibly others.
>
> I found leaving the top cover off allowed most of the heat to escape
> so most of the components are now cool to the touch and a few
> that were very hot before are now barely lukewarm.
>
> Icom did not provide for any air circulation with the top cover on.
> There are no louvers or vents for the air to circulate. One project I
> am working on is to build a new top cover using perforated metal
> which would look a little better than leaving the top wide open. But it  is
> worth it to have a cool-running R75 and it is used indoors all of the  time
> here anyway so it is not exposed to any outside weather.
>
> Another benefit of having the R75 locked to GPS is the radio doesn't  need
> to be turned on all the time to help stability like with the  internal
> crystal.
> It has instant-on stability with the external GPS standard connected, so it
> is good to go with ARGO right after turning it on and the rest of the time
> it can be left turned off when not in use.
>
> Thanks, 73 - Todd WD4NGG
>
>
>
> In a message dated 8/7/2013 6:58:54 P.M. Eastern Daylight Time,
> w1tag at charter.net writes:
>
> 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
>
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