Cause of blown fuse.

S

Sjouke Burry

Guest
Today, somebody donated an Akay AA-MBL radio/amplifier to me.
Not operational, on investigation two blown 15 amp fuses, by
the look of it, in the power amplifier.
Fuses replaced by 2X 6 amp , and to my surprise, everything
started working.

Now fuses dont blow just to surprise you.

So, how did the former owner manage to blow both?
 
Now, fuses don't blow just to surprise you.
Click to expand...
No, they don't.

"Something" caused a momentary high current drain that popped the fuses,
which sacrificed their existance to save the equipment. What this
"something" was is not always obvious. It could have been due to cranking up
the volume and clipping the amp for an extended period. It could have been
due to brief high line voltage. It could have been due to kicking the power
cord, causing an intermittent connection at the wall socket or cable socket
on the amp. It could be due to thermal fatigue.

To answer the question you're /really/ asking, but didn't ask... It's quite
possible for fuses to blow without there actually being anything permanently
"wrong" with the amplifier. The probability that this amp is defective in a
way that will cause it to explode or burst into flames is small.
 
Sjouke Burry <burrynulnulfour@ppllaanneett.nnll> wrote in message
news:4c61e6ce$0$14123$703f8584@textnews.kpn.nl...
Today, somebody donated an Akay AA-MBL radio/amplifier to me.
Not operational, on investigation two blown 15 amp fuses, by
the look of it, in the power amplifier.
Fuses replaced by 2X 6 amp , and to my surprise, everything
started working.

Now fuses dont blow just to surprise you.

So, how did the former owner manage to blow both?
Click to expand...

Self-healed capacitor short?
 
On Aug 10, 4:54 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll>
wrote:
Today, somebody donated an Akay AA-MBL radio/amplifier to me.
Not operational, on investigation two blown 15 amp fuses, by
the look of it, in the power amplifier.
Fuses replaced by 2X 6 amp , and to my surprise, everything
started working.

Now fuses dont blow just to surprise you.

So, how did the former owner manage to blow both?
Click to expand...
Where in the circuit are the fuses? If they are line fuses, it is
pretty hard to develop enough current through the power transformer
[?] to blow 15A fuses. If there is an outlet for a phonograph after
the fuses, it could have been a short plugged into that.
I did have one set that the 'line' capacitor failed and it was blasted
to oblivon so the set worked fine with a new fuse. The only clue that
the cap had been there was a bit of blackening near the tie strip and
two short leads with nice copper balls on the ends. Someone must have
taken the bottom off and removed all the bits of plastic and paper
since there were none present.

Neil S.
 
nesesu wrote:
On Aug 10, 4:54 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll
wrote:
Today, somebody donated an Akay AA-MBL radio/amplifier to me.
Not operational, on investigation two blown 15 amp fuses, by
the look of it, in the power amplifier.
Fuses replaced by 2X 6 amp , and to my surprise, everything
started working.

Now fuses dont blow just to surprise you.

So, how did the former owner manage to blow both?

Where in the circuit are the fuses? If they are line fuses, it is
pretty hard to develop enough current through the power transformer
[?] to blow 15A fuses. If there is an outlet for a phonograph after
the fuses, it could have been a short plugged into that.
I did have one set that the 'line' capacitor failed and it was blasted
to oblivon so the set worked fine with a new fuse. The only clue that
the cap had been there was a bit of blackening near the tie strip and
two short leads with nice copper balls on the ends. Someone must have
taken the bottom off and removed all the bits of plastic and paper
since there were none present.

Neil S.
The fuses sat right in the centre of the power amplifier print.
Click to expand...
I wold guess protection of the output stage.
The mains fuse was oke.
The set is still playing as I type this.
 
The fuses sat right in the centre of the power amplifier
print. [???] I would guess protection of the output stage.
The mains fuse was OK. The set is still playing.
Click to expand...
Driving a low-impedance speaker at high volumes can cause this. (I had it
happen once.)

