Notes on the Troubleshooting and Repair of Audio Equipment and Other Miscellaneous Stuff


  4.18) Tape speed problems on older equipment

Older reel-to-reel decks (maybe even some cassette decks) likely use an AC
induction or synchronous motor driven from the power line.  Speed selection
is usually done by switching in different sets of motor windings and the use
of slip-on capstan/pinch roller sleeves.

Speed problems are most likely a result of

* Decayed rubber parts - belts, idler tires, pinch roller.
* Gummed up lubrication or worn bearings.
* Dried up or otherwise faulty capacitors in the motor circuitry.
* Faulty switches or wiring in associated with speed selection.
* An actual bad motor is possible but not that common.

See the appropriate sections in the chapters: "Turntables" and "Motors and Relays" for specific information on these types of problems.

  4.19) Tape speed adjustment made easy

OK, you have found the magic screw, but how to set the speed accurately?
Sometimes, there will be strobe disks on tape decks which will appear
stationary under fluorescent lighting (magnetic ballasts only - electronic
ballasts are usually high frequency and do not modulate the light intensity at
the power line frequency) but not usually.  So, you do it by ear:

Make a recording of a single tone on a tape recorder you trust - one
with accurate speed.

Suitable sources include:  a signal generator, electronic instrument,
Touch-Tone phone tone, PC sound card output or PC speaker, etc.  A frequency 
around 400-1000 Hz should work well.

Then, adjust the speed while listening to this same source simultaneously
with the tape being played back on the unit to be adjusted.  As you adjust
the speed, you will hear the pitch change.  As it approaches the correct
setting, you will hear the tones beat against each other.  When you are set
correctly, the pitches will be equal and the beat frequency will go to zero.
Even if you are tone deaf, you will easily be able to adjust pitch accuracy
to better than 1/10 of a semitone using this method.

Recording the 60 or 50 Hz power line (through a suitable isolated attenuator) 
and using this as a test tone will work if you have an oscilloscope.  Trigger
on 'line' and adjust playback speed to stop the trace from drifting.  However,
this is too low a frequency to be used accurately with your Mark I ears!

Some alternatives:

(From: Helling Bernie (helling@uwindsor.ca)).

A while ago I hit upon a way to set the speed on old cassette decks that
have gone out of speed. 

Use an electronic guitar tuner

They cost about $40, can be borrowed, etc...  Find a pro cassette deck that
is in speed, (the local campus radio station had a nice one)  and record a
tape full of A tone. My guitar tuner puts out tones too, so that was easy....

Play the tape in the suspect deck, while adjusting the motor trim to
replay a A tone perfectly on the tuner meter...


I never did have the patience to learn to play the guitar, so I got some use
off the tuning meter....

(From: Paul Temple" (mri@earthlink.net)).

Get a song on CD and a tape of the same album.  Play both at the same time
and adjust away!

  4.20) Sudden increase in flutter on tape decks or Walkmen

If your prized Walkman suddenly develops a severe case of warbling
sound check:

1. Batteries (where appropriate).  Almost dead batteries will greatly
   increase flutter.  Use of Nickel-Cadmium rechargeable batteries in
   place of alkalines may result in problems due to their lower voltage
   (1.2 V vs, 1.5 V per cell).

2. Tired belts - loose flabby deteriorated belts will produce varying,
   probably slow, speed as well.

3. Dirt or goo on pulleys.  Sometimes a glob of stuff gets stuck to a
   pulley and produces a periodic variation in speed.  I picked one up
   at a garage sale that had this problem.  I thought it was a bad motor
   until a careful examination revealed that the belt was jumping a mm
   or so on each rotation of an idler pulley.

4. Lack of lubrication - a dry or worn bearing may result in a variety
   of speed problems.

5. Bad speed regulator - either mechanical or electronic including
   bad solder connections or cracks in circuit board traces.

6. Bad power supply.

7. Bad tape.  Don't overlook this obvious possibility, try another one.

  4.21) Annoying tick every 30 seconds or so from audio output

This may be an almost inaudible tick, click, or pop which occurs fairly
regularly.  Its frequency may be dependent on many factors including
temperature, humidity, even whether you are at the start or end of a
cassette!  I may occur even if no cassette is present but the motors
are running.

