Salvaging Logitech speaker system

[Mike S.]

I have a dead Logitech Z-680 5.1 computer speaker system that I was
wondering about doing salvage work on, before discarding.

It consists of a subwoofer with all the amp circuitry and connectors for
the main speakers on the back, and a dedicated control pod that connects
to it using a custom wired DB9 connector.

The system stopped working and, since it was under warranty (and
discontinued), Logitech simply replaced the entire thing with the current
model (Z-5500) and does not want any of the old equipment returned. The
old and new systems are electrically incompatible, so I just boxed the
Z-680 setup and am triyng to decide what to do with it.

The electronics pod, which contains the controls, analog/digital inputs,
Dolby/dts decoders, and preamp, powers up and detects and processes input
signals appropriately. There is a power-on "thump" in all speakers when
you fire the thing up, and the sobwoofer still has a little buzz coming
out of it (that was normal), but after that ... nothing. Audio goes in,
but not out. There is a special test mode that sends tones to all speakers
for setting levels ... I hear nothing.

I'm not sure if the failure is in the pod or the main (audio) unit on the
subwoofer, though I suspect the former. I opened the pod ... lots of
surface mount chips, no visible fuses or resettable devices. Not
user-serviceable.

The subwoofer has this huge metal cage bolted on the back which contains
the audio amplifier circuits. I'm pretty sure the DB9 input on the back
contains the 6-channel preamp output from the control pod. I was thinking
of trying to send some test signals into the subwoofer's input socket, 2
pins at a time, until I figure out whether any of them elicit audio output
from the speakers. Perhaps I can salvage the subwoofer and simply hook a
line-level audio cable to whichever of the two DB-9 pins gives the desired
effect.

Comments/suggestions? Thanks.

 

[James Sweet]

I have a dead Logitech Z-680 5.1 computer speaker system that I was
wondering about doing salvage work on, before discarding.

It consists of a subwoofer with all the amp circuitry and connectors for
the main speakers on the back, and a dedicated control pod that connects
to it using a custom wired DB9 connector.

The system stopped working and, since it was under warranty (and
discontinued), Logitech simply replaced the entire thing with the current
model (Z-5500) and does not want any of the old equipment returned. The
old and new systems are electrically incompatible, so I just boxed the
Z-680 setup and am triyng to decide what to do with it.

The electronics pod, which contains the controls, analog/digital inputs,
Dolby/dts decoders, and preamp, powers up and detects and processes input
signals appropriately. There is a power-on "thump" in all speakers when
you fire the thing up, and the sobwoofer still has a little buzz coming
out of it (that was normal), but after that ... nothing. Audio goes in,
but not out. There is a special test mode that sends tones to all speakers
for setting levels ... I hear nothing.

I'm not sure if the failure is in the pod or the main (audio) unit on the
subwoofer, though I suspect the former. I opened the pod ... lots of
surface mount chips, no visible fuses or resettable devices. Not
user-serviceable.

The subwoofer has this huge metal cage bolted on the back which contains
the audio amplifier circuits. I'm pretty sure the DB9 input on the back
contains the 6-channel preamp output from the control pod. I was thinking
of trying to send some test signals into the subwoofer's input socket, 2
pins at a time, until I figure out whether any of them elicit audio output
from the speakers. Perhaps I can salvage the subwoofer and simply hook a
line-level audio cable to whichever of the two DB-9 pins gives the desired
effect.

Comments/suggestions? Thanks.

I suspect the problem is something simple, cracked solder joint at a
connector, this might be a good opportunity to practice repair as a speaker
system is relatively simple and safe to work on.

 

[mike]

I have a dead Logitech Z-680 5.1 computer speaker system that I was
wondering about doing salvage work on, before discarding.

It consists of a subwoofer with all the amp circuitry and connectors for
the main speakers on the back, and a dedicated control pod that connects
to it using a custom wired DB9 connector.

