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


Chapter 14) General Equipment

  14.1) IC and hybrid power audio amplifiers

Note: troubleshooting of large audio amplifiers constructed with discrete
output stages is left to a separate document.  See: "BIG audio
power amps".

The audio amplifiers found in small radios, Walkmen, portable cassette
recorders, and other low power devices are often single chips with few
external components.  Obtain a pin diagram, test inputs and output(s) with
an audio signal tracer and/or oscilloscope.  A dead output where inputs
and power are present usually indicate a defective IC - as does one that
becomes excessively hot - assuming that the output is not overloaded.

Larger audio amplifiers may use ICs (up to 10 or 20 W) or hybrid modules
(up to 100 W per channel and beyond).  Purists may argue about the quality
of the sound from these compared to discrete component designs but they
are being used in many designs - at most price points (except perhaps the
stratosphere of audiophile land).

Hybrids modules (called 'blocks' or 'bricks' by some) may be totally self
contained requiring just power and line level inputs or may be just the
final stage in an overall system including external amplifier circuitry
which is  effectively a power op amp - high gain with negative feedback.
Failure of these bricks is quite common.

Note that testing of these op amp designs - whether discrete or brick
based - can be very confusing due to the high gain and feedback.
Intermediate signals in a working channel may look like power supply
ripple and noise.  In a dead channel these same points may appear to be
normal or highly distorted audio depending on which stage you test.  In
addition, since extensive negative feedback is used, power supply ripple
and noise is much less important significant and there may be substantial
amounts of both in a normally operating amplifier.

One of the bricks may be shorted resulting in a blown fuse or overheating
of other components.  It is usually safe to unsolder each of the hybrids
to determine if the other channel or at least other portions of the unit
come back to life and without blowing fuses.

With stereo amplifiers, it is normally safe - and most effective - to
swap components between the working and dead channels as long as you
are sure there is no short circuit on the output.  This is by far the
quickest way to confirm a dead brick.  (I would be a lot more reluctant
to make this recommendation for a large audio amplifier constructed
with discrete transistors in the final power stage as multiple cascade
failures are possibly and likely if **all** defective parts are not
located before power is reapplied.)

  14.2) Amplifier noise caused by bad hybrid bricks?

There can be all sorts of sources for low level noise or static including bad
connections almost anywhere, defective semiconductors, and erratic power amp
modules.  These are usually hybrid circuits - multiple devices mounted on a
common substrate and interconnected via a variety of technologies.  Think
of them as entire subsystems encased in plastic.

Thus, hybrid bricks may have problems with noise especially considering that
they may run hot and be abused by poor tastes in music (or at least high
volume levels).  Thermal cycling can take its toll on this kind of device.
If you have eliminated other likely causes, replacing the brick would be the
next step if the module is not that expensive -  how much do you value your
time and hair?  Of course, if there are separate bricks for each channel,
one channel is most affected, and the volume control does not affect the
level of the noise, the choice is clear - swap.  This will be relatively low
risk in most cases.  A hot air gun used carefully on the final modules might
also be a good way of inducing or changing symptoms resulting from marginal
connections or components.

  14.3) Andy's quick tips for locating shorted/bad amplifier parts

(From: Andy Cuffe (baltimora@psu.edu)).

If it has IC's for the audio output you can just remove one of them.  If
the fuse still blows try removing the other one.  If the fuse blows with
both output ICs out you know there are problems in an other part of the
unit, probably the power supply.

If it uses transistors instead of ICs you just need to check them with
an ohmmeter.  The bad ones almost always measure close to 0 ohms
between at least 2 of the three pins.  Once you find the bad pair try
the stereo with them removed.  You should get normal sound from the
channel with the good transistors.  To determine if there is more damage
to the amplifier you can swap the good transistors into the damaged
channel.  Before you remove anything WRITE DOWN where they go because
it's easy to get them mixed up.  I strongly recommend that you don't
bypass the fuse unless you don't want to fix it very much.  I have seen
a lot of repairable electronics ruined by this type of troubleshooting.