The tick is probably due to a static discharge though other causes are
possible including mechanical problems and bad capacitors in the power

(From: Paul Grohe (grohe@galaxy.nsc.com)).

The problem is with a plastic or nylon gear, in contact with a
rubber belt or tire, generating a charge and discharging to some
nearby metal.  (It acts just like a miniature Van De Graff
generator --- sam.)

You have to listen around for it.  Murphy sez it will probably be
buried deep in the "guts" of the machine ;^)

I found it by touching a small wire to each of the pulleys until
it stopped "snapping" (actually, I got a little "snap" when I found it).

My "cure" was to use some stranded wire to create a "brush" that lightly
brushed against the pulley to bleed off the charge to the chassis.

I would first check the two big capstan flywheels and anything
powered by the main motor belt.  Look for any plastic, or metal
with plastic bushings and parts in contact with belts or tires.

(From: Ylo Mets (ylo@mango.mef.ki.se)).

I have experienced similar ticking in an old two-motor deck. There was some
dust collected between the takeup/wind motor shaft end and the metal chassis,
which evidently generated static electricity. Cleaning the dust did the trick,
although at first I thought the shaft was too close to the metal chassis. You
can check for the static by breathing slowly into the mechanism. The damp air
should discharge the static and the frequency of ticks decreases. Such ticking
is especially annoying because it is not exactly regular.

  4.22) Reel-to-reel tape deck problems

"I have a Teac 2300S reel to reel. 7" reel capacity, 1/4" tape. Two
 problems. First, right channel doesn't play back. Second, pinch roller
 doesn't come up to the capstan unless it's gently pushed."

(From: Davetech (dnesbitt@mindspring.com)).

I've repaired a few reel-to-reels in the past and generally find that they
all need three main things done:

* They need all the rubber parts - belts, tires, rollers - replaced.  Also the
  brake pads.

* They need all the controls and switches cleaned with a de-oxy type cleaner.
  (This may be the cause of your right channel problem).

* They need all the mechanical pivot points cleaned and re-lubed.  (This may
  be the problem with your pinch roller).

The last one I did, the old grease had hardened up so much that the heads
would not come up to contact the tape - and the grease was so hardened that
I could not get the linkage pulled off even using pliers and pulling as hard
as I could. I had to heat the post with a propane torch before the old grease
would soften enough that I could separate the parts.

I put enough time in the last unit that I could have fixed 3 or 4 VCR's, so
I'm not real big on taking them in.  They are generally very time consuming
to disassemble and reassemble and overhaul. But not usually technically
difficult to fix.

  4.23) Tape creeps off capstan

"I have a Sony reel-to-reel tape recorder.  When I play a tape, after a few
 seconds or minutes of playback, I can watch the tape creeping up the capstan
 between the rubber roller until it comes out the top and off the capstan."

The first thing to check - as with a VCR with similar symptoms - is the
condition of the rubber parts, in particular, the pinch roller.  Next, would
be tape path alignment and wear:

(From: Jack Schidt (dbutler@airmail.net)).

Check the reel height as well.  Capstans are upset if the reel tables have
shifted.  Use a straight edge between the two reel tables.  There are set
screws that sometimes get loose on some of these machines.

Check for a worn capstan bushing.  Disconnect the drive belt (if any) and see
it there is lateral play in the capstan.  If so, perhaps you can shim it
(either the motor [if equipped] or the idler).

Also make sure the tension is simply not too high.  You should be unable to
pull the tape through, but ridiculous force (as in something is BENT) will
cause this problem as well.

  4.24) 8-track player problems

These compete with turntables for classification in the Jurassic era.  8-track
equipment uses a cartridge with a single reel and enless loop tape (tape is
pulled from the center and returned to the outside).  The tape can only move
in the forward direction - rewind is not possible.

There were also similar competing but incompatible 4-track systems as well
as quadraphonic 8-track (when quad was all the rage).

Four pairs of channels allow for many hours of stereo playback without
changing cartridges.  A pair of playback heads is mechanically shifted
among the 4 possible sets of tracks when a metallic strip on the tape passes
over a set of contacts which operate a solenoid.

Most common problems are - you guessed it - mechanical with the cartridge or
in the drive or head shifting mechanism.  General comments with respect to
cassette decks apply here as well.

