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Old 5th March 2004, 04:49 PM   #1
Fraser is offline Fraser  Abu Dhabi
diyAudio Member
Join Date: Mar 2004
Location: london
Default Hopefully a fairly easy problem for you lot!

One of the channels has blownon my Arcam alpha 5+ amplifier, I've swapped over the speakers and have replaced the fuse plus checked it's nothing stupid like the balance and still no joy. If I replace the fuse it blows in about a second.

I looked at the biwireable speaker cable and it had sheared causing the left and right wires to connect on the channel that has blown.

Is there a standard component that is the usual culprit in these cases? Arcam say it's probably a fusible resistors but how do I know what one looks like and how do I test if it's blown?!

I really don't want to replace it as the sound quality is still fantastic!

Any help would be well appreciated
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Old 6th March 2004, 05:26 PM   #2
diyAudio Member
Join Date: Dec 2003
Location: Munich
Hi Fraser!
....sounds serious!
You say the fuse blows within 1 sec.: Which fuse?
Is the fuse in line with the speaker and do you hear a heavy
thumbing of the woofer?
Is it the fuse of the powersupply and you hear nothing on the
speaker at all?

In case a)
you have a 50/50 chance that only a fuseable resitor (may be in
one of the DC-rails) has also blown and due to the missing supply the amp is giving DC and blows the fuse which is in series with the speaker.
But normally the protection circuit should should keep the speakers
turned off and you might hear nothing and in this case also a fuse
in series to the speaker would not blow. So unfortunately
case b) is more probable.

case b)

If the speaker protection circuit works well your speaker will
not be connected to the amp.
If in this condition the fuse in the supply blows, then this indicates
some or all output transistors are blown. They might also have taken some parts of the driver stage....
Without detailed knowledge about this you might get into real
trouble. Because you need to figure out all defect components
and replace them.....

A first step. If you measure the output transistors: Do some of them show a zero (or close to that) resistance?
If yes, you can try the following.
Replace the output transistors and hope everything is fine then (don't forget to readjust the idle current).
If the thing is not working then, you will need to learn the details
about your amp, or give it to the service, or you might have a friend who knows well about amps....

Wishing the best
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