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Oops amplifier explosion

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Johnno2's picture
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Joined: 2 Feb 2009
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Not mine, thank goodness pray ,  My friend has reconnected his speakers after moving house, not realising some of the fine strands of the speaker cable were touching on the + and -  on the speakers posts, He said the music played ok for a couple of seconds then it tripped off,  He turned  it offf straight away, checked the conection which were now ok , He then went to turn the amp back on and he said there was a loud  bang with a bright flash from inside the unit Shock .  I have been to look at it and it lights up but with the LED flahing and a strange noise. There is no output.   I am not an electrician but I would have though the protection circuit would have activated,    Now he is bothered that anything connected, such as the  CD player could have had a surge going through via the inputs to affect it,    or that something on the speakers is damaged, could this be possible from a blown output stage on the amp, I would have thought not with anything connected to the inputs , but not so sure about the speakers, Before gets his amp repaired, it means me lugging mine round to see if the speakers and CD sound OK, Surley if the amp to speaker cable short circuits and blows the output tansistors nothing would go through the speakers to damage them puzzled

And what about any surges to components connected on the inputs

Any electronic/electricians out there

 

Inter_Voice's picture
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RE: Oops amplifier explosion

If you heard a big bang and saw sparks I would have though that one of the capacitors has exploded.  Open up the case and look for a damaged cap.

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Johnno2's picture
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RE: Oops amplifier explosion

Inter_Voice wrote:

If you heard a big bang and saw sparks I would have though that one of the capacitors has exploded.  Open up the case and look for a damaged cap.

We opened it but could see no obvious scorched components, but he does assure me it went with a loud pop, flash and a smell of solder , He is worried that  things connected to it might be affected by faults now due to any surges, but I told him that should not be the case as the power amp cant send surges of voltage and current back to the premp and inputs (can it) , I am no expert, and the speakers should not be affected, The amp is Marantz PM7000

up the music's picture
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RE: Oops amplifier explosion

To save you dragging your amp round you can test the speakers by connecting a battery across the speaker cable. You should get a click rather than a continuous tone. The bass/mid should be easily audible but you might need to have your ear pretty close to the tweeter to hear that.

I'm no sparky but damaging an output stage sounds pretty likely but do check for fuses as they're replaceable by the non technical. I can't imagine source components being damaged.

Hope it wasn't a nice amp.

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nopiano's picture
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RE: Oops amplifier explosion

Going back a few years I saw lots of amps go pop (I used to work in a shop that sold British hifi) often caused by setup errors, sometimes self destructing.

I never saw any connected items suffer.  This seems very unlikely.

Unless a very loud noise came from the speakers, they'll probably be fine too.  As suggested, if they 'pop' lightly when connected accross an AA battery that suggests they are still functioning (but it won't detect overheated voicecoils that scrape, though that's unlikely here).

I'm 99% sure it'll just be his amp that has expired.  

Hopefully it won't cost too much to fix.  I see one sold for £135 on eBay recently.

 

 

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dumbledore's picture
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Joined: 29 Dec 2012
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RE: Oops amplifier explosion

Don't reconnect the speakers to any amp unless you check them with an ohm meter. They should not show any DC resistance less then 3 ohms if they are rated at 4 ohms and 6 ohms if they are rated at 8 ohms. As for the amp shorting the output stage could have damaged the output stage if the protection circuit did not work. So when you reconnect the amp after the short the output stage stay shorted and starting burning things in the amp. I would look for exploded output transistors and power resistors in the output stage. They should be visible including burned out PCB in the area that can also be smelled.