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Help fixing my pioneer SA-520 amp

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ste2425

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hi

Im new here and found this place searching for help with my amp.
Well i have a late 70's Pioneer SA-520 the other day i was listening to music not loud, i wasn't putting any form of straign on it and i saw a bright blue spark from the left side and everything turned off. Opened her up and i saw a fuse had blown replaced the fuse and again it blew i am at a loss for what to do. I dont have much of an idea with electronics but im handy with a soldering iron if im told what to do. I really dont want to have to buy a new amp i love this thing all and any help would be highly appritiated. Many thanks guys n galls,
ste
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Between the mains transformer and the two large capacitors there are four rectifiers, check and see if any of those are short circuit.

hi thanks for the quick reply. The two at the top in the first picture are very very close i carn't see any form of obvious damge though, should i move then just slightly apart?
 
hi thanks for the quick reply. The two at the top in the first picture are very very close i carn't see any form of obvious damge though, should i move then just slightly apart?

You need to check them electircally with a dvm to see if they are shorted internally...A visual inspection will not reveal this
 
You need to check them electircally with a dvm to see if they are shorted internally...A visual inspection will not reveal this

You need to test them with a multimeter on it's diode test range.

Ok thanks i will do.

edit: I only have access to a DVM for a couple of days when i go back home, im at uni and cannot afford to buy one thats why id rather fix this then buy a new one too, so what else would recommend i test just incase they are fine?
thanks again
 
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Ok thanks i will do.

edit: I only have access to a DVM for a couple of days when i go back home, im at uni and cannot afford to buy one thats why id rather fix this then buy a new one too, so what else would recommend i test just incase they are fine?
thanks again

Notice there's two fuses to the right of the big capacitors, if the power amps had blown, those fuses would blow rather than the mains fuse. The rectifiers are most likely, but failing that it's probably the transformer.

If you don't have a meter (and they are so cheap there's no excuse not to), then unsolder the four rectifiers, and see if it blows the fuse without the rectifiers. If it does, then it's most probably the transformer, if it doesn't, then stick the rectifiers in your pocket and take them to Uni with you, there's going to be big rooms there all