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Author Topic: Cleaning roller inductor  (Read 350 times)
KW4GT
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Posts: 135




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« on: December 07, 2018, 09:44:08 AM »

I just got an MFJ-989D tuner at a great price off ebay that was supposedly never placed in service (yeah, and I'll gladly sell you some oceanfront property in Arizona).  There's a bad spot on the roller inductor that just happens to be almost exactly where I need to use it at for 17 meters.  So far I haven't found any other bad spots, just that one.

When I get a chance to work on it what's a good method of cleaning the inductor?  Shine it up with some 4000 grit sandpaper, or is that too aggressive?

thanks in advance.
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“Anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge.'” ― Isaac Asimov
KX4OM
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Posts: 310




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« Reply #1 on: December 07, 2018, 10:17:57 AM »

I'm looking at the photo on the MFJ site, and the 989 looks to have the same type of roller as the 969, which I have. The roller is inside of the coil, if so. A problem I had was intermittent operation. It turned out to be gunk accumulating where through roller rod contacts the copper or phosphor bronze tab. I cleaned that, and no problems since. I see it as a routine maintenance  task.

It may be possible to insert a string with a polishing compound like Brasso on it between the affected turns. I would try it without the compound first.

Ted, KX4OM
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WB6BYU
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Posts: 17920




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« Reply #2 on: December 07, 2018, 07:30:09 PM »

If the coil is silver plated, use a silverware cleaner rather than sandpaper, as the
plating is quite thin and you'll quickly grind it off.  If it is accumulated gunk,
then try wiping it off, possibly with some alcohol on a swab.

On the other hand, if there is a rough spot there the coil has arced, you may need
to be much more aggressive to smooth it down, but at that point you probably
have already lost any plating at that point.

Even if it isn't silver plated, the same principles apply. Any physical abrasion or
grinding may make it more likely to accumulate crud in the future.
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G4AON
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Posts: 1221




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« Reply #3 on: December 08, 2018, 05:05:28 AM »

Don’t use Brasso! It is very harsh, it will remove any plating making the problem 10x worse in the future. Also it leaves a residue to minimise tarnishing.

I would try ordinary isopropyl alcohol, or “non lubricant” switch cleaner (the stuff that evaporates leaving no trace).

73 Dave
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N1CX
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Posts: 115




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« Reply #4 on: December 08, 2018, 06:03:50 AM »

Ketchup and a toothbrush.
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KD6RF
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Posts: 756


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« Reply #5 on: December 08, 2018, 08:06:12 AM »

If it is silver plated, and you want to get rid of oxidation, look up coin cleaning.  Skip the ones that show abrasive cleaning, and find the "electrochemical reduction" method using baking soda and aluminum foil and hot water.   Some recipes use salt as well, but it doesn't seem to make much difference.

I *believe* that it does not remove any silver... and it does leave the material oxidation-free.  It worked nicely on some old silver coins I had laying around.
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VTenn Antennas
Bay Area Technical Equip Rental and Test Range
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KW4GT
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Posts: 135




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« Reply #6 on: December 08, 2018, 02:35:42 PM »

OK, problem solved.  Turns out I jumped the gun ASSUMING that there was a bad spot on the roller inductor.  Well, in a way there was, but not how I'd imagined it. 

As the roller began the very last turn it was making contact with the lead coming off the inductor.  Some very gentle bending and persuading moved it far enough out of the way to solve the problem.  (And everything under the hood was absolutely pristine, so now I actually do believe this unit was unused).
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“Anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge.'” ― Isaac Asimov
KO4NR
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Posts: 172




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« Reply #7 on: December 11, 2018, 05:58:50 PM »

Treat it with DEOXIT now and again to prevent corrosion.
Worth every penny!!
https://caig.com/product/deoxit-d5s-6/
73,
Bill KO4NR
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N4MQ
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Posts: 289




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« Reply #8 on: December 11, 2018, 07:48:39 PM »

I have used mothers wheel polish and it brightened the windings nicely with a q tip and then a wash with water and air dry.  You dont want to remove material but trash.  Black silver oxide is conductive and not a problem.  Cleaning the shaft  and roller wheel is a bulk of the resistance you may encounter.  Oil the shaft too.  Woody
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N4MQ
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Posts: 289




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« Reply #9 on: Yesterday at 04:34:23 AM »

OBTW  MOTHERS wheel polish is my go to polish for metals and all plastic and bakelite knobs on old radios.  Its a very mild polish that is very useful from wheels to headlight restorations.  FYI Woody
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