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Old 5th March 2004, 04:47 PM   #1
Fraser is offline Fraser  Abu Dhabi
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Join Date: Mar 2004
Location: london
Default I think/hope this will be a simple 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 5th March 2004, 11:54 PM   #2
mwh-eng is offline mwh-eng  United States
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Join Date: Feb 2004
Location: Livingston, Montana
Don't know anything about your amp, but it sounds like the power transistor(s) has/have failed shorted. If a fusible resistor was blown, I wouldn't think the other fuse would blow. If the speaker wire on this channel was shorted and the amp does not have short circuit protection, you likely have blown output power transistors on this channel. My best quess without a schematic and more information.
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Old 6th March 2004, 12:46 AM   #3
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK
I agree.

A fusable resistor failing prevents the problem, it can't maintain it.

The simple answer is probably this :

One or more of the output devices on the shorted channel has
gone west, though it cannot be discounted that it has caused
further device failure in that channel.

1) remove output devices in failed channel, if fuse still blows
then your power supply has failed, refer to a skilled technician.
fuse ok ? then :

2) remove output devices from working channel and install in
the failed channel, if fuse blows then you have further device
failure in the failed channel, refer to a skilled technician.
fuse ok ? failed channel works ? then :

3) At this point you can replace both devices from the
failed channel and install into the other channel.

4) or swap them one one at a time into the working channel, to
ascertain the failed output device, (by the fuse blowing) at the
slight risk of causing the other device to fail.

Replace failed device and install the devices into both channels.

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Old 6th March 2004, 09:13 AM   #4
lucpes is offline lucpes  Romania
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Join Date: Dec 2003
Location: Romania, EU
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I'd do a good reading first to decide if you're up to the job. If you're in a hurry just get a schematic and get someone qualified. One piece of advice: do not connect the speakers until you have everything sorted out with the amp, you may blow the woofers if you do so!

Testing transistors in circuit:


Power amplifier repair tips:


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