  14.4) Substituting Darlington transistors in audio amplifiers

(From Daan van der Veer (D.J.C.vanderVeer@stm.tudelft.nl)).

I have good experiences with the use of Darlingtons instead of normal output
transistors in audio power amplifiers.  The only problem is that you have to
readjust the bias current of the bases of the drivers.  Furthermore, reduced
or increased frequency response is almost always corrected by the amplifier's

Readjusting the bias current is very simple with a scope and a sine wave
generator, but could also be done with a simple voltmeter.  And a computer
is a very handy tool in diagnosing amps, if you have a soundcard, you can
(mis)use it to measure a frequency response of any everyday amp (frequency
response of most soundblaster compatible soundcards is 44 kHz). And with a
very precisely tuned high quality notch filter you can even measure the THD
of any amp, *real-time*.  (This is very handy if you want to adjust output
transistor bias current, to a minimum of crossover distortion).

  14.5) Noisy or intermittent switches and controls

Symptoms include audible noise when rotating knobs, erratic operation of
mode selectors, random changes in volume, switches, or controls that
need to be jiggled or tapped to make them cooperate.

The causes are likely to be either dirt or wear.

First, try a spray control/contact cleaner - even the stuff from Radio Shack
may make a remarkable difference iff (1) dirt is the problem and (2) you can
get the cleaner inside the troublesome part.

DO NOT use WD40 or a similar product because aside from the flammability
issues their use may result in rapid failure even if you get the immediate
gratification often provided by these sprays.  See the section: "Why NOT to use WD40 on noisy controls".

Some types of contact and control cleaners can be used safely with
low voltage circuits while they are powered but not always - read the
label directions.  Select a product that specifically states that is it
safe for switches and controls.

Use the extension tube that comes with the spray can and snake it into
or near any visible access holes.  Operate the control or switch to
help the cleaning action.  Don't overdoe it - if you get to the right
spot, a little is all that is needed.

Resist the urge to use sandpaper or steelwool (ack!) on switch or connector
contacts.  However, pulling a piece paper through a set of contacts or the
occasional gentle use of a soft pencil eraser (e.g., Pink Pearl) may be

If this does not help - or only helps short term - the part may be worn.
Sometimes, repair is possible (a slide switch with contacts that have
loosened with use, for example) but replacement is better - if you can
find an exact or suitably close match.  See the section: "Interchangeability of components".

  14.6) Why NOT to use WD40 on noisy controls

This may not apply to the resistive elements in all/many/most controls but
why risk it?:

(From: Richardson (rchvid7@flash.net)).

Here are some facts after seeing the results first hand in an environment
where Pro TV editors were using up controls in audio mixers manufactured by
Shure Brothers.  WD40 when used for the first time resulted in good operation
for 5 days.  After that time the controls started to deteriorate very quickly
and were junk the next week.

The situation was clear after opening up the pots afterward.  The carbon
material was bonded to itself and to the phenol substrate by some chemical
which became soft after being exposed to the hydrocarbon base of the WD40.  It
soon deteriorated to mush.

The use of LPS 1 did not cause such a dramatic failure of the surfaces but did
not provide any improvement that lasted.

In the past we could get good results with Freon cleaning spray, but it is
getting harder to get than the replacement controls.

In test pots the only way to get an improvement was to carefully remove
residue and relubricate with a lubricant like Radio Shack "Gel Lube" or the
latest Sony grease available for broadcast and pro use.

  14.7) Resuscitating potentiometers

(From: Rene Zuidema (cps_rjz@cistron.nl)).

Often, pots are not really dirty, but the pot wiper just worn out
the resistive layer. No amount of cleaning will solve the problem.

Just carefully re-bend the wiper contacts to follow another track
alongside the damaged resistive material. If done well, the wiper will
now track intact resistive material again. As new!

This specially works for servo's as used in RC cars / planes etc. In
these applications the resistive track around the servo neutral
position is worn out after some seasons of use.

(From: Paul Weber (webpa@aol.com)).