If you are really interested in resurrecting that 8-track player found under
the steamer trunk in your aunt's attic, there are many links to information on
8-track equipment, books, history, dealers, collecting, and everything else
8-track related that most people probably don't care much about anymore at the
following web site:

    * http://www.bway.net/~abbot/8track/resource.html.

There may be links for specific 8-track player repair information but I could
not locate them at this site.

However, this one seems to be the place to go for step-by-step 8-track
cartridge repair:

    * http://www.geocities.com/Paris/4831/       (Jeremy Larsen's Web Page)

  4.25) Repairing a cassette tape

(From: Filip "I'll buy a vowel" Gieszczykiewicz (filipg@repairfaq.org)).

This will be either easy or very hard. Question: do both of these have SCREWS
holding the tape together? If yes, EASY, if not, very HARD!

See what I'm getting at? Go to the store and get a quality tape that ALSO has
screws holding it together... you will transplant the insides into the new
cases. Take off the screws from both (old and new tape, do it one tape at a
time). Remove both top covers - make sure you don't lose the thin plastic
"lubricant" sheet (if any). Swap the tape reels - BE VERY SURE the old one
doesn't go flying off or it's more or less toast. Put the old tape reels into
the new case, make sure the tape follows the same path as the one you took out
did - so it doesn't get trapped by the case when you replace the top.  Put the
"lubricant" sheet back on top of the two reels of old tape and replace the
top. Put in all 5 screws. There you go. I'd say that this is 100% successful
every time I've tried it.

If your tapes don't use screws but are, rather, glued together, you're on your
own. I suggest a VERY sharp utility knife but tape damage is, alas, a very
REAL possibility.

Another way you can do this if you want to also replace the REELs (or if it's
a sealed unit) is to rewind the old tape, cut the tape LEADER and attach it to
the new cassette that you have already gutted. Put the new tape together (2
screws will do) and attach a small motor to the takeup reel. When the tape has
been transfereed to the new reel, cut it off the old one (the old cassette is
now empty) and open the new one again, attach the tape to the reel and put it
back together using all screws. Other than the leader being 2" shorter, you
have the old SOUL in a new BODY.

Of course, watch out that you wind the tape EXACTLY as it was and not on the
other side... etc. etc. I have done this twice. Grrrr.

It's a pain in the rear... so do it only if you have to...  I wouldn't do this
for money..... if that tells you anything.

Chapter 5) Turntables

  5.1) Turntable (record changer) maintenance

Here are general comments on oiling dinosaurs, oops sorry, turntables.

Usually there is a 'C-clip' or 'E-clip' which holds the platter (the thing
that rotates) onto the spindle.  It may be covered with a decorative
piece which can be easily removed.  The clip can be pryed off (gently)
with a small screwdriver (just don't lose it, though even this is not
a biggie so long as you never turn the thing up-side-down).

The platter can then be lifted straight up and off the spindle.  You will
see several things (this will vary depending on your particular unit):

1. A flat washer, sitting on a ball bearing race sitting on another flat
   washer (one or both of these washers may be missing.  Also, the top
   one may stick to the platter when it is removed.)  The ball bearings,
   shaft, washers, etc. should all be cleaned with degreaser and then
   lubed with a light grease.  If either the steel balls or the flat washers
   are corroded, replacement will be necessary or else there will be terrible
   audible rumble.  For now, it will at least work well enough to determine
   what else, if anything, needs attention.  Also clean and lubricate the
   platter bushing (center hole) and shaft (vertical post on which it rotates).

2. Changer gears etc.  These will have varying amounts of grease on them
   if it is not gummed up, leave them alone.  Put a drop or two of light
   oil on the shafts.  Inspect other linkages as well.   If the grease is
   gummed up on the gears or sliding linkages, you will need to clean it
   off thoroughly with degreaser and then use a small amount of high
   quality grease suitable for delicate mechanisms.  One cause of a changer
   failing to activate at the end of a record is gummed up grease.

3. Motor.  Check to see if the motor shaft turns freely and smoothly even
   if spun quickly between your fingers.  If it does - without squealing,
   don't do anything else.  If it is tight or makes noise, then you will need
   to carefully disassemble the motor and clean and lubricate the bearings at
   each end with light oil.  Don't lose any of the various washers/spacers that
   may be present on the shaft as it is removed from the end pieces and
   make sure to lubricate and return them to exactly the location and
   the same order they were in originally.

