Cleaning a roller inductor.

[Tractorfan]

Hi,
I think I've posted this in the right place.
I have been given an MFJ aerial tuning unit which includes a large roller inductor.
About a third of the way along its continuity becomes erratic. I tried a squirt of Servisol, but it's made little difference. Before I strip it down and clean the parts separately, is there a recommended way of cleaning it? I don't really want to bung it in the dishwasher if I can avoid it in case the detergent attacks the coil.
Thanks in advance.
Cheers, Pete.

[HamishBoxer]

IPA (isopropyl alcohol) might work.Is it covered in grease or anything I wonder?

[David G4EBT]

Years ago we had a TV with a turret tuner, the many contacts of which regularly tarnished, taking the stations off-tune. I used to use 'Silvo' (or Duraglit') wadding, which worked a treat. I'm my amateur radio days, I built a home-brew ATU using a roller coaster with a silver-plated coil, and that too responded nicely to Silvo when continuity became erratic.

I guess there will be similar products available in France, but this is the stuff I'm referring to:

http://www.pentonshardware.co.uk/pro...at_id=2&id=157

Hope that helps a bit.

[Radio Wrangler]

On a roller, it's probably surface burning through the plating on the wire, and not cleanable. Nature's way of telling people not to turn them with the key down.

If it doesn't polish out, you'll need to rewind it with new wire. I've heard of people 'turning the wire round' by rewinding the original back on.

DAvid

[G6Tanuki]

I'd try wiping the coil and the roller-wheel and the spindle-it-runs-on with IPA as a start: you want to get the moving parts grease-free (and dust-free too).

Good roller-coasters will have a silver-plated coil: this can tarnish and develop a black coating. Silverware-cleaner followed by swabbing with IPA being needed here, but go carefully and remember the silver is only a plating: don't clean too vigorously or there may be no silver left!

[I never really liked the 'classic' roller-coaster with all its moving contacts: the best variable inductor I ever came across was used in the RACAL Syncal-30/TRA931 transceiver - it used Gold-plated flexible wire that was wound and unwound from a helically-grooved, insulated drum on to a similarly-grooved but conductive drum that sat alongside it]

[Andrew2]

I've recently given up trying to sort out the small roller coaster which lives at the base of my Topband vertical. For ages it has been giving me terrible intermittent SWR's and after the usual attacks with Servisol etc I gave it a careful seeing-to with one of those fibre pen thingies. No improvement. So I've whipped it out and chucked it in the cupboard and gone back to my tapped-coil-with-croc-clips method and all my probs have gone away.
To be fair to the poor old thing, it was very worn and the copper was showing through over lots of the winding.

[emeritus]

When I used to do my own black and white photographic processing, I found that exhausted fixer was effective in silver-plating copper and brass. You just had to clean the metal and dip it in the liquid, or swab the area to be plated with a cotton wool pad soaked in the liquid. If you do know anyone who still does this, you could ask for some of their old fixer.

[trh01uk]

Put it in the dishwasher, if you have one. If you have a wife too - you might want to OK it with her first!

Richard

[Bazz4CQJ]

What can you see when you look at it Pete?

IPA is really a poor solvent; if there's serious (organic) dirt there, a drop of acetone on a Q-tip will do much better.

I wonder whether the MFJ tuners (I have one too) run to the expense of silver plating? Could it be nickel? Either way, I am definately not one of the "dishwasher" brigrade, except perhaps for bits of lawn mowers.

B

[russell_w_b]

You need to check the springs that hold the grooved wheel against the wire on the coil, and ensure that the hole in the wheel hasn't become too worn and is turning as the coil turns. And that it rides evenly and freely all the way along the coil.

Clean the shaft the wheel rides along with IPA. If it's tarnished, Goddard's 'Silver Dip' will clean it first. If you use Brasso wadding, don't wear the plate off it - it's abrasive. If it's a porcelain coil former, remove it if you can and put it in the dishwasher. It'll be fine.

We used to use Colclene 2000 if we'd to address a dodgy roller-coaster, sprayed on a rag wrapped round the coil and pulled backward and forward. It usually got us to the end of a transmission until we could swap it out.

[Tractorfan]

Hi,
Thanks for all your replies.
I took the inductor apart yesterday and there was plenty of grease on the moving parts. This was cleaned off with meths and I also wiped the inside of the coil with it too.
I put a tiny smear of conducting grease (used on contacts of industrial switch gear), then reassembled the inductor.
I'm pleased to report that it now works much better!
Incidentally, my unit has a coil that remains stationary while a brass wheel travels around the inside. I think that there are other types where the wheel stays put as the coil turns. Is this correct, or is my brain playing up again?
Thanks again.
Cheers, Pete.

[m0cemdave]

Yes, that is correct, and the type with the rotating coil is much more common.

As mentioned above, the best ones are those with a tape or wire that is wound from one (insulating) drum to another (conducting). But they take up twice as much space.

[Andrew B]

If it all comes apart easily then re electroplating it with silver is quite an easy job once you have everything clean. I remember doing it at school with silver nitrate onto copper wire, we even made mercury silver amalgum by stirring a blob of mercury in a silver nitrate solution and watching the crystals grow.

A note, meths is a better solvent than IPA for most uses, it has a bit of methanol in it (called a 'searching solvent'). And you can get it form your local DIY shop. It is not as pure as IPA and for critical items a water/surfactant (soap) wash may be needed afterwards.

[FrankB]

I have had good luck putting the coils into an ultrasonic cleaner, then fully drying them in the oven at low heat. A drip of light oil or automatic transmission fluid into any bearings is needed.

The ultrasonic cleaner works great for tuning capacitors also, but remove the mica trimmer sheets, the same for compression trimmers on IF cans too.
Here I use Dawn (TM) brand liquid dish soap. If you get one from Harbor Freight Tools, DO NOT use their cleaner in it for any aluminium item. It will attack it. Dawn soap works great. Rinse thoroughly when done and dry in the oven at low heat for a few hrs.

For missing silver plate, I used to use an electroplating pen for jewelry & silver plate.
They came with silver, gold and copper solutions.

The ultrasonic cleaner works well on R/P switches in tape decks and rotary deck switches too. Just remember to lube, or they can seize up. Got that Tee shirt.