Question about Altec Lansing ADA 885 Computer Speakers

1 Answer

Humming in woofer

The woofer developed a hum. Not caused by cable inpur or bad connect. It appears that a filter cap may have failed on power supply. Where can I get a wiring diagram of the circuit board and a board component list?

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  • TomGa Oct 25, 2007

    Thanks for your response.

    I replaced the capacitors but still have the humming.

  • TomGa Oct 25, 2007

    Not sure how this got labeled as Solved as the problem still exists. Replaced the capacitors but something is still wrong. Any suggestions?

  • TomGa Oct 30, 2007

    I ordered additional caps and have replaced all of the larger caps. The hum is present without a signal input from the computer. In fact the hum is present with all inputs and all speakers except woofer disconnected and the diagnostics test button is pushed. I will be unavailable for about two  weeks starting later this week so it may that long before I could try another suggestion. Thanks for your assistance so far.

  • MC201 Mar 28, 2008

    My set was one of the first that Dell sold. My sub began the humming long ago and finally just quit working. The speakers work fine and sound great. Kinda hate to get rid of this system, but unless the fix is easy, it wouldn't make much sense to spend money on an almost 10 year old speaker system. I have never tried soldering on a circuit board and got absolutely no help when I contacted Altec Lansing. I'm cracking the case now to see if there are any swollen or leaking transistors.


  • r9x0 Jan 19, 2009

    The problem is is either resistors or diodes, near the power coupling on the circuit board in the lower cover under the unit.

    In mine, there is a partial burn mark, on the housing and the circuit board right where this pair of resitors or diodes are - I am certain they are the problem, but they are tarnished/burned enough that I cannot clearly identify them or thier values for replacement. - a real shame.

    Markings on the circuit board with arrows pointing to these components say:

    "Caution: For continued protection against risk of fire, replace with same type 125v, 1.0A

    Slow blow fuze.

    Curious - First, they must have had a known problem with these, to put this warning, with arrows leading not to the fuse, but to these two resistors/diodes.

    If anyone can properly identify these two components,

    our problems may be solved with a little soldering.

  • Mel999 Jan 24, 2009

    I just acquired an old set of Altec Lansing ADA 885 speakers and subwoofer, and it has the same problem. The speakers will work when the power is not connected, but the sounds is not amplified to any degree. When I plug in the subwoofer, things are still okay. But when I turn on the speakers the humming begins. I can still play music through the speakers, so loudly that it overcomes the humming...but it's too loud, and of course, who wants a humming sound? I am really bummed out because the speakers are really excellent. Much more powerful than the other two sets I have for my desktop computers. And I can hook my ipod up to these, of course. It's a shame to throw away good stuff...



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A wiring diagram could be difficult if not impossible to find but you should'nt need one anyway.

You're correct in saying it's most likely a filter cap in the power supply, of which would be a larger electrolytic cap that may even display signs of being faulty. Look for leakage of crusty brown stuff on the end where the rubber seal and leads are, or possibly the other end, shrunken plastic skin, bulging or other signs of over heating. Replace any you find that have visual signs of failure.

Sometimes you cannot tell by looking if a cap is bad but it would'nt cost that much to replace the larger ones in there anyway. Open up the unit, write down the electrolytic cap values
you find, go buy replacements and replace em.

You're hearing 60 cycle hum so the filter(s) you need to replace will be quite large physically and have a fairly high micro farad value....such as 1000, 1500 or 2200.

When buying replacements, get as close to the micro farad rating as possible and buy at least the same voltage rating, or higher. Be sure to solder them in correctly, there is a negative and positive lead and you dont want to get those reversed or....

** Please re-comment if the suggestion did not work for you, there may be several other possibilities.
** Please add a comment before giving a rating other than Solved

Posted on Oct 23, 2007

  • Patrick Wagner
    Patrick Wagner Oct 26, 2007

    I dont see any rating on this as yet.
    Humming is most always caused by bad filter capacitors but could also be a problem with voltage regulation, specifically ic's and transistors. It could also be a problem with a ground, which would most likely be on the cable, a broken wire to the plug.