4. Clean the rubber parts with isopropyl alcohol and Q-tips or a lint free
   cloth until no more black stuff comes off and then dry thoroughly.  Now,
   inspect the belts (if any).  If belts are flabby or cracked or if they don't
   instantly return to their relaxed length if stretched 25% and released,
   they will need replacing.  Check the idler tire (if present).  If hard or
   cracked, it will need replacing as well.

Note: Light oil here means electric motor oil or even 3-In-One but NOT WD40.
Light grease means something that is suitable for fine mechanisms and is safe
for plastics.  Automotive bearing grease may not qualify.

  5.2) Speed control in turntables

Most inexpensive turntables/changers will use a synchronous motor or even
just an induction motor.  The only maintenance for the motor is cleaning
and lubrication.

Servo controlled turntables utilize a feedback technique which locks the
platter speed to a stable reference - either the power line (50/60 Hz) or
more commonly a crystal oscillator.  Here is one example:

A Sony turntable I repaired used a magnetic stripe pattern on the inside of the
platter which was sensed by a magnetic pickup.  The resulting signal was phase
locked to a stable reference and used to control a brushless DC direct
drive motor.  Speed would become erratic if (1) the magnetic pattern
were damaged, (2) the pickup position was moved too far from the surface
of the platter, (3) the Hall-effect sensors in the motor were bad, or
(4) the control electronics went bad.  In one case, it turned out that
one of the Hall effect sensors had failed in the motor.  This required
disassembling the motor and replacing the sensor - $4 from Sony.

  5.3) Turntable runs slow or fast after being moved

This is likely to be a mechanical problem - a belt that has worked loose and
is riding on the rim of the motor pulley or the wrong surface of the platter.

For an AC line driven motor (no electronics between the AC line and motor
except possible for a power transformer), it is virtually impossible for any
fault to result in a motor running faster than normal.  A motor may run slow
due to dirt, lubrication, or bearing problems.

Of course, check to see that any speed selector has not been accidentally
moved to the '16' or '78' position!

For a servo-locked turntable, a misalignment of the sensor used for speed
feedback could result in an incorrect - probably higher than normal (and
uncontrolled) speed.

  5.4) Wow, flutter, and rumble in a turntable

Wow and flutter refer to undesirable periodic variations in pitch caused by
changes in turntable (or tape deck) speed.  Wow would be a slow variation
(e.g., once per rotation) while flutter would be rapid (e.g., a motor
pulley with a bump).  Even if very slight, these faults will be all too
obvious with music but may go undetected at much higher levels for voice

Rumble is a very low frequency noise added to the audio caused by vibration
due to cheap, worn, dirty, or dry spindle bearings or by vibrations coupled
in from some other motor driven component or even from loudspeakers if the
volume is turned way up.  If really bad, rumble may sound like a freight train
in the next room.

For anyone only used to listening to CDs, even very small amounts of and of
these will prove very obvious and extremely objectionable.  Wow, flutter,
and rumble are undetectable - for all intents and purposes nonexistent -
with even the cheapest junkiest CD player.

For a common motor driven turntable, the following are likely causes:

1. Bad belt or idler.  Rubber 'rusts'.  If it is old, then almost certainly
   the rubber parts have deteriorated and will need replacement.
   Unfortunately, replacement parts are not as readily available as they
   once were.  The places listed at the end of this document may have some
   and there are many other sources but it is not as easy as one would like.

2. Dirty or worn spindle bearing.  This will cause rumble.  The thrust
   ball bearing can be cleaned and lubricated or replaced.   The platter
   bushing can be cleaned and lubricated.

3. Lump of crud stuck to motor pulley or idler, usually of unknown origin.

4. Dried up lubrication in motor, idler, or other rotating part.
   These can be cleaned and lubricated.

5. Bad motor (not that likely) except for lubrication in which case
   the motor can be disassembled, cleaned, and lubed.

6. Physical damage to platter - something heavy was dropped on it upsetting
   the delicate balance.

If you are attempting to restore a 20 year old turntable from Aunt Annie's
attic, don't even bother to power it up before replacing all the rubber parts
and cleaning and lubricating the motor, idler, and spindle bearing.