Disassemble the pot by carefully bending the tabs that hold the cover on
(assuming this is a cheap consumer type pot).  Inspect the works with a
magnifying glass; find the fingers on the rotor that touch the resistor
material. Using a needle or dental pick carefully bend the fingers out of
the furrow they've worn in the resistor material.  Objective is to make
contact with an unworn area on the resistor material.  Clean the whole
thing with spray cleaner and re-assemble.

Overall resistance may be slightly changed due to the lost resistance
material, but this is usually not a problem in consumer applications. 
Good luck!

  14.8) General intermittent or erratic behavior

Any intermittent problems that cause random sudden changes in performance
are likely due to bad connections, internal connectors that need to be
cleaned and reseated, or dirty switches and controls.  First, see the
section: "Noisy or intermittent switches and controls".

Bad solder joints are very common in consumer electronic equipment due both
to poor quality manufacturing where cost reduction may be the most important
consideration.  In addition solder connections deteriorate after numerous
thermal cycles, vibration, and physical abuse.  Circuit board connections
to large hot parts or parts that may have mechanical stress applied to them
are most likely be suffer from hairline solder fractures (often called
'cold solder joints' when they result from poor quality soldering at the
time of manufacture).  However, since the solder is often the only thing
anchoring these components, mechanical stress can eventually crack the
solder bond as well.

To locate cold solder joints, use a strong light and magnifier and examine
the pins of large components and components that are subject to physical
stress (like headphone jacks and power connectors) for hairline cracks
in the solder around the pin.  Gently wiggle the component if possible (with
the power off).  Any detectable movement at the joint indicates a problem.
A just perceptible hairline crack around the pin is also an indication of a
defective solder connection.   With the power on, gently prod the circuit
board and suspect components with an insulated tool to see if the problem
can be effected.

When in doubt, resolder any suspicious connections.  Some device may
use double sided circuit boards which do not have plated through holes.
In these cases, solder both top and bottom to be sure that the connections
are solid.  Use a large enough soldering iron to assure that your solder
connection is solid.  Put a bit of new solder with flux on every connection
you touch up even if there was plenty of solder there before.

In addition to soldering problems, check for loose or corroded screw type
ground (or other) terminals, and internal connectors that need to be cleaned
and reseated.

  14.9) Need to turn up volume to get sound to come on

If at times, it is necessary to turn the volume way up or possibly to tap
or whack the unit to get the sound in one or both channels to come on when
the unit is first powered up, the speaker protection relay could be faulty.
Receivers and audio amplifiers often include a set of relay contacts in series
with each output to protect the loudspeakers from power-on and power-off
transients as well as damage due to a fault in the audio circuits.  However,
these contacts may deteriorate after awhile resulting in intermittent sound.

While this set of symptoms could be the result of general bad connections or
even dirty controls or switches, the relay is often at fault.  This is
exacerbated by switching the unit on and off at high volume levels as well
as this may cause contact arcing.

To determine if the relay is at fault, either test it as outlined in the
section: "Relay testing and repair" or with the unit on, very gently tap the
relay to see if the sound comes as goes.  If the relay is bad, you can try
cleaning its contacts or replace with one that has similar electrical
specifications as long as you can mount is somehow.  Don't be tempted to
bypass the relay as it serves a very important protective function for both
the amplifier and your loudspeakers.

If it is not the relay, see the sections: "General intermittent or erratic behavior" as well as "Noisy or intermittent switches and controls".

  14.10) Speakers take a while to come on

You turn on your stereo receiver and everything appears normal - display,
tuning, signal strength, etc., but there is no sound.  A few minutes later,
just when you had entirely given up any hope, there is a click and everything
is normal - until the next time you power down.  The amplifier is taunting
you - hehe, I will come on when I feel like it!

(Note that if it never comes on, then there could be a real problem that the
protection circuitry is catching such as shorted components in one of the
power amplifiers.)

This sounds like the signal to power the speaker relays is not being generated.
The underlying cause could be a fault in the time delay or fault protection
(overload) circuit.

It could be as simple as a bad capacitor.  A first test might be to check
for an audio signal at the input to the speaker relay.  If there is signal
almost as soon as you power it up, then trace back from the relay coil to
see what type of circuitry is there.  A schematic will probably be needed
unless you find an obvious bad connection or dried up capacitor.

