Mcintosh Amp Blown Fuse? - AVS Forum
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post #1 of 9 Old 03-20-2011, 06:43 PM - Thread Starter
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Hey everybody,

I just purchased a secondhand Mcintosh MC300, which worked perfectly when I first set it up last week, with the exception of the meter lamps. I disassembled my system to pull the light boards out to take to the dealer, but when I put the light boards back in and plugged in my receiver (which I'm using as a pre pro), I somehow blew the fuse in the Mcintosh.

The amp takes a 10 amp fuse, but the only thing I could find on Sunday that fit was a 5 amp fuse, which the amplifier promptly blew as soon as I turned it on (lights/power guard turned on momentarily, then went dark). Was that supposed to happen? If I get a proper 10 amp fuse, will the amplifier work?

Thanks in advance!
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post #2 of 9 Old 03-20-2011, 08:28 PM
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99% chance if it needs a 10 amp and you put a 5 amp it would blow. Get the right fuse and make sure it is of the same type. There is blow "slow-blow" and fast-blow. It should say that on the old fuse or somewhere around it. Usually it is fast blow but not always.

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post #3 of 9 Old 03-20-2011, 08:29 PM
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Now, if you put the 10 amp and it still blows, then you may have damaged something. Let us know how it goes with the 10 amp fuse and we can then think of the next step.

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post #4 of 9 Old 03-20-2011, 08:45 PM - Thread Starter
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Thanks amirm. I would've thought that the 5 amp fuse would hold, at least if I wasn't running anything through the amp at the time? I was only hoping the 5 amp fuse would confirm that there was nothing else wrong and I would replace it later in the week...

Do I have to go to my home audio dealer to get a 10 amp fuse? Radio Shack, Lowes, Home Depot, auto supply shops... The best they had was 5 amps in the size the Mcintosh needed.
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post #5 of 9 Old 03-20-2011, 09:07 PM
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There is a start-up surge current that can cause it to blow. And at any rate, you want to rule that issue out.

What size is it? Radioshak has 10 amp normal size: http://www.radioshack.com/product/in...ductId=2103757

Do you have Fry's next to you? They should have it.

If not, there are lots of online sources. Here is one: http://www.mouser.com/Circuit-Protec...p+fuse&FS=True

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post #6 of 9 Old 03-20-2011, 09:15 PM - Thread Starter
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The old fuse was one size smaller than that, a 5 x 20mm fuse. I'll check with the local Mcintosh dealer first, I figure they might have a few lying around in case their demo systems have issues.

Thanks for your help, hope to update tomorrow.
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post #7 of 9 Old 03-25-2011, 06:15 AM - Thread Starter
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So my 10 amp fast blow fuses arrived, and the amp is still blowing through them. Should I have gotten the slow blow fuses instead? I might just give up and take the amp to the dealer at this point unless someone has any other ideas!

Thanks!
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post #8 of 9 Old 03-25-2011, 08:33 AM
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Quote:
Originally Posted by aliasfox View Post

So my 10 amp fast blow fuses arrived, and the amp is still blowing through them. Should I have gotten the slow blow fuses instead? I might just give up and take the amp to the dealer at this point unless someone has any other ideas!

Thanks!

If it is the same type as the original, then no, you did the right thing and putting slow-blow would risk fire and further damage to the equipment. If the fuse is not the right type, yes, it would blow even if everything is working as the initial current surge zaps it. So double check that but after that, you need to take it to the dealer.

Oh, one more thing. Reading your original post, I would back out the fix you made to be sure that is not causing it. Disconnect the meter board or the light and see if it still does it.

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post #9 of 9 Old 03-25-2011, 02:20 PM - Thread Starter
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The markings aren't identical, so I'm thinking the old one might've been slow blow, but like you I can't imagine that really being the issue.

I've tried it with the light meters connected and disconnected, so now I have two blown 10 amp fuses. The receiver hasn't been connected, nor have the speakers.

I'll bring it in on Monday... Hopefully th repair isn't too painful...
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