  5.5) Erratic sound from turntable

Sound that varies randomly in intensity or where one channel drops out
will usually be due to bad connections in the various units.  This could be:

1. At the pickup itself.  There may be small press fit connectors at the
   cartridge.  These sometimes become loose.  Gently remove each one
   (one at a time! so that you do not mix up the wiring) and squeeze with
   a pair of tweezers or needlenose pliers.  Snap in cartridges may have
   dirty contacts the springiness may have disappeared.

2. At the RCA plugs under the turntable which connect to the tonearm.
   Depending on your design and problem, you may need to simply clean
   with contact cleaner or squeeze the metal shell or center contact.

3. At the receiver, preamp, or amplifier.  Same as (2) above.

4. Sometimes the cables themselves will develop broken wires at one end
   or the other.  Easiest is to try a different set of cables.

  5.6) Turntable tracking and skating force adjustment

Tracking force keeps the stylus in the record's groove.  Too little is
as bad as too much.  It is best to follow the recommendations of the
cartridge/stylus manufacturer.  If you do not have this information, start
low and increase until you eliminate skipping or excessive distortion,
buzzing, or stuttering.  If too low, the stylus will make only partial contact
with the groove during high amplitude segments - it will jump from peak to
peak (or other portion) of the wave rather than smoothly and continuously
following it.  If too high, it will gouge the vinyl (or the shellac or
whatever depending on the vintage of your records) or in extreme cases,
bottom out on the cartridge's suspension.

Skating force compensation is applied to compensate for the fact that
except at one distance from the spindle (or with a linear drive tone
arm where this does not apply), the tone arm is not tangential
to the groove.  Imagine a perfectly flat record without any grooves.  If
you 'play' this, the tone arm will be stable at only one position somewhere
in the middle - where a line drawn through its pivot point and the stylus
is just tangential to a circle at that distance from the spindle.  The
skating is usually a simple spring which attempts to compensate for this
in such a way that the side force tending to move the stylus is minimized
at all positions.  Otherwise, the inner and outer walls of the groove
will experience a different force which will add distortion and affect
stereo separate and balance.

Skating force compensation is usually set based on the tracking force.

Note that if you are used to CDs or high quality cassettes, all the horrors
of records will be all to obvious unless you are using high-end equipment
(the kind that likely costs as much as your automobile) and meticulously
maintain your vinyl record collection.  Sonic defects like wow, flutter,
rumble, distortion, noise, imperfect stereo separation, skipping, and limited
frequency response are all facts of life for this technology which has not
changed in any fundamental way since Edison's time.

  5.7) Turntable tracking/skating problems

(From: Bill Turner (wrt@eskimo.com)).

You're bringing back memories.  I used to work for the leading Magnavox
warranty repair station in Los Angeles and I've repaired hundreds of the good
'ol Micromatics.  

Assuming there isn't something actually *pulling* the arm across the record
(in other words it's just sort of sliding across on it's own) the problem is
almost always the needle.  Either the tip is worn out, broken, missing, etc or
it could have just been dislodged from it's holder.  Lift up the arm and look
carefully at the needle.  The actual diamond tip is on the end of a short
shaft which in turn rests in a fork-shaped rubber holder.  This shaft is
easily knocked out of the holder, and if that's the case, just carefully put
it back.  

Hope this helps.  The Micromatic was a fine record player in it's time.  Good
luck, and let me know if I can help some other way.

  5.8) About stylus wear

So you still have one of those modified potters' wheels on which you place a
pre-formed piece of plastic that looks like a flattened dinner plate with a
hole in the middle and drag a needle over its surface to produce sound.  How
can you tell when the needle, err, stylus, has worn to the point (no pun...)
of requiring replacement?

It used to be that you could take it to any record store.  They would look at
the stylus under a microscope, and after a few choice utterances of "Oh my!"
followed by "This will strip the music right off your LPs", and would then
tell you that your stylus required replacement IMMEDIATELY whether it did or
not :-).  Of course, record stores don't exist anymore.

If you have a semi-decent microscope, you can do the same and get an honest
answer ;-). 100X should be more than sufficient, though getting the stylus
into position to view it may prove to be challenge.

