Boston Acoustics CR400 Subwoofer / Fuse Blower

P

pc_whocares

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A friend of mine brought me a BA CR400 subwoofer that's blowing
fuses. I told him I'd have a look because that sort of failure will
usually produce brown or cooked components on a PC board, making it
easy to fix.

After cracking the case, there is nothing obviously wrong with any of
the components.

The unit has some interesting features where it will automatically
turn on and off under certain circumstances, so, even when the power
switch is OFF, when it is plugged in the speaker hums a nice 60 Hz
sound for a second or two, and the 1 amp slo blow fuse goes.

It's about ten years old. I'm thinking power supply capacitor --
there are two. I'll try BA on Tuesday to see if they have any inputs.

In the interim.. Suggestions?

tanks

pc
 
"pc_whocares" <pc_whocares@yahoo.com> wrote in message
news:08c7d7a2-39ff-4da6-b2a4-65e9a743aa4d@w31g2000prd.googlegroups.com...
A friend of mine brought me a BA CR400 subwoofer that's blowing
fuses. I told him I'd have a look because that sort of failure will
usually produce brown or cooked components on a PC board, making it
easy to fix.

After cracking the case, there is nothing obviously wrong with any of
the components.

The unit has some interesting features where it will automatically
turn on and off under certain circumstances, so, even when the power
switch is OFF, when it is plugged in the speaker hums a nice 60 Hz
sound for a second or two, and the 1 amp slo blow fuse goes.

It's about ten years old. I'm thinking power supply capacitor --
there are two. I'll try BA on Tuesday to see if they have any inputs.

In the interim.. Suggestions?

tanks

pc
Click to expand...

Chances are that one or more of the output transistors are shorted, and if
the unit has a relay that switches power to the power amp, its contacts are
likely welded shut. I've repaired a fair number of subwoofer amps, and this
is the most common problem that I've seen.
You'll be ahead of the game if you unsolder the output transistors, check
them for shorts and go from there. If you find that one of the transistors
is shorted, be sure to replace them in pairs. A subwoofer usually doesn't
need matched pairs, but some models might. Also, if you find shorted or
open transistors in the output, be sure to check the transistors that drive
the outputs. They could easily be damaged as well.

Cheers
--
Dave M
masondg44 at comcast dot net

One good thing about Alzheimer's; you get to meet new people every day.
 
pc_whocares wrote:

A friend of mine brought me a BA CR400 subwoofer that's blowing
fuses. I told him I'd have a look because that sort of failure will
usually produce brown or cooked components on a PC board, making it
easy to fix.

After cracking the case, there is nothing obviously wrong with any of
the components.

The unit has some interesting features where it will automatically
turn on and off under certain circumstances, so, even when the power
switch is OFF, when it is plugged in the speaker hums a nice 60 Hz
sound for a second or two, and the 1 amp slo blow fuse goes.
Click to expand...
If it hums like that, I would suspect the power supply rectifier(s).
It's about ten years old. I'm thinking power supply capacitor --
there are two. I'll try BA on Tuesday to see if they have any inputs.

In the interim.. Suggestions?

tanks

pc
Click to expand...

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.
 
"CJT" <abujlehc@prodigy.net> wrote in message
news:4A19FF87.9030907@prodigy.net...
pc_whocares wrote:

A friend of mine brought me a BA CR400 subwoofer that's blowing
fuses. I told him I'd have a look because that sort of failure will
usually produce brown or cooked components on a PC board, making it
easy to fix.

After cracking the case, there is nothing obviously wrong with any of
the components.

The unit has some interesting features where it will automatically
turn on and off under certain circumstances, so, even when the power
switch is OFF, when it is plugged in the speaker hums a nice 60 Hz
sound for a second or two, and the 1 amp slo blow fuse goes.

If it hums like that, I would suspect the power supply rectifier(s).

It's about ten years old. I'm thinking power supply capacitor --
there are two. I'll try BA on Tuesday to see if they have any inputs.

In the interim.. Suggestions?

tanks

pc


--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.
Click to expand...

Hum caused by the power supply cap(s) would not blow the fuse. A cap would
just be open circuit and the resulting ripple would cause the noise, but as
I say, the fuse would not blow. There's a short somewhere (main amp,
likely), but I think if a main cap were shorted, you'd never hear the hum
before the fuse blew.

Mark Z.
 
On Sun, 24 May 2009 21:16:39 -0500, CJT <abujlehc@prodigy.net> wrote:

pc_whocares wrote:

The unit has some interesting features where it will automatically
turn on and off under certain circumstances, so, even when the power
switch is OFF, when it is plugged in the speaker hums a nice 60 Hz
sound for a second or two, and the 1 amp slo blow fuse goes.

If it hums like that, I would suspect the power supply rectifier(s).
Click to expand...
I agree - if it /is/ 60Hz then half a bridge has disappeared...

--
Geo
 
Geo wrote:
On Sun, 24 May 2009 21:16:39 -0500, CJT <abujlehc@prodigy.net> wrote:


pc_whocares wrote:


The unit has some interesting features where it will automatically
turn on and off under certain circumstances, so, even when the power
switch is OFF, when it is plugged in the speaker hums a nice 60 Hz
sound for a second or two, and the 1 amp slo blow fuse goes.

If it hums like that, I would suspect the power supply rectifier(s).


I agree - if it /is/ 60Hz then half a bridge has disappeared...
Click to expand...
.... or shorted.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.
 
On May 24, 6:06 pm, pc_whocares <pc_whoca...@yahoo.com> wrote:
A friend of mine brought me a BACR400subwoofer that's blowing
fuses.  I told him I'd have a look because that sort of failure will
usually produce brown or cooked components on a PC board, making it
easy to fix.

After cracking the case, there is nothing obviously wrong with any of
the components.

The unit has some interesting features where it will automatically
turn on and off under certain circumstances, so, even when the power
switch is OFF, when it is plugged in  the speaker hums a nice 60 Hz
sound for a second or two, and the 1 amp slo blow fuse goes.

It's about ten years old.  I'm thinking power supply capacitor --
there are two.  I'll try BA on Tuesday to see if they have any inputs.

In the interim.. Suggestions?

tanks

pc
Click to expand...
Good advice from all of you.

I would expect that if a cap were bad but not shorted, it would not
necesessarily blow the fuse right away.. but who knows?

Rectifiers are easy to check, and that certainly makes sense.

I'll keep 'yall posted.

tanksAbunch

pc
 
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