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My Home Cinema systems keep dieing


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Old 06-11-2006, 13:42
pmoule1
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I had a Sanyo Home Cinema system which stopped working in September. When I turned it on it booted up but then you could hear a mechnical switching noise and it cut out. As it was a few years old I got a new system a Denon DHT 500SD, but now after about 1 month of having it I've got pretty much the same fault; unit switches on but then there is a switching noise 'Protect' is shown on the display and it cuts out. This has now gone back for a repair which will take a few weeks.

My concern is something has caused the same fault, what is the problem, is it a protection circuit kicking in? If so what has caused it, could it be something to do with my power supply? It seems starange it is only affecting home cinema systems, are thse more sensitive to electrical surges?

My worry is that my new system will be fixed but then the fault will re-appear the day after the warranty expires.
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Old 06-11-2006, 14:44
Chris Simon
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Is ther any signal being fed into it at the time it cuts out?

I had a similar problem with my Denon amp. I had turned up the centre speaker level to the highest it would go and I think that was overloading it. Have you done anything similar? The way to sort this is to make sure the volume is down low and nothing is being fed into it when you switch on, then go through your individual speaker setups to see if anything is unusually high.

Also - have you got a line-level signal going into, say, a Phono (magnetic cartridge) input on the amp if it's got one?
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Old 06-11-2006, 14:56
pmoule1
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I had an optical input from my sky+ box and the scart out is connected to my Tv. Unit was cutting out even with sky+ and tv off and trying to listen to the tuner, it appeared pretty fatal.
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Old 06-11-2006, 16:08
TommyW
 
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Have you checked all speaker cables?

You only need one strand to touch a neighbouring connection and the unit will trip in to safe mode.
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Old 06-11-2006, 16:31
chrisjr
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Ditto TommyW.

What you describe in the OP sounds very much like the amp's protection circuit kicking in because of a fault in the speaker wiring. The noise you hear is most probably the relays on the output of the amp switching to disconnect the speakers before the amp fries itself. It is therefore quite likely that the amp is perfectly OK but that one or more speaker leads has a dodgy connection causing a short circuit.

So carefully inspect all the wiring for both stray strands of copper poking out of the terminal blocks and also any damage to the insulation of the leads which exposes the copper wire. Both can lead to short circuits. If you do it properly you should not see a single strand of copper anywhere, all bare wire should be fully hidden within the terminals.

NB this short circuit could be between speaker terminals or from a speaker terminal to the metalwork of the amplifier case

And take care "hoovering" round the speakers. It is quite easy to snag a speaker wire and tug it partially free of the terminal. Again this may release a strand of wire and that is all you need to cause a short circuit and activate the amps protection circuit.
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Old 08-11-2006, 13:04
pmoule1
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Disconnected speakers and cut-out still occurs just after switching on. It is very strange the same problem has occured on two different systems within a couple of months. Both have different speakers as well.
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Old 08-11-2006, 13:36
chrisjr
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Originally Posted by pmoule1
Disconnected speakers and cut-out still occurs just after switching on. It is very strange the same problem has occured on two different systems within a couple of months. Both have different speakers as well.
If the only thing connected to the amp is the mains lead and you have the volume control on it's minimum setting but the protection circuit still kicks in then there is definitely something amiss somewhere. I'm assuming here that when you say you disconnected the speakers you actually removed the wires from the amplifier terminals?

Is it actually cutting out or are you hearing the delayed speaker switch on operating? Or does it show PROTECT on the display till you turn the amp off?

I have a Denon amp which uses the protection relays to disconnect the speakers for a few seconds after switching on. You then hear a click as the relays change over and re-connect the speakers. Could this be what you are hearing? It would be strange indeed if the protection circuit activated even though nothing is connected to the amp.

First step, have a very careful look at the back of the amp around the speaker terminals. Make sure there are no strands of wire that could be short circuiting the speaker terminals. This is easy to do if the terminals are the screw type (where you screw down a plastic "knob" to clamp the wires). It is not unknown for a strand of wire to break off and wedge itself across two terminals or between a terminal and the chassis of the amp.

Undo all the speaker terminals fully and give the amp a gentle shake to dislodge any broken strands of wire. Or use a small paintbrush to wipe over and around the terminals which should pick up anything that shouldn't be there.
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Old 08-11-2006, 17:12
Richard46
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Originally Posted by chrisjr
It would be strange indeed if the protection circuit activated even though nothing is connected to the amp.
The auto protect was cutting in on one of my Yamaha Amps with nothing connected. Richer sounds took this as evidence of a fault and repaired it under guarantee.

Richard
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