Cleaning AR9 Driver Level Switches

[deek]

Greetings!

I have several pair of vintage AR loudspeakers, my favorites are the AR9's I just re-purposed in my living room as the main speakers in my 7.1 surround system. I wasn't surprised to find the foam rotted and completely destroyed on the 12" bass drivers as I replaced the surround on the 8" midbass drivers shortly after I acquired them.

For the purposes of my surround system, I intended to simply use the top binding posts and use the upper-end along with a subwoofer for the time being.

I was surprised, however, to find that the level switches are causing intermittent connections and drivers are dropping out occasionally. Selecting a different attenuation value will occasionally cause that driver to drop out completely. Wiggling the switch or otherwise disturbing it will usually return the driver to it's normal operation.

While I have the 12" drivers out to restore them I plan to repair the switches. I have searched this excelent site and found several references to AR9 restoration threads, but none detail how the switches are removed from their bezels.

Does anyone have some detail about how this is done? I can't see far enough into the enclosure to tell how the switches come out and I don't want to just yank on them and hope they come out... 30+ years is not kind to most plastic of course.

Thanks in advance for any help; I can't wait to get my surround replacement kits and get these things back to their former glory!

-deek

[ar_pro]

It's pretty simple, Deek - you'll need to carefully work a sharp blade (like an X-axto knife) along the edge of the metal bezel to work it loose.

Each bezel is held on by a light amount of glue, and will pop off undamaged, if done with care.

A nut holds each switch in place, and you can access the switches through the woofer hole - the resistor board is held in place by the nuts on those three switches.

Look at the AR-9 blueprint in the Library, and you can see what you'll be dealing with.

Touchy switch contacts are not unusual - this is one of the few weak spots in the AR-9 design, but the good news is that I've never seen a completely dead switch, so you should be able to get them working properly.

[deek]

See there? I would never have thought to remove that piece from the outside of the cabinet. I'll do some photos of the process; maybe what I learn will help others.

Thanks, ar_pro. I'll give this a shot this weekend.

-deek

[deek]

Ordered my surround kits from Simplyspeakers yesterday so I decided to get started... This has been much less complicated than I expected, but I'm going to detail my work here and hopefully someone can benefit.

Removing and cleaning the driver level switches on an AR9

Step 1: Getting at the switches

In order to reach the switches, you have to remove one of the bass drivers from the cabinet. There are 6 screws total. Once you get the driver out, remember to mark the terminals so you don't get them out of phase:

Here's what you're trying to get out of the cabinet. It's a substantial PCB with four wire terminals, half a dozen resistors and the three DPDT switches soldered on.

This is a view looking up from the floor towards the front of the cabinet. Nothing holds this PCB to the cabinet but the threaded post on the three switches so all you need is to remove the nuts from the posts and the whole thing slides out.

Step 2: Remove the bezels around the switches

Use a thin, flat blade to slide under the bezel surrounding the switches. Pry very slightly upwards in a couple of spots and you'll be able to get your fingernails underneath the edges. They're made of metal and not aggressively glued, so don't worry about damaging them.

Step 3: Remove the nuts and washers from the switches

First, set the switch to the middle position (-3db) to keep it out of the way of your tool. Use a pair of needle-nosed pliers to remove the nut from the post on the switch. These are not terribly tight so no wrench or socket is really necessary.

Once you have all three nuts off, the board will be loose in the cabinet, but will not fall out, so no need to support it from inside.

Step 4: Remove the board.

Reach into the bass driver mounting hole and up to the switch board. Press from the outside on the switch posts (not the handles) each one in turn so the board doesn't bind. Wiggle the board a bit and it will come out easily. Take a photo, or mark the board now to make sure you get the wires back in the right spot. [edit] I just noticed the PCB is labeled with the wire color, so don't worry if you didnt' mark them [/edit]

Use pliers or your fingers to gently wiggle the wires off their terminals. Congratulations, the board is out! Here's what you're up against:

Not too much to it, huh? This board simply contains two resistor values that are part of the crossover. The far right switch position delivers full signal to the driver, the other positions first pass the signal through a resistor of varying value then to the driver.

Step 5: Clean the switches

There is some debate over what is the best way to clean a switch of this size. Most agree that a good contact cleaner sprayed down the barrel is sufficient. Some argue that the oxidation is not effectively removed in this way and should be mechanically cleaned by disassembly and crocus cloth or sandpaper.

My method is to use a tube on the contact cleaner spray head and rock the switch to one side then spray a small amount in while pressing the handle in toward the switch. Rock the switch to the other side, give it another quick spray and then exercise the switch continuously for a minute or two.

If you have access to compressed air, you should direct some air past the handle down the post to blow out any loose material. Canned air works too.

Let the whole thing dry for several hours before putting it back in service.

Assembly is the reverse of disassembly. Note that the cut off corner faces the bottom of the cabinet. I used three small dots of hot glue on the bezels to re-attach them.

Good luck!

[ar_pro]

Nice work, deek - the photos are excellent, and clearly show the process for anyone troubled by an intermittant AR-9 switch.

[deek]

Thanks! I'll continue to edit as I re-assemble... for instance, I had to go back to the photos today to see in which orientation the board goes. Also, I think you may be able to clean the switches in-place but you would have to protect the lower part of the speaker to prevent the cleaner from getting on the wood. That is some nasty stuff!

-deek