  14.11) Amplifier clicking and shutting down on music peaks

(From: Frank Fendley (frank.fendley@datacom.iglou.com)).

It sounds like the protection circuit (usually a relay) is cutting in during
louder music passages.  This is caused by an imbalance in the amplifier
circuitry, generally resulting in a DC offset voltage appearing on the output.
The usual cause is a defective transistor(s), probably in the earlier stages
in this case.

Of course, it could also be that you have 10 sets of speakers connected
to the amplifier and all the volume levels turned to the stops - it is
simply protecting itself from abuse! :-) --- sam.

  14.12) Speaker outputs do not come on or shut off immediately

(From: Ronald Dozier (dozier@strauss2.udel.edu)).

The protection relay usually detects DC offset at the speaker terminals
and then open's the speaker leads.  Check for a DC offset > 100 mV or so
before at the output, before the protection relays.

Leaky outputs are the first to suspect.

In most PP drivers the voltage between the bases of the output transistors
should be about 2 Vbe or around 1.2 volts.  0V is definitely a problem.  I
have only seen one amp (mine) that used 4 Vbe. or about 3.2 volts.
The voltage across the emitter resistors without a load are in the 0 to 20 mV
range.  This voltage should not increase appreciably over time and is set with
the bias adjustment.  Careless playing with the bias pot will result in output
transistor destruction.  It is best set with the aid of a distortion analyzer. 

All resistors/transistors in the driver and output stage and in some cases the
pre-amp are all suspect.  The small valued ones like to change value.
Compare with functioning channel.

  14.13) Dead channels on front-end audio components

Unlike big amplifiers, these are not normally failures caused by abuse or
high power components.  This type of equipment includes preamps, cassette
decks, CD players, tuners, etc.

First, eliminate the audio patch cables by trying a different set or swapping
left and right at both ends.  In addition, confirm that your amplifier is
operating on all cylinders (or channels).

Assuming this does not turn up anything:

For a tuner, the problem is almost certainly very near the output - probably
a bad connection, bad jack, or bad final IC or transistor stage.  There isn't
much between the demodulator and the line output.

For a tape deck, much more can be involved.  First, clean any mechanical
REC/PLAY mode and other switches with contact cleaner as dirty contacts
may result in one channel dropping out.  If this does not help, determine
if the output of the tape head is making it to the toutput by touching the
terminals on the playback head with a tiny screwdriver when in play mode -
you should get a hum when you are on the appropriate signal wire.  If there
is none for the bad channel, then you will have to either trace forward from
the head or backward from the output.  If you do hear a hum in the defective
channel, the tape head itself may be bad - shorted or open - very dirty.

Older tuners, receivers, premaps, tape decks, etc. used discrete transistors
and circuit tracing was possible.  Modern equipment relies on ICs but pinouts,
at least, are generally available by checking a cross reference guide such
as those put out by ECG, NTE, or SK.

Again, first eliminate bad jacks or cables -- and with tape decks - clean
the REC/PLAY (and other) mode selector switches.

  14.14) Equipment hums or buzzes

Assuming there are no other symptoms and the sound is coming from inside
the unit and not the loudspeakers, this is probably simply due to vibrating
laminations in the power transformer or motor(s) or nearby sheetmetal that
is affected by the magnetic fields from the power transformer or motor(s).
Most of the time, this is harmless but can definitely be quite annoying
especially when one expects total silence from their audio equipment.
If the noise is coming from any motors or their vicinity, refer to the
section: "Motor noise in audio equipment".

Sometimes, simply tightening the screws that hold the transformer or motor
together or the mounting screws will be all that is needed.  Placing a
toothpick or piece of plastic in a strategic location may help.  It is
also possible to coat the offending component with a varnish or sealer
suitable for electronic equipment but be careful not to use so much that
cooling is compromised or getting any in bearings or locations that would
interfere with rotating parts.

Dirty power - a light dimmer on the same circuit - may also result in increased
magnetic noise.  See the section: "Dirty power and buzz from equipment".

