quad 520 power amp fault help

aardvark

aardvark

aardvark

Soldato
Joined
2 Jan 2005
Posts
8,492
Location
leeds
So, i've had this amp for 20 years and i bought it second hand then, so its old.
Now, it always made the speakers thump a little when turned off, but i moved recently and now when i turn off the right channel is more a crackle fart when i turn off.
Still plays music fine.

i contacted quad and they say send to them, which i don't really want to do because:
a - its 12.5kg and will cost a fortune to send (and likely fix)
b - they have a 12 week turn around anyway

what do people think?
i opened it up and can't see anything dodgy.
i'll probably look for a local place to maybe have a look at it if i can find one, but if any one knows what causes this kind of problem i would appreciate it.
 
well, i think i might have found the culprit.

I took the cover off to take some photos to send to someone and there is a blown fuse on the right channel. Its just above the big capacitors in the picture.
Not sure what it does - i'm surprised it still worked. Maybe it is just to connect to the capacitors so the right channel wasn't using them?

I'll get another fuse and see what happens!

C1PvcgJ
 
Last edited:
Its the normal 520, not the f version, although i'm not sure what the difference is.

I do find it odd that i have a blown fuse and both channels are still working though (and its definitely in stereo).
Its an T2A fuse though, not an FS100.

i know the 520's are notorious for being modified - certainly the xlr pins are connected in a non-standard way.
 
The only thing written by the fuse was a sticker saying T2A. I haven't looked at the back though.
I'll see if i can have another look at some point.
 
Kei said:
It’s essentially the half way point in the secondary winding of the transformer. It gets used as ground as it should sit pretty much at 0V. This fuse going will simply affect the grounding on that channel, which may be why it still works. It’s obviously got another path to ground.
Click to expand...

thanks
 
well, changed the fuse and now everything is fine, no more noises when turning off - except for the usual thump of course.

hopefully it was a one off
 
there is one thing i forgot about, but when i moved i didn't have any sound in the right channel - i traced it to broken solder in the speaker cable connection (because its xlr i soldered my own speaker cables together).

i guess that could have shorted the fuse maybe?
 
just glad thats the likely explanation.
Good to know i don't need to send it to quad - hopefully it lasts another 20 years without a problem.
 
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