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Bose powered acoustimass system, sucking current.
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FarberBear
Feb 18, 2000, 3:00:00 AM2/18/00
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This Bose system is a cd player/tuner matched with a powered subwoofer and
accompanying speakers. The problem is when the unit is switched to cd mode,
within a few seconds, and sometimes as soon as you press the "cd" button, the
powered subwoofer which is also the amplifier for the regular speakers starts
drawing in excess of 3 amps from the AC line. The ammeter on my bench supply
pulsates about twice a second. If I don't shut it down immediately, it will
blow the main fuse within a few seconds. The strange thing about this problem
is that this problem does not happen in tuner mode. If I unplug the power amp
portion of the system and listen to the cd player via the tape out jacks, it
sounds normal. There is no start up transient from the cd player that I can
detect from the audio line but that doesn't seem to be where the problem is
anyway. The way the powered speakers are hooked to the main unit is with a
special cable that includes a "stereo" system control plug, and a left and
right speaker wire. Even with the speaker wires disconnected and just the
control plug inserted, the system still pulsates. So that pretty much
eliminates any problems with the audio output circuits. The electronics
included in the audio amplifier looks more of car stereo quality. It is also
covered with a massive heat sink which makes trouble shooting pretty much
impossible. I suppose I could remove the heat sink and start checking voltages
but even if I had a schematic, that would be quite tedious. Turn it on, rush to
make a voltage measurement before the fuse blows. And then what? The fact that
it uses a control line to power up makes this complicated. Even if I were able
to lower the AC voltage to a non-destructive current level, I'm not sure I
could make any sense out of this situation. By the way, I did go over all the
connections and made sure the soldering was in good condition. I also made sure
that the power supply that houses the control unit, the cd player, and the
tuner was in good condition.
accompanying speakers. The problem is when the unit is switched to cd mode,
within a few seconds, and sometimes as soon as you press the "cd" button, the
powered subwoofer which is also the amplifier for the regular speakers starts
drawing in excess of 3 amps from the AC line. The ammeter on my bench supply
pulsates about twice a second. If I don't shut it down immediately, it will
blow the main fuse within a few seconds. The strange thing about this problem
is that this problem does not happen in tuner mode. If I unplug the power amp
portion of the system and listen to the cd player via the tape out jacks, it
sounds normal. There is no start up transient from the cd player that I can
detect from the audio line but that doesn't seem to be where the problem is
anyway. The way the powered speakers are hooked to the main unit is with a
special cable that includes a "stereo" system control plug, and a left and
right speaker wire. Even with the speaker wires disconnected and just the
control plug inserted, the system still pulsates. So that pretty much
eliminates any problems with the audio output circuits. The electronics
included in the audio amplifier looks more of car stereo quality. It is also
covered with a massive heat sink which makes trouble shooting pretty much
impossible. I suppose I could remove the heat sink and start checking voltages
but even if I had a schematic, that would be quite tedious. Turn it on, rush to
make a voltage measurement before the fuse blows. And then what? The fact that
it uses a control line to power up makes this complicated. Even if I were able
to lower the AC voltage to a non-destructive current level, I'm not sure I
could make any sense out of this situation. By the way, I did go over all the
connections and made sure the soldering was in good condition. I also made sure
that the power supply that houses the control unit, the cd player, and the
tuner was in good condition.
Any suggestions? Anyone ever work on this beast?
Thanks for your replies.
David Farber
David Farber's Service Center
L.A., CA
FarberBear
Mar 2, 2000, 3:00:00 AM3/2/00
to
Update on this repair:
I decided to try the Bose website for a contact number. They have an 800 number
listed so I tried that. The first time I called Bose customer service, I was on
hold for an hour and then got cut off. The second time I called, I was only on
hold for 30 minutes. Finally, a Bose customer service rep answered. In order to
talk to someone who actually knows the insides of this amp, you have to
persuade the customer service rep to let you talk to a techncian even though
you are not an authorized Bose dealer and don't have a schematic. I pleaded
with the customer service rep to just give me 5 minutes with a tech to ask my
question. He connected me to a tech's voice mail. Honestly, I didn't think I
would get a call back. When a tech did call me back the following day, he was
extremely helpful. He walked me through the troubleshooting steps. In about 15
minutes, we pinpointed the problem to a leaky smd transistor which is
responsible for switching the optocoulpler which in turn, controls the power
on/off via a triac.The reason the problem only occurred in cd mode had
something to do with the load on the 10V control line. When the unit is powered
up, 10 volts is applied to the power amp to electronically switch it on. Of
course the cd player put more load on this 10 volt supply than the tuner did
but I guess it was enough of a difference that the already leaking transistor
couldn't do its job. Once the transistor was replaced, the set worked like a
charm.
I decided to try the Bose website for a contact number. They have an 800 number
listed so I tried that. The first time I called Bose customer service, I was on
hold for an hour and then got cut off. The second time I called, I was only on
hold for 30 minutes. Finally, a Bose customer service rep answered. In order to
talk to someone who actually knows the insides of this amp, you have to
persuade the customer service rep to let you talk to a techncian even though
you are not an authorized Bose dealer and don't have a schematic. I pleaded
with the customer service rep to just give me 5 minutes with a tech to ask my
question. He connected me to a tech's voice mail. Honestly, I didn't think I
would get a call back. When a tech did call me back the following day, he was
extremely helpful. He walked me through the troubleshooting steps. In about 15
minutes, we pinpointed the problem to a leaky smd transistor which is
responsible for switching the optocoulpler which in turn, controls the power
on/off via a triac.The reason the problem only occurred in cd mode had
something to do with the load on the 10V control line. When the unit is powered
up, 10 volts is applied to the power amp to electronically switch it on. Of
course the cd player put more load on this 10 volt supply than the tuner did
but I guess it was enough of a difference that the already leaking transistor
couldn't do its job. Once the transistor was replaced, the set worked like a
charm.
I tip my hat to Paul Bedard of Bose Corp. who took the time to help me solve
this crazy problem. He then *called* me back later in the day to see if his
advice solved the problem. I hope the other manufacturers are taking notes here
on how to administer good service relations with small independent shops.
>Subject: Bose powered acoustimass system, sucking current.
>From: farbe...@aol.com (FarberBear)
>Date: 2/17/00 5:05 PM Pacific Standard Time
>Message-id: <20000217200509...@ng-ca1.aol.com>
Al, N2NKB
Mar 2, 2000, 3:00:00 AM3/2/00
to
Nice story. Hats off to Paul from Bose.
Al
Al
FarberBear wrote in message <20000302142637...@ng-de1.aol.com>...
William Muff
Sep 8, 2020, 8:04:31 PM9/8/20
to
David Farber
Sep 9, 2020, 12:48:03 AM9/9/20
to
As this interaction happened over 20 years ago, I only have a vague
recollection of this repair. Unfortunately, I am unable to answer your
question about the amperage of the 10v line.
Good luck.
--
David Farber
Los Osos, CA
David Farber
Sep 9, 2020, 12:48:46 AM9/9/20
to
On 9/8/2020 5:04 PM, William Muff wrote:
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