If the hum or buzz is in the audio, there could be a bad filter capacitor
in the power supply, other power supply problems, bad grounds inside the
unit or general ground problems with external equipment, or other bad
connections.  Disconnect all external devices (except the speakers if you
do not have a pair of headphones) and determine if the problem still exists.
Proceed accordingly.  Some Sony receivers are known to develop bad grounds
internally and just tightening the circuit board mounting screws and/or
resoldering ground connections will cure these.

Overloads can also cause a hum or buzz but would generally result in other
symptoms like a totally or partially dead amplifier, severe distortion, smoke,
six foot flames, etc.

If the problem is only annoying when the equipment is not in use, as a last
resort (where no memory or clock functions run off the AC line), putting in
an AC line switch may not be such a bad idea.

  14.15) Dirty power and buzz from equipment

Power line waveforms that are not sinusoidal can cause buzz.  Multiple
devices on the same circuit (or even different circuits) can interact.
A TV or other equipment may add to the problem since its switching power
supply draws current only on part of each cycle.

Excessive voltage can also increase the 'magnetic noise' from motors and
power transformers.  This sound is a result of core or winding vibrations.

You need to check for both of these possibilities - a calibrated scope is
best.  DMMs and VOMs may not read correctly with non-sinusoidal waveforms.

  14.16) Identifying and correcting sources of interference

Although this is a rather special application, similar problems and solutions
apply to other interference problems.  Also see the section: "Interference on AM radio band".

"I am using a 12V DC to 110 VAC converter in my car, to run a small TV/VCR.
 It works fine.  But the TV speaker is not very good.

 So I got one of those cassette adapters that has an audio cassette on one
 end, and a headphone jack on the other.  I plug that into the TV, and the
 cassette slot on my car stereo.  So then I can hear the TV sound on the
 car speakers, which are much better speakers.  

 But now there is a lot of high frequency noise that way, on the car speakers.
 It is very irritating.  A high frequency buzz of some kind.  How can I reduce
 or eliminate that noise?"

(From Duncan (duncan@punk.net)).

First we have to figure out where it is coming from.  The inverter is certainly
a noise source, and without spending a large sum for a well filtered inverter
you have to deal with the noise somehow.

One possibility is that the noise is on the 12 volt power supply going to your
car stereo.  To test for this, play a blank tape while running the TV and
listen for the same noise.  Fix with filters on the power leads of stereo
and/or inverter, wire to a solid clean rail very close to the battery.

Another possibility is capacitive coupling between the TV, connected to the
higher voltage side of your inverter, and the tape deck's playback heads.  This
might be alleviated by using a different, more isolated inverter or by using
another method of getting the audio into the stereo system.  FM modulators
intended for portable CD players might work.

Another possibility is that the power supply of the television is not rejecting
the higher frequency components of the inverter's signal.  The fix here would
be to add more capacitors and perhaps resistive or inductive filter elements
inside the television.  Check this by plugging headphones into the same jack
and listening for the noise.

Still another possibility is that the noise you hear is part of the horizontal
sync signal, which is not rejected well by all televisions.  This causes a high
pitched continuous squeal which is inaudible to some people.  The only easy
work-arounds here would be to try a different television or to turn down the
treble or select Dolby-B on your car stereo.  To test for this effect, try the
same hookup in your house with your home stereo, cassette deck, adaptor
cassette, and television.

Or just hook up your HiFi stereo VCR to the home stereo, move the whole mess
into the car, and ignore the car stereo.  Four of Radio Shack's little Pro-7
speakers with a Marantz 25 watt by four channel amplifier worked quite well
for me, especially when combined with a hand-held LCD monitor :-).

  14.17) Interference on AM radio band

This sort of problem is usually in the form of a buzz or hum at 60 Hz or 120
Hz (or 50 Hz or 100 Hz if your power is at 50 Hz).  There may be a little of
this on a small portion of the AM band but if it is excessive and interferes
with even strong stations, then a remedy is needed!  The following approach
should serve to locate the source if it isn't obvious:

(From: Doug (dslosty@pipeline.com)).

