Re: [IC-7000] Re: Oscillation


James Brock <jamesbrock@...>
 

Steve, thank you for taking the time to give me some suggestions regarding the repair of my IC-7000.  I have put on a 50 ohm load on the antenna input/output connector.  It didn't seem to make any difference.  

I copied and saved your full description so I will not overlook any of your suggestions. 

I am inclined to think the problem is within the unit.  When I can see the carrier swooshing through on the JT65 screen I see the carrier change directions.  It always start on the right side, the high frequency side. Then it slowly sweeps through to the low side, to the  left. I can hold my had over the cabinet fan on the top and the frequency will swoosh the other direction, to the right.  It is something that is heat sensitive.

I am inclined to think it is a grounding problem somewhere inside. 

Now about the heat sensitivity, could also be a slight change in voltage out of a series regulator. 

I am not giving up.  Most of my experience with electronics that last twenty-three years has been with TV UHF transmitters and translators.  I know a person can certainly get fooled.

Wishing you the very best and again thank you.
 
James Brock 541-868-5827


On Tuesday, December 29, 2015 5:58 AM, "w3ahl@... [ic7000]" wrote:


 
While it sounds like the spurious signal is originating inside the radio, based upon your description, I would suggest eliminating external sources first, since that is much simpler to do.  

Disconnect all cables that you can from the radio (mic, antenna, tuners, CI-V, external speaker, etc.)  If you can hear the signal in the speaker without the computer connected, disconnect the computer.

If possible, power the radio with a battery.  

Turn off the computer (if possible) and most important -- turn off all network routers and switches in the entire house.  The signal you describe sounds like what I've seen as RFI from LAN cables (especially 100 Mbps).

And finally, turn off power to the entire house.  If the computer must remain on to see the problem, disconnect it from any UPS unit and unplug the UPS.  I notice from Google Earth that there is an overhead power line at the back edge of your property.  Any problems with RFI from that?

If the above doesn't eliminate the birdie, then it probably is indeed inside the radio.  What is the serial # and year purchased (if original owner).  What frequencies have you seen the problem on?

There are several potential grounding issues inside the 7K.  Various changes to grounding springs, PCB artwork, circuit design, etc. have been made over the years, especially in radios made prior to late 2010.

Has the radio ever been returned to an Icom Service Center for repairs?  Did they make any updates while it was there?  There were some ground springs added to the PA board and also to the DDS board and one of the cables from the DDS to the Main board.  In this Group's Files area, look the "7K GROUNDING FINGERS.doc" from by me (s_ahlbom).  That shows what I believe to be the correct configuration.  Remove the covers and verify they are installed and bent up enough to contact the covers.  Also verify the pink pads are installed as shown.  They provide some thermal conductivity, but are also RF absorbers to attenuate noise.

Older radios also tend to have poor grounding from circuit boards to the cast aluminum due to surface oxidation of the aluminum.  This is especially a problem for some grounding springs/clips along the front edge of the Main board to the front of the chassis. The solution is to use 320 grit emery paper to remove the oxide from the aluminum, then scrub in Noalox to prevent it from reforming (as done to aluminum tubing on Yagis or aluminum wiring).

Another problem is with the metal fabric grounding pads used to ground the front of the Main board to the top cover.  Over time, heat causes the black foam inside the metal fabric to deteriorate, resulting in poor contact to the top cover.  If you squeeze the pad, it won't spring back well and black rubber particles will fall out when it is moved.

And finally, the small coax cables connecting the DDS to Main board and the Main board to the PA board can build up a rather hard crust of black tarnish on the silver plating of the connector, that can cause poor RF grounding of the shield.  The problem appears to be inside the outer shield of the connector where it is crimped onto the copper coax braid.  The only reliable fix for this is to replace the cable.  They are only a few dollars from Icom Parts in WA.

Steve, W3AHL

---In ic7000@..., wrote :

 This is somewhat hard to explain.  But rather frequently now I get an oscillation showing up on my JT65 screen.  You can see it slowly sweep across the screen from right to left.  Strange thing I hold my hand over the case blower it stops and goes the other direction. No doubt somewhat heat related. 

If I have the input on the antenna that has not yet been tuned (remotely) to frequency the oscillation is worse.  Put on the carrier to get the antenna tuner on frequently and the oscillation considerably lower in intensity, sometimes goes off.

When it gets so bad nothing works I recycle it by turning input DC power on and off. 

It is considerably worse when I have the preamplifier off. 

Recapping, to get it to quit or so low I can operate I make sure the antenna is tuned to frequency. I turn on the preamplifier. And when that doesn't work, turn the power switch off and on. 

It has been going like this for several months. I talked to ICOM about it and they said to reset it. That didn't do any good at all.  The tech at ICOM acted as if something like this could not happen.

Anyone out there have a parasitic oscillation running around? 

I am rather inclined to think it is in the RF amplifier stage.

HELP 

W7DAU
James Brock 541-868-5827


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