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I'm very sad.
The little SAE amp I received this morning is already dead.
When I received it, i plugged it in the system, connected the preamp and speakers, then plugged the mains in.
Besides audible transformer "buzz" coming from the amp (not from the speakers) it worked very well for about 30minutes. The sound was amazing, better than what I expected.
Then bam, nothing... it cut... I checked the fuse, it was blown. Checked the service manual, the normal value for the fuse should be 1,25A for the export version (220V, the one I have) and 2,5A for the 110V version.
The burnt fuse was 2A :(
went to buy new fuses, put the new fuse in place, reconnected the amp to the mains, nothing, the fuse instantly burns, the amp doesnt even power up.
I suspect few things, all very bad news:
a)the amp couldn't stand the transport, the packing wasnt good enough, somehow it destroyed the transformer
b)the previous owner knew there was a problem with the amp and put a higher amperage fuse so that teh amp would work for a short while before dying;
c)the previous owned isn't responsible BUT because the fuse was the wrong value there's now more damage to the amp than should be :(
don't really know what to do. I have a bad feeling about this.
If anybody has a possible answer, or knows what I should check now...
thanks a lot.
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Follow Ups:
I admit to being a barnyard engineer, but my first thought is that the buzzing transformer had a winding about to go. If it shorted out it would certainly blow any fuse you put in there. If that were the case hopefully the fuse did its job and protected everything else. Even if it was a little higher rating?
How hard would it be for you to pull the transformer and take readings on the windings? There are people who will rewind a transformer if you can't find a suitable replacement.
Reading the two following links, it seems to me, if i'm right, that an increase of the filter caps from 6000uF to 10000uF would increase the inrush current. Could it be possible that this increase of inrush current is too much for the fuse?
http://sound.westhost.com/power-supplies.htm
Quote from another forum: "There is some possibility that larger caps could increase the line inrush current, blowing the input fuse. Switching to a time delay fuse or slightly increasing the fuse value would fix that."
don't know if i should try it...
Was the amp ever serviced? Sounds like it may need a basic cap job, check of bias readings & DC offset, general check of voltages at critical points.
Edits: 08/13/14
Well I just opened the amp: turns out the PSU filter caps have been changed for bigger value: they're now 10000uF 63V aerovox instead of the original Elna (?) 6000uF 50V. All the rest, as far as I can tell, is original. Smaller values caps haven't been replaced but they look fine (don't have the tools to test them).
Could this be the reason why a fuse blows? should i try with a higher value fuse? what should then be the correct value?
Please enlight me because I don't know shit in electronics...
thanks
Preferably, one that is familiar with your model SAE amp.
In the meantime, I would advice NOT putting in higher amp-rated fuses. You may cause more damage and add to the tech's bill.
Maybe, someone here has this amp. Or has owned one.
Good luck!
I have another MK XXXIB coming, should be there by the end of the week; it is the silver face, non-rack version; That one is however in less good condition and has been modded from 110v to 220v. I doubt that one will work better :-/. Was also cheaper. I hope I won't have to gut one of the amps to use the parts for the other one.
Since your electronic knowledge is minimal and apparently limited to fuse replacement, you should IMMEDIATELY defer to a proper tech.
The 'new' amp should be brought up on a variac unless you can get 100% assurance it was in service recently. Your tech should do this.
If I owned the dead amp, I'd check the bridge rectifier before calling in the tech. But that's just me and not something I'd recommend. You do NOT have to plug it in to do an elementary check on this part.
Too much is never enough
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