First, turn off the main house breakers and listen on AM with a battery
operated portable radio.

If the noise has disappeared, then you are generating the interference
in your own home and its time to check out things like light dimmers,
fluorescent lamps, touch-control incandescent lamps, motors, even cordless
phones, etc.

If the interference is still present on the portable AM radio, with the
breakers off, walk around the perimeter of the house and see if it's loudest
near the electric service entrance.

If it is, walk up and down the street and try to see if the intensity varies
(your neighbors will think you're weird - but what the heck!).

If the interference comes from outside of your home, it's time to call
the electric utility company and ask to speak with one of their
engineers.  The electric industry is required by the U.S. FCC. to
keep radio interference (RFI) to a minimum.  They may try to stonewall
you but if you persist, they will sent out an engineer with radio
direction finding equipment to locate the source of the interference.
If the source is a piece of equipment on a non-cooperative neighbor's
property, you may have another problem - but - one step at a time.

I've been through this procedure several times. Last time, the electric
company engineer tracked it to a broken and arching pole insulator.

As a former AM broadcast engineer (and current HAM radio operator),
I've experienced this problem enough to know that while challenging,
the interference source can always be found.

(From: Mr Fixit (mrfixit@cyberhighway.net)).

Radio Shack sells RF chokes. Label says "SNAP-ON FILTER CHOKES (2) cat. no.

They open up and snap together over your wires. Very simple to install and
come with comprehensive instructions.

With a little experimentation you can see if you need it on your power
cord, on the speaker wires or both. (these wires can act as antennas for
certain frequencies of RFI)

I use them all over my house on phones, TV's, stereos, computer speakers
etc to block out RFI from my CB base station and vis-versa.

BTW: if you happen to have any unneeded computer monitor cables laying
around, the oversize collar near the end is a RF choke. I had a couple so I
cut the covering and slid them off the cable. I put them onto our cordless
phone base unit antenna as an experiment to see if it would reduce the
ever-present buzz it had. To my surprise, the buzz disappeared with no loss
of signal strength.

(From: Dan Hicks (danhicks@millcomm.com)).

An even better idea is to put these chokes on the RF **generators** in 
your house.  I'm not sure if it's "code" to install them on permanent 
wiring, but it should be safe to do so so long as you are reasonably 
careful.  And it's easy to install them on any plug-in devices that appear
to cause problems.

  14.18) Internal fuse blew during lightning storm (or elephant hit power pole)

Power surges or nearby lightning strikes can destroy electronic equipment.
However, most of the time, damage is minimal or at least easily repaired.
With a direct hit, you may not recognize what is left of it!

Ideally, electronic equipment should be unplugged (both AC line and phone
line!) during electrical storms if possible.  Modern TVs, VCRs, microwave
ovens, and even stereo equipment is particularly susceptible to lightning and
surge damage because some parts of the circuitry are always alive and therefore
have a connection to the AC line.  Telephones, modems, and fax machine are
directly connected to the phone lines.  Better designs include filtering and
surge suppression components built in.  With a near-miss, the only thing that
may happen is for the internal fuse to blow or for the microcontroller to go
bonkers and just require power cycling.  There is no possible protection
against a direct strike.  However, devices with power switches that totally
break the line connection are more robust since it takes much more voltage
to jump the gap in the switch than to fry electronic parts.  Monitors and
TVs may also have their CRTs magnetized due to the electromagnetic fields
associated with a lightning strike - similar but on a smaller scale to
the EMP of a nuclear detonation.

Was the unit operating or on standby at the time?  If was switched
off using an actual power switch (not a logic pushbutton), then either
a component in front of the switch has blown, the surge was enough to
jump the gap between the switch contacts, or it was just a
coincidence (yeh, right).

If it was operating or on standby or has no actual power switch, then
a number of parts could be fried.

