Several series of speakers produced by Infinity in the 1970s through mid-1980s contained in most models one or more 5Ω 25 watt potentiometer to control the midrange levels and sometimes those for the midbass and treble. The problem is that the Pollak brand potentiometers used are extremely susceptible to various environmental contaminants both external and internal to the cabinet. This makes for most units found in the aforementioned Infinity speakers to be corroded such that either performance is spotty due to high resistance patches or continuity has been lost. The general assumption here is that the pots are shot and need to be replaced, as many posts elsewhere regarding these speakers stand -*test*-('")ament to. Unfortunately, new direct replacements are exceedingly difficult to source leaving many with non-functional speakers, others to bypass the levels and live with the resultant overly bright and forward sound, or spray lots of Caig's DeoxIt into the pots in an unsuccessful to correct the problem.

There is a simple, but typically overlooked solution of manually cleaning the potentiometer. I've decided to go ahead and briefly write up the basics and provide pictures for those who'd like just a little more knowledge as to how to do this.

First off, carefully remove the woofer and fill material (fibreglass batting in older models and polyfill in later) over the crossover. Locate the larger potentiometer(s) that are the problem (identical to that shown in the attached picture) and note which wires are soldered to which of the three terminals (the two outer pins should measure 5Ω between them with the variable resistance being between the central pin and either of the outer pins inversely). Then unsolder the wires, or cut near the pins for ease if there's sufficient slack to allow soldering later, and remove the potentiometer.

You should have something that looks like this example. Often times the entire upper casing is rusted and large turquoise corrosion crystals will be falling out from the inside. This is typical of these and the one pictured is in better condition than most.

- JP

Fortunately, opening up this particular style of potentiometer is a fairly simple matter and was, in fact, designed to be accessed for maintenance such as this. Take the pulled potentiometer(s) to your workbench or table covered with a newspaper (for the rust) and with a pair of needle-nose pliers or the like, carefully pull one end of the metal loop out of its associated hole. When loose, pull the rest of this piece free and out of its other hole without bending it. This piece is designed to be a bit springy to maintain the necessary pressure to hold the halves together. At this point, the wiper and shaft from the metal half will fall out, but this is no matter. Just make sure you keep track of the pieces.

What'll you now have on hand is the ceramic half containing a central disk and wound wire resistance component, an empty metal shell, the metal hoop that had held them together, the shaft, and the two bent metal pieces that compose the wiper contacts.

- JP

The point of corrosion that causes most of the issues that make the pots non-functional is found at the ceramic half of the housing. In particular, the metal disk at the center is typically badly corroded having turned black and sometimes covered with the turquoise crystals of corrosion from the central brass rivet. Oft times, the wire-wound resistance section is filled with pieces of corrosion from the brass fittings that have either caused high-resistance sections or shorted areas, sometimes both.

- JP

To clean the ceramic half and cure most of the ills, first knock or, preferably, with canned air blow the detritus from the wire-wound section. Then taking a scrap of Crocus Cloth, as found at most decent hardware stores by that name, or a piece of 600 grit sandpaper, scrub the corrosion off the central contact. This may take some effort if it's particularly bad off, but is necessary as not even most chemical contact cleaners can cut through this. What was once black will now be silver and what was green is again brass and you've done your job well. Now, lightly run the crocus cloth across the top of the wire wound section to ensure that it too is cleaned of corrosion and silver again. Do not press hard lest the coils collapse and make the potentiometer unusable.

Then, be sure to clean the corrosion off the wiper half, or at least that portion that contacts the central disk and wires. You can tell which this piece from the backer is as it has the two raised bumps. The crocus cloth works fine here as well.

When done, I prefer to lightly spray both the contacts on the ceramic half and the wiper with Caig ProGold (often packaged with DeoxIT), just to make sure everything will stay relatively corrosion free and working for another twenty years.

If the cosmetics of the rusting metal half bother you, simply take some fine sandpaper and remove the majority of the rust. Then, I prefer to spray it with a shot of Corrosion Block, a product I've found does an excellent job not only stopping rust, but reversing it to a slight degree.

- JP

Now is the time for reassembly. It's mostly just reversing the disassembly process. However, if the wiper* fell out when the pot was first opened, you'll want to make sure it goes back together properly. First, the shaft goes through the hole on the metal half (obvious enough). Then the wiper backer, the bent piece that is identical to the wiper except it is without the contact bumps, fits over the two pegs on the bottom of the shaft. These pegs are differentially sized so there is only one right way. Then align the wiper contact to match the backer, but with the bumps out, and set it into place.

To place the halves together once again, observe the tabs on the metal half. There will be two narrow and one wide. These tabs will align with the notches in the side of the ceramic half, so watch to make sure the right width goes into the right notch lest you force it and bend or break something. Just before the tabs enter the notches, make sure the wiper is orientated such that the long contact is on the wire-wound section and not jammed behind the brass rivets or raised ceramic tab between them. When all is aligned, carefully replace the metal hoop into its two holes such that its legs lay in their respective grooves in the ceramic half. Give the shaft a twist and, if you've a multi-meter handy, check to see that the resistance is adjusting smoothly.

Reinstall the potentiometer back in the crossover and solder the wires to their respective tabs. If you solder to the wrong tabs, the resistance will either be constant (twisting the knob makes for no sonic change) or it'll adjust inversely to the other controls, ie, turning clockwise will reduce the drivers' output rather than decrease. If all matches up to the notes you took before hand, then you're set.

Enjoy the music.

- JP

*Sometimes the wiper contacts have experienced sufficient pressure over the years to flatten out thus making for a loose feeling potentiometer and poor contact. With these, you may carefully bend the wiper contact and backer such that they exert more pressure and make for a tighter turning potentiometer. Just make sure not to bend too much or the pot will either be difficult to reassemble or adjust.

Did someone get e new camera? I can actually see this pix.

Hehe, yep. I received a Nikon Coolpix 990 as partial trade for some gear a little while back. It may be an older camera, but I'm still having a lot of fun being able to take pictures that don't look like those of UFOs and Sasquatch. Now I'm taking lots, but it's hard to resist the temptation to post them, such as sequences showing woofer refoaming and such.

- JP

Tremendous job, and awfully nice of you to bother to write all that down JP.

Jorge

Um, no, it was a very simple job and minor overall as these potentiometers were designed for maintenance. The thing is that most all of these units need cleaning now and people who've enjoyed their vintage Infinities are now finding themselves with non-functional speakers. I've seen many posts at various places regarding this and the desire to purchase replacements that are not too common anymore. I just wrote this up in the hopes that it'll help these people.

Besides, it is how-tos and informative posts that draw new people to forums via search engines, but the community that makes them want to come back.

- JP