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How to clean pots? AR3 Newbie seeking info


Guest biminyrd

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Guest biminyrd

Ok, I'm new to repairing speakers, though I've had my AR3's for 15years since my father gave them to me.

I am only getting sound from both the woofers, and nothing from the tweeters or mids.

I've searched the forums.

I've figured out I should try to clean my pots, but I can't find a post that will tell me how. How do I remove them, what do I clean, with what can I clean them (sand paper/emery paper, wd-40, some other special electrical cleaner?), etc?

is there a faq or sticky post that i'm missing in my search?

I've found the diagrams for bypassing them, but I don't really want to do that 1st, plus I've seen posts that are not very clear that this is the proper solution.

thanks in advance.

aaron

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>Ok, I'm new to repairing speakers, though I've had my AR3's

>for 15years since my father gave them to me.

>I am only getting sound from both the woofers, and nothing

>from the tweeters or mids.

>I've searched the forums.

>I've figured out I should try to clean my pots, but I can't

>find a post that will tell me how. How do I remove them, what

>do I clean, with what can I clean them (sand paper/emery

>paper, wd-40, some other special electrical cleaner?), etc?

>is there a faq or sticky post that i'm missing in my search?

>

>I've found the diagrams for bypassing them, but I don't really

>want to do that 1st, plus I've seen posts that are not very

>clear that this is the proper solution.

>

>thanks in advance.

>aaron

The good news is that it's do-able. The bad news is that it's a pain in the neck. You have to remove them and take them apart. This is done by gently prying open the hinged spring clip which holds them together once you get them out of the cabinet. On the advice of others on another message board, I tried Caig's De-Oxit and found it to be worthless. Lucky boy that I am, I still have freon and found that useful, helps contribute to destroying the ozone layer of the atmosphere too. I used that in combination with an emery board, sandpaper, and some other brand of electronics part cleaner on 4 AR2a pots. It wasn't a perfect result but it was much much better. I also have a pair of AR2axs to restore and that will have the same problem. I have an inexpensive Dremmel like high speed rotary tool kit I bought at Costco for cheap a few months ago and I will try that with the wire brush attachment...carefully and gently. Be sure to clean all of the conductive parts, the brass race at the endpoints, the surface of the coiled wire and the copper contactor on the rotary slider (I forgot that part first try and it was green with corrosion and didn't work when I first put it back together.)

If it hasn't been done already, you will want to replace all of the capacitors too. When completely defective (all of the ones in the AR speakers I acquired were) they will prevent the midrange and tweeter from functioning but even if they are just out of spec and that always happens with time, they increase the risk of damage to the midrange and tweeter drivers. I'm not going to get into a war here but IMO the inexpensive electrolytics are good enough for me (under $1 each.) If you do decide to spring for more expensive ones like polypropylenes, the series caps are supposedly much more critical than the shunt caps. Some people with extreme views say that for best results, you should wire a very low value polypro cap such as 0.25 or a 0.5 mfd cap in parallel with each of the others suggesting they beleive the larger value caps are non linear around the zero volts crossing point. One contributor here I often disagree with claims that in a blind test and against his own preconceived expectations, nobody could hear the difference between the polys and the ordinary cheap electrolytics and this is one instance I choose to take his word for it.

I do not recomend and I think most (but not all) here would agree that it is not wise to jump out the potentiometers. Not only will you lose their functionality but that will not yield the flattest frequency response, the one indicated by the red dots on the back and recommended by the manufacturer.

Good luck.

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Aaron,

Here are some photos to go along with Soundminded's comments.

They show a partly refurbished control that is in decent shape. In this case the corrosion did not cause significant pits on the disk inside the resistor coil, or a hole in the wiper tip, both of which are common problems requiring replacement parts.

Roy

post-101150-1182743551.jpg

post-3-1182743551.jpg

post-3-1182743552.jpg

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Aaron

There is lots written on this subject.

You asked how to remove the pots. You have to remove the woofer and work from inside the cabinet. As was mentioned you may as well replace the caps while you are at it. Be sure to retain the fiberglass stuffing and replace it (the exact amount) when you are ready to put it all back together. You will probably need new caulking for the woofer. Mortite rope caulk works, as does the black brick of goo sold in the electrical supply section of a hardware store.

The pots are held in by nuts, removable from the outside but then you pull the pot itself out through the woofer opening. I'm sure there are photos and schematics posted here somewhere.

I found that a small brass wire wheel chucked in a Dremel, along with contact cleaner, worked well for cleaning things up. Clean the brass contacts, the coil springy thing, the thin brass wiper. When finished you should check the pot with a meter to make sure you are getting a smooth increase from 1 to 15 ohms (I think those are the values) as you rotate the center shaft. If not, take it apart again and clean it some more. A LIGHT coating of dielectric grease may help preserve your shiney metal.

good luck

Kent

PS sometimes the pots are beyond repair. I bought a pair of speakers with the red plastic shafts and they were totally melted!

PPS Check the Library for schematic and Instructions on Repairing AR 3/3a crossover:

http://www.classicspeakerpages.net/ar/classic/ar-3/ar3.htm

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