    Before going to any more trouble, try the speakers on another computer. Is the hum present when the input lead is pulled out of the computer?



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I suspect you have a bad cable, a poor ground or a bad
power supply inside the speaker amplifier. The amplifier
(inside the sub-woofer) could also be defective.
1) Bad cable or connector:
If the (braided shield/outer tube) of the coaxial input cable is
not grounded, the cable will pickup line frequency "hum"
from surrounding power lines, house wires, lights and

This hum is then amplified by the speaker's amplifier
causing the constant bass sound you speak of.

Because the hum frequency fundamental is 60 Hertz in
North America, 50 Hertz in Europe, you hear it coming
mostly out of the sub-woofer, because the midrange and
high speaker circuits filter it out.

Check the input connectors, cable at both ends, wiggle
the jacks at a low volume setting to see if it changes.

Make sure that you are indeed using a properly shielded
coaxial cable.

A coaxial cable consists of a thin inner conductor, surrounded
by a flexible tube made up of a braided metal shield, which
must be grounded. This prevents hum from being picked up
by the sensitive amplifier inputs.

2) If the power supply within the sub-woofer's internal amplifier
is defective, the the power supply hum will also get coupled
into the amplifier and speaker with same results as above.

Power supply hum is typically twice the line frequency,
i.e. 120 Hertz, but not always, depending on what
component failed: Rectifier diode, filter capacitor, or
the voltage regulator.

3) Ground loops:
When you run very long cables between the source and
destination of an audio signal, multiple ground paths (must)
exist between the two points in space, creating complete
loop circuits.

Power line hum from the environment can (will) induce
heavy AC currents around these loops, creating a voltage
gradient across these cables, and in-between the end

Once again, this AC hum is coupled into the amplifier inputs.

Ground loops become a problem with cables over 10
feet long, and an astronomical problem for stage audio
engineers. To avoid ground loops, they must break
the circuit's continuity by using isolation transformers,
optical isolators, and/or differential input amplifiers.

So how long are your cables?

Most house stereo components are only designed to
handle 6 to 10 feet of cabling max.

30 feet is already asking for major trouble.

4) Feed back oscillation: This occurs when the output of
an amplifier is fed back to the inputs with a round trip
gain greater or equal to unity. The tiniest little electrical
disturbance is then amplified and re-amplified, over and
over again, usually at one preferred frequency, causing
the typical (ear-splitting) microphone squeal or howl.

In your situation feedback and/ loss of original signal
could be the result of mis-wiring the input cables.

Note that this is NOT as silly nor as unlikely as it sounds,
because many computer audio cards and even some
home stereo systems have re-configurable inputs and

SOFTWARE configuration decides which jack at the
back does what !!!!

On my computer, for example, the Realtek audio driver
tries to automatically figure out what cable is connected
to each jack (usually it gets it wrong)

Using the Realtek control panel applet, I can then
manually re-configure the gray jack as input,
the green jack as bass, pink jack as center.... etc.

If this situation also applies to your system, please check
the software configuration. Connecting an output cable to
an input jack will certainly cause a lot of HUM and not
much music.

5) Finally, don't rule out internal sub-woofer failure. Unlike
the passive stereo/hi-fi speakers of days gone by, modern
multi-channel theater systems with front, center, rear and
sub-woofer speakers are internally amplified, with active
frequency cross-over filters and special effect/ surround
sound capabilities.

Usually, the large sub-woofer contains most of the
electronics, amplifiers and filters.

It feeds the other speakers, and it is controlled by
an external volume control module which can be separate
or built into one of the tweeters.

These sub-woofer electronics are prone to poor design,
overheating and early failure. (Even fresh out of the box
like yours)

If you cannot get it working, take it back to the store,
and make the NICE salesmen **** with it.

Good luck
Please rate my answers

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