LET ME REPEAT, because no one seems to be paying attention. A fuse (or
fuses) can pop for no /obvious/ reason. It doesn't mean the amplifier is
defective, or that the fuses are likely to blow again. This sort of thing
happens every day, and is nothing to worry about. *

If it /keeps/ happening, /then/ you have to find out why. Otherwise, don't
worry about it.

The last time this happened to me was about nine months ago. I accidentally
knocked the power cord out of an amplifier's AC socket. In putting it back,
I didn't push the connector in quickly and firmly enough, and the amplifier
"chattered" on and off. The inductive kickback generated enough current to
blow the AC fuse. This was completely normal, one of the reasons electronic
equipment is fused.

* I once serviced a ReVox open-reel tape deck that kept blowing its fuse.
The fuse popped every three or four times the unit was turned on. I watched
the fuse during turn-on, and saw it flex as it heated up from the inrush
current. After a few flexes, it broke.

Though it appeared to be the correct fuse for this deck, I decided to
replace it with a slow-blow fuse of slightly higher capacity (about a half
ampere, IIRC). The customer was happy, and as far as I know, the deck didn't
explode and his house didn't burn down.
 
Sjouke Burry wrote:
Today, somebody donated an Akay AA-MBL radio/amplifier to me.
Not operational, on investigation two blown 15 amp fuses, by
the look of it, in the power amplifier.
Fuses replaced by 2X 6 amp , and to my surprise, everything
started working.

Now fuses dont blow just to surprise you.
Click to expand...

I blame the queer resistors. ;-)
 
On Wed, 11 Aug 2010 01:54:53 +0200, Sjouke Burry wrote:

Now fuses dont blow just to surprise you.

So, how did the former owner manage to blow both?
Click to expand...
I showed him how. Purse your lips...
--
I have multiple DUIS, beat my kids, paid $360K for a house worth $275K
got handed a divorce and a Restaining Order to keep away from all of
them. I'm 36, got a beer belly that looks like I'm pregnant 9 months.
Gawd, isn't life good!
 
Sjouke Burry wrote:

[snip]

The fuses sat right in the centre of the power amplifier print.
I wold guess protection of the output stage.
The mains fuse was oke.
The set is still playing as I type this.
Click to expand...
Speaker leads shorted once upon a time?

--
Paul Hovnanian paul@hovnanian.com
----------------------------------------------------------------------
Have gnu, will travel.
 
William Sommerwerck wrote:
The fuses sat right in the centre of the power amplifier
print. [???] I would guess protection of the output stage.
The mains fuse was OK. The set is still playing.

Driving a low-impedance speaker at high volumes can cause this. (I had it
happen once.)

LET ME REPEAT, because no one seems to be paying attention. A fuse (or
fuses) can pop for no /obvious/ reason. It doesn't mean the amplifier is
defective, or that the fuses are likely to blow again. This sort of thing
happens every day, and is nothing to worry about. *
Click to expand...
My brother-in-law had a problem with his stereo when he moved into a
'new' house. The place has 8 built-in speakers and he has a state of the
art surround sound power amp. But when he cranks the volume up, the amp
shuts down (solid state protection, no fuses were harmed).

So I did a bit of poking around. First thing, the speaker jack plate on
the wall had only two pairs of terminals. Left and right, we assumed.
Bad news, as it was probably wired with 4 speakers in parallel to each
side. Then I popped the wall plate off. All 8 speakers were wired to one
terminal pair. The right power amp was driving 8 paralleled speakers.
The left power amp drove nothing.

Fortunately, all of the speaker wiring came down behind the terminal
plate. And his amp has (more than) eight outputs. So now they all get
their own speaker.

--
Paul Hovnanian mailto:paul@Hovnanian.com
------------------------------------------------------------------
f u cn rd ths u r usng unx
 
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