Marantz SM-80 'scratching' noises - diyAudio
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Old 14th May 2007, 08:46 AM   #1
kaspro is offline kaspro  New Zealand
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Join Date: May 2007
Unhappy Marantz SM-80 'scratching' noises

Well, I think I overdone it with my 'speaker party' The SM-80 is responsible for the bass in my speakers, and it seemed to have got a little too hot for it's output.
The output as such is fine, but :
- it takes quite a time to come 'online'
- there are scratching noises, which become louder- not the whole time, but every now and then- and (as far as I can hear) only at the right channel

It looks like the small electronic board at the front has become too hot, at least as I can see from the underside of the board. I replaced all the capacitors there, with no luck. The soldering points of the main transistors on that board look worst, but it seems it's not that easy to find these. I also re-soldered the whole board, with still no luck.
Maybe I'm lucky again and someone knows this phenomenon...

Thanks a lot in advance,
Chris
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Old 14th May 2007, 11:27 AM   #2
jaycee is offline jaycee  United Kingdom
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Join Date: Apr 2004
Location: Norwich, UK
You've probably blown one or more output transistors. You need to check them, also check the DC offset at the output. Is there a protection relay? Does it take a while for that to click on?
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Old 15th May 2007, 09:27 AM   #3
kaspro is offline kaspro  New Zealand
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Join Date: May 2007
mmh, that wouldn't be nice
Yes, the protection turns off very late (being in IT that's what I meant with 'becoming online' )
can I test the transistors with a normal multimeter, too (transistor test, inductivity and capacity) or would I need a osci for that (which I don't have)?
what approximately should the DC offset be?
Sorry for the probably dumb questions, but apart from soldering and electronic basics I'm pretty hopeless in electronics...

Thanks in advance,
Chris
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