The tip of a good stylus looks smooth and is spherical or ellipsoidal in
shape.  A worn stylus will exhibit edges/corners due to the wear of the tip.
Yes, even diamond will wear down if you drag it over thousands of miles of
vinyl.  Some of your LP record jackets may even have typical photos of good
and worn styli so check these out as well.

If the stylus is visibly worn:

1. The physical result will be that it will grind away at the grooves in your

2. The audible result of a bad needle will be excessive distortion and loss
   of high frequencies from (1).

After you replace it, your old records will still never sound as good as
they did before because of (1) :-(.

  5.9) Changer won't cycle automatically

If it is a basic old fully mechanical record changer, this is usually due
to gummed up grease.  There is a large gear which gets activated to operate
the lift-and-place mechanism.  Attached to this gear is a small swinging
segment that gets jogged by the tone arm reaching the proper position.  The
grease gets gummy and prevents this.  You have to remove the platter.

If it is a fancier changer with fully electronic controls, then it may be a
sensor or something in the circuitry.

Of course, there was this one I recently worked on where some previous repair
person (I am using this term generously) had glued the moving parts of the
changer mechanism together so it could not possibly ever have worked again
(until I unglued them all).

Chapter 6) Loudspeakers

  6.1) Loudspeaker anatomy

In this document, we use the terms 'loudspeaker' or 'speaker system' to
denote a unit consisting of one or more drivers in an acoustic enclosure
perhaps along with a frequency selective crossover, tone controls and
switches, fuses or circuit breakers.  Connections to the amplifier or
receiver are via terminals on the rear.  The front is covered with an
(optically) opaque or semitransparent grille which provides protection
and improves the appearance (depending on your point of view).

A 'driver' is the actual unit that converts electrical energy into sound
energy.  Most drivers use voice coil technology: a very low mass coil wound
on a light rigid tube is suspended within a powerful magnetic field
and attached to a paper, plastic, or composite cone.  The audio signal
causes the coil to move back and forth and this motion causes the cone
to move which causes the air to move which we perceive as sound.

The typical driver consists of several parts:

* Frame - a rigid steel or composite structure on which the driver is
  constructed.  The frame holds the magnet and core, cone suspension, and
  connection terminals.

* Magnet - this includes a powerful (usually ceramic, AlNiCo, or rare earth)
  magnet including a core structure provide a very narrow cylindrical air gap.
  This accounts for most of the mass of a driver.

* Voice coil - a one or two layer coil of fine wire wound on a light rigid
  cardboard, plastic, or composite tube suspended within the air gap of the
  magnet and connected via flexible wires to the electrical terminals.

* Cone - a roughly cone shaped very light and rigid structure that does
  the actual work of moving air molecules.  The cone in a woofer may be
  12 or more inches across.  The cone in a tweeter may only be an inch
  in diameter.  This is the part of the driver you actually see from the
  front of the speaker system with the grille removed.  The center is
  usually protected with a small plastic dome.

* Suspension - a corrugated flexible mounting for the voice coil called
  a 'spider' and outer ring of very soft plastic or foam.  Together, these
  allow the voice coil/cone combination to move readily in and out as a unit
  without tilting or or rubbing.  For most designs, there is a certain
  amount of springiness to this suspension.  Acoustic suspension loudspeaker,
  however, use the trapped air in a totally sealed speaker enclosure to
  provide the restoring force.

Inexpensive 'LoFi' devices like portable and clock radios, many TVs,
intercoms, and so forth use a single, cheap driver.  Some have a coaxial
pair of cones but this does little to improve the frequency response.

HiFi speakers systems will divide the audio frequency spectrum into several
bands and use drivers optimized for each.  The reason is that it is not
possible to design a single driver that has a uniform response for the
entire audio frequency spectrum.  A 'woofer' is large and massive and
handles the low base notes.  A 'tweeter' has a very low mass structure and
is used for the high frequencies.  A 'mid-range' handles the mid frequencies.
There may also be 'sub-woofers' for the very very low notes that we feel
more than hear.  Some systems may include 'super-tweeters' for the very highest
frequencies (which few people can hear.  This may make for some impressive
specifications but perhaps little else.)

