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Old 29th June 2015, 01:56 PM   #1
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Default Sansui AU-4900 problem

Hi everyone.
I have a Sansui AU-4900 that I am having trouble with. Well... kind of..

See, outside the transformer there are 3 fuses. The one at the bottom (125V 6A) blows immediately every time. But the amp still seems to work great. All features appear to be working. I even had a microphone plugged in to try.

I have the schematic and circled where the fuse is. Does anybody have any ideas what the fuse is for?

Thanks for any help!
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Old 29th June 2015, 03:39 PM   #2
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Hard to tell where your circle is. Is it one of the yellow high lights? There are no fuses of that value listed in the schematic.
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Old 29th June 2015, 03:57 PM   #3
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Hi.. sorry, the fuse is where I highlighted it and underlined in red. the other two highlights are where the other two fuses are..
Yes the fuses are not shown on the schematic. And other amps of this model online just have and empty area where these fuses are.

I'm wondering if that fuse is used when this is plugged into another countries outlet of 240V. It would be drawing less amperage at a higher voltage? Just a thought
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Old 29th June 2015, 04:03 PM   #4
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I guess I say "other countries" and I should say non- Canadian. haha/.. We have 120 volts here. The amps I see online of this model seem to be from Australia and GB. They don't have the fuse. So perhaps that is the difference.
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Old 30th June 2015, 05:25 AM   #5
roger2 is offline roger2  United States
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You may get more replies if you increase the size of your schematic. Or enlarge the relevant section and post again. I am not able to read the schematic in your OP
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Old 30th June 2015, 05:34 AM   #6
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I blew twice the power transistors of my marantz 1122DC because the fuse for 110 V wasn't changed to 220V ( halved )
But...what a sound


BTW now I have a sansui au 5500...but this 4900 appeals me more
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Old 30th June 2015, 05:47 AM   #7
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I think I found the issue. A shorted diode.
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Old 30th June 2015, 06:51 AM   #8
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Yes, your fuse connected one of the two secondaries to the rectifier bridge.
Your amp was working without the fuse, but with half rectification.
Change the rectifier and the fuse and you're good to go
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