Many devices have their own internal surge protection devices like MOVs (Metal
Oxide Varistors) after the fuse.  So it is possible that all that is wrong is
that the line fuse has blown.  Remove the case (unplug it!) and start at
the line connector.  If you find a blown fuse, remove it and measure across
the in-board side of fuse holder and the other (should be the neutral) side
of the line.  With the power switch off, this reading should be very high.
With the switch on, it may be quite low if the unit uses a large power
transformer (a few ohms or less).  For example (assuming power transformer
operated supply):

        * Small AC adapter - 100 to 500 ohms.
        * Large AC adapter - 10 to 100 ohms.
        * VCR - 15 to 30 ohms.
        * Cassette deck or CD player - 25 to 100 ohms.
        * Stereo receiver or amplifier - .5 to 10 ohms.

Some may be outside these ranges but if the reading is extremely low, the
power transformer could have a partially or totally shorted primary.  If
it is very high (greater than 1 K ohms), then the primary of the power
transformer may be open or there may be blown thermal fuse under the outer
insulation wrappings of the transformer windings.  This may be replaceable.

If the unit has a switching power supply, see the document: "Notes on the
Troubleshooting and Repair of Small Switchmode Power Supplies".

If the resistance checks out, replace the fuse and try powering the unit.
There will be 3 possibilities:
1. It will work fine, problem solved.

2. It will immediately blow the fuse.  This means there is at least one
   component shorted - possibilities include an MOV, line filter capacitor,
   transformer primary.

3. It will not work properly or still appear dead.  This could mean there are
   blown fuses or fusable resistors or other defective parts in the power
   supply or other circuitry.  In this case further testing will be needed
   and at some point you may require the schematic.

  14.19) Use of surge suppressors and line filters

Should you always use a surge suppressor outlet strip or line circuit?
Sure, it shouldn't hurt.  Just don't depend on these to provide protection
under all circumstances.  Some are better than others and the marketing
blurb is at best of little help in making an informed selection.  Product
literature - unless it is backed up by testing from a reputable lab - is
usually pretty useless and often confusing.

Line filters can also be useful if power in you area is noisy or prone
to spikes or dips.

However, keep in mind that most well designed electronic equipment
already includes both surge suppressors like MOVs as well as L-C
line filters.  More is not necessarily better but may move the point
of failure to a readily accessible outlet strip rather than the innards
of your equipment if damage occurs.

It is still best to unplug everything if the air raid sirens go off or
you see an elephant wearing thick glasses running through the neighborhood
(or an impending lightning storm).

  14.20) Surge Suppressor/UPS cascading

(From: Fred Noble (f-noble@suttondesigns.com)).

A large number of users still seem confused about the use of a Surge
Suppressor in line with a UPS. The general rule is, do NOT plug a surge
suppressor INTO the OUTPUT of a UPS that produces a non-sinewave output that
exceeds 5% Total Harmonic Distortion (or THD) when the UPS operates from
battery supporting any load under any ambient conditions.  Do NOT plug a Line
Conditioner or other type of filter into the UPS either.

You can plug a UPS into a well grounded surge suppressor, but this is not
always a good idea, especially when we are talking about various 'low cost'
surge suppressors of questionable electrical integrity.  We constantly hear of
low-end surge suppressor recalls for safety reasons, with several recent
recalls ordered by the U.S. Consumer Product Safety Commission, for example, http://cpsc.gov/cpscpub/prerel/prhtml97/97078.html.  A cursory search using
the keywords 'surge arrester consumer recalls' with the Excite engine reveals
several such recalls.

If the surge suppressor you plug the UPS *into* is electrically 'safe' you are
still extending the ground path with such a cascading arrangement, which, on
balance, may not be wise. The UPS should provide Surge Suppression energy
ratings of 480 Joules or more.  Then, you probably wouldn't require the
additional upstream surge suppressor at all. This does not mean that you
shouldn't also have a surge suppressor installed at the MAINS or the branch
panel, however.  We are only talking about the extra, stand-alone, AC
protection devices.

This is also not to say that you should not provide additional surge
suppression for your modem or UTP connections!. This you must do, and a low
cost device that is also a *high quality* device, should be used.  These
devices are designed specifically for the protection of DC electrical surges
and they are not used in series with a UPS anyway.

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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]