A 'crossover' network - a set of inductors and capacitors - implements a
set of filters to direct the electrical signal (mostly) to the proper drivers.

Various controls or switches may be provided to allow for the adjustment
of low, mid, and high frequency response to match the room acoustics more
faithfully or to taste.  Fuses or circuit breakers may be included to
protect the speaker system from intentional (high volume levels) or
accidental (amplifier output stage blows) abuse.

  6.2) Loudspeaker problems

If you have a high quality and expensive set of loudspeaker, then
the cost of professional repair may be justified.  However, if the
problem is with speaker systems you might not write home about, then
read on.

Playing your music system at very high volume levels, especially CDs
which may have peaks that way exceed the ratings of your loudspeakers
is asking for trouble - but you knew that!  CDs can be deceiving because
the noise floor is so low that you are tempted to turn up the volume.
A peak comes along and your speaker cones are clear across the county
(remember the movie 'Back to the Future'?).  Loudspeaker systems are
generally pretty robust but continuous abuse can take its toll.

Problems with loudspeakers:

1. An entire speaker system is dead.

   Verify that the connections both at the speaker system and at the source
   are secure.  Check circuit breakers or fuses in the speaker system.  Reset
   or replace as needed.
   Make sure it is not the amplifier or other source that is defective
   by swapping channels if that is possible.  Alternatively, test for
   output using a speaker from another system or even a set of headphones
   (but keep the volume turned way down).  Assuming that these tests
   confirm that the speaker system is indeed not responding, you will
   need to get inside.

   It would take quite a blast of power to kill an entire speaker system.
   Therefore, it is likely that there is a simple bad connection inside,
   perhaps right at the terminal block.  You should be able to easily 
   trace the circuitry - this is not a missile guidance system after all -
   to locate the bad connection.  If nothing is found, then proceed to
   test the individual drivers as outlined below.
2. One or more drivers (the name for the individual speakers in a
   loudspeaker enclosure) is dead - no sound at all even when you
   place you ear right up to it.  The cause may be a bad driver,
   a bad component or bad connection in the crossover network.  Test
   these components as outlined below.

3. One or more drivers produces distorted or weak sound.  Distorted
   may mean fuzzy, buzzing, or scratchy a various volume levels.
   Most likely this is due to a bad driver but it could also be a
   defective component in the crossover - a capacitor for example
   or even a marginal connection.

Getting inside a speaker system usually means removing the decorative
grille if it snaps off or unscrewing the backpanel and/or terminal block.
Use your judgement.  With the grille removed, you will be able to unscrew
the individual drivers one at a time.  With the back off, you will have
access to all the internal components.  If sealing putty is used, don't
lose it or expect to obtain some replacement putty (non-hardening
window caulking like Mortite is suitable).

Test the components in the crossover network with a multimeter.  These
are simple parts like capacitors, inductors, and potentiometers or reostats.
Confirm that any circuit breakers or fuse holders have continuity.

Test the drivers on the low ohms scale of your multimeter.  Disconnect
one wire so that the crossover components will not influence the reading.
Woofers and midrange drivers should measure a few ohms.  If their
impedance is marked, the reading you get will probably be somewhat
lower but not 0.  If possible compare your readings with the same driver
in the good speaker system (if this is a stereo setup).  Some tweeters
(very small high frequency drivers) may have a series capacitor built
in which will result in an infinite ohms measurement.  Other than these,
a high reading indicates an open voice coil which means a bad driver.
In a comparison with an identical unit, a very low reading would mean
a partially or totally shorted voice coil, again meaning a bad driver.
Except for expensive systems with removable voice coil assemblies, either
of these usually mean that a replacement will be required for the entire
driver.  Sometimes an open voice coil can be repaired if the break can be

To confirm these tests, use an audio source to power just the suspect driver.
Your stereo system, a small amplifier attached to an audio source, or even a
pocket radio (use its speaker output if the headphone output does not have
enough power) will suffice.  The resulting sound will not be of high
quality because you do not have the enclosure sealed and it is only one
of the drivers in the system, but it should give you some idea of its
condition.  Again, comparing with an identical unit would be another

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Written by Samuel M. Goldwasser. | [mailto]. The most recent version is available on the WWW server http://www.repairfaq.org/ [Copyright] [Disclaimer]