The system stopped working and, since it was under warranty (and
discontinued), Logitech simply replaced the entire thing with the current
model (Z-5500) and does not want any of the old equipment returned. The
old and new systems are electrically incompatible, so I just boxed the
Z-680 setup and am triyng to decide what to do with it.

The electronics pod, which contains the controls, analog/digital inputs,
Dolby/dts decoders, and preamp, powers up and detects and processes input
signals appropriately. There is a power-on "thump" in all speakers when
you fire the thing up, and the sobwoofer still has a little buzz coming
out of it (that was normal), but after that ... nothing. Audio goes in,
but not out. There is a special test mode that sends tones to all speakers
for setting levels ... I hear nothing.

I'm not sure if the failure is in the pod or the main (audio) unit on the
subwoofer, though I suspect the former. I opened the pod ... lots of
surface mount chips, no visible fuses or resettable devices. Not
user-serviceable.

The subwoofer has this huge metal cage bolted on the back which contains
the audio amplifier circuits. I'm pretty sure the DB9 input on the back
contains the 6-channel preamp output from the control pod. I was thinking
of trying to send some test signals into the subwoofer's input socket, 2
pins at a time, until I figure out whether any of them elicit audio output
from the speakers. Perhaps I can salvage the subwoofer and simply hook a
line-level audio cable to whichever of the two DB-9 pins gives the desired
effect.

Comments/suggestions? Thanks.

Most of the busted speakers I've seen had mechanical problems.
Banged the volume control and broke it.
Banged the signal conector and broke it.
Dropped and cracked the circuit board.
You need either an oscilloscope or a signal injector.
mike

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[James Sweet]

Most of the busted speakers I've seen had mechanical problems.
Banged the volume control and broke it.
Banged the signal conector and broke it.
Dropped and cracked the circuit board.
You need either an oscilloscope or a signal injector.
mike

I don't think I've ever used either to repair speakers, usually the problem
is pretty apparent once you get it apart. A walkman is useful for supplying
a signal though, a DMM is usually sufficient for tracing.

 

[Mike Berger]

A Walkman makes a fine audio signal injector, but it's pretty
delicate and expensive,and has limited output.

 

[jakdedert]

I don't think I've ever used either to repair speakers, usually the problem
is pretty apparent once you get it apart. A walkman is useful for supplying
a signal though, a DMM is usually sufficient for tracing.

A *finger* is often enough to supply signal (although the walkman is
higher-level, more stable approach). Touch an input and listen for hum.
Another (working) powered speaker is useful as a signal tracer
(protect the input with a small capacitor).

A DMM 'good enough' for the above can be had for $10 or less, and will
come in handy in many other situations.

jak

 

[jakdedert]

A Walkman makes a fine audio signal injector, but it's pretty
delicate and expensive,and has limited output.

If you're testing *unpowered* speakers, yes. Otherwise, the output is
entirely adequate. Shuffle down to your local pawn shop or even thrift
store, and pick up a walkman for less than $5...not expensive at
all...or particularly delicate for that matter.

But if you're concerned re: the above, buy a signal generator (not less
expensive)...or a $1 (Dollar Tree store stock) FM radio.

jak

 

[Mike S.]

A *finger* is often enough to supply signal (although the walkman is
higher-level, more stable approach). Touch an input and listen for hum.
Another (working) powered speaker is useful as a signal tracer
(protect the input with a small capacitor).

A DMM 'good enough' for the above can be had for $10 or less, and will
come in handy in many other situations.

Thanks, I think that might be the safest initial move. Remembering that
one of the pins also supplies POWER to the control pod, I figured I'd test
things out with a DMM first, and cross off any pins that have voltage
coming out of them.

I've looked around and Logitech seems to have refused previous requests
for pinouts of the input connector; though some have disassembled the
subwoofer to fix internal rattles, nobody has bothered to map the input
port. Opening this thing is such a bear that, given the choice, I'd throw
it out rather than invest that much time if poking around from the outside
doesn't yield anything.

Thanks for the ideas, folks.