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Old 18th October 2007, 05:20 PM   #1
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Question Help. What wrong with my amp? Technics SU-V98

I just wanted to play some fun to feed an audio signal from my digital multimeter into the amp. The signal is to be only frequency 30 to 40 Hz square wave and about 2V peak as per it's manual.
When I first connected, I could heard a low frequency from my speaker. BUT not within a second, the amp went dead.
I switched on & off the amp but still could not reset it.
In normal situation, I could heard a "click" sound from the relay, after switch on the power. But now there was no sound heard.
Is it the fault of the relay? Or some other components caused the malfunction?
Why just fed a low freq signal, the amp should able to handle it, could caused damage?
Hope that someone could give me guidance to repair it and make it back to function.
Thanks very much for the assistance in advance.

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Old 18th October 2007, 09:01 PM   #2
jaycee is offline jaycee  United Kingdom
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If the relay isn't clicking, this suggests one of two things:

1) there is a DC Offset problem at the output stage of the power amplifier, and the protection circuit has kicked in

2) The protection/startup delay circuit is damaged.

What you need to do here, is open her up and measure DC offset at the power amplifiers output, before the relay, using a voltmeter. If there is any large voltage present there, then that is the problem.

If not, then the protection circuit could be faulty.
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Old 18th October 2007, 09:20 PM   #3
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Did you have a load on the amp when doing the tests? Have you tried unplugging the amp from the wall and leaving it overnight?
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Old 19th October 2007, 04:24 AM   #4
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U blew it.
No amp can stand a square wave.
The forum will help u fix it.

Gajanan Phadte
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Old 19th October 2007, 05:09 AM   #5
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Dear Jaycee,
Thanks for the valuable instruction. I will test the voltage according to your method.
The relay circuit is very simply, only seen one transistor and 1 cap etc. If it was damage, I hope would be easy to replace them.


Dear richie00boy,
Surely I will try your method first as this was the easiest way to do.
Hope it work.


Dear gmphadte,
Thanks for your comments.
But I had separately tested the amp's pre-out and it had signal output. Therefore I could determined that's the problem at the amplifier stage.
BTW, any forum recommended are specialize in amp repair? Please kindly inform.


Thanks again for all of yours kind assistance.
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Old 19th October 2007, 06:45 AM   #6
jaycee is offline jaycee  United Kingdom
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Quote:
Originally posted by gmphadte
U blew it.
No amp can stand a square wave.
The forum will help u fix it.

Gajanan Phadte
This isn't true - plenty of amps will stand a square wave over a short time period into resistive loads (ie, for testing - the only time you really want to do this)

Also the wave wont really be square - it will be rounded somewhat by the action of the input filter stage.
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