TONYTANG

TONYTANG · November 2018

I have ACOUSTIC 626 Speakers which have seldom been used for many years. Now that I would like to get regular use, I found that the Tweeter and Midrange Speakers do not work.
The problem has to be with one of 3 items, capacitors, Fuse or some gadget that rotates in the back of the speaker, how do I test these. Thinking that it might be a Capacitor problem, I purchased 2 of similar readings - cannot find identical replacements here in England - I held the new capacitors (not soldered) by hand with corresponding wires but still no sound from the mentioned speakers. I have tested these two speakers at low volume with the Bass wiring and they work, so the problem is with the other 3 items. I opened the Fuse container (Red Button in the back) but it does not look like a normal fuse. The other 2 "Rotating" items in the back, I am unable to dismantle it open to see what it does and if anything looks out of order. Can someone give me any idea of what I should do .
Thank you

Emlyn · November 2018

Welcome, Tony. Seems you are referring to Acoustic Control 626 speakers. I am not familiar with those speakers myself, but other forum members are and can offer advice. You may have seen this thread already...

https://forum.polkaudio.com/discussion/179302/acoustic-control-corp-626-any-info-out-there

You may want to post your questions about the speakers in that thread.

pitdogg2 · November 2018

Gadget that rotates is an L-pad. Might try a electronics contact cleaner. Other than that i have nothing else to offer. Visit the link @Emlyn found there may be a nugget in there that is very useful.

TONYTANG · November 2018

Thank you PITDOG, now I have read up on what an L-Pad does, so far , I am unable to open up the L-Pad to clean it inside.

pitdogg2 · November 2018

TONYTANG wrote: »

Thank you PITDOG, now I have read up on what an L-Pad does, so far , I am unable to open up the L-Pad to clean it inside.

No holes in it?

mhardy6647 · November 2018

A (variable) L-pad is two variable resistors, one in series with the load (speaker driver or system) and the other in parallel to the load. This permits attenuation without changing impedance -- very useful in a speaker system, since an impedance change would alter the characteristics of the crossover network.

https://www.diyaudio.com/forums/multi-way/250292-benefit-fixed-resistor-lpad-variable-lpad.html

Because they are devices designed to pass fairly high levels of power (essentially two rheostats in one package), dirty (oxidized) L-pads aren't always amenable to the traditional "squirt and hope" cleaning with a good contact/control cleaner (e.g., CAIG DeOxit) that one would typically use on a normal potentiometer or switch. This being said, it shouldn't hurt to clean one that way, and it might help. No guarantees though.
EDIT: Here, FWIW, is a tutorial of sorts on using DeOxit to clean hifi switches and controls:
http://audiokarma.org/forums/index.php?threads/the-idiots-guide-to-using-deoxit-revisited.207005/

The AR speakers use rheostats instead of L-pads, but the following link illustrates the "proper" procedure to clean a wirewound rheostat. This "should"

work for an L-pad, too, if the L-pad isn't "too far gone" (i.e., severely corroded or physically worn out).
http://audiokarma.org/forums/index.php?threads/acoustic-research-potentiometer-restoration-guide-very-long-with-photos.306818/

Finally, L-pads are readily available from folks who sell speaker building/repair supplies. In the US, here's a popular vendor.

https://www.parts-express.com/cat/speaker-l-pads/306

Here's an L-pad serving suggestion

source: http://www.usspeaker.com/px-Lpad-1.htm

IMG_0340 by Mark Hardy, on Flickr

mhardy6647 · November 2018

If you have a "battery" (i.e., a cell, like a 1.5 volt "flashlight battery") and a couple of pieces of wire, you can safely test the midrange and tweeter drivers independent of the crossover.

Each driver should be disconnected from the crossover to test.

Connect (or hold) one wire to the "-" terminal (actually, either terminal, for this test, it doesn't matter!) of the speaker driver and then connect (hold) the other end of that wire to the "-" pole of the battery. Hold the second piece of wire to theother pole of the battery. Now, while holding everything tight

, touch the free end of that second wire to the "+" (other) terminal of the speaker driver. The instant the circuit is "made" you will hear a little "static" (scratchy) sound as the battery energizes the speaker's voice coil and deflects the speaker's diaphragm.

Don't leave the battery connected for too long, because current will flow through the voice coil in the speaker under test, heating it and also draining the battery.

If the speaker driver is "bad", you won't hear anything.

The other, better (sort of!) way to test the speaker driver is with a "DMM" (digital multimeter) or an older VOM (volt-ohm meter), if you have one. Same procedure as the battery, except that you'll read the DC resistance of the voice coil in the driver directly. It should be a small but nonzero value (e.g., maybe about 6 ohms for an "8 ohm" speaker). If it is "infinite", the voice coil is 'open' (damaged or burned open).

Hope this is helpful!

PS Here's a video that may be helpful. This person uses a 9 volt "transistor radio" battery. This may be a little more convenient, but the higher voltage and current capacity of such a battery will be more stressful on the delicate voice coil of a midrange or tweeter. A 1.5 volt cell is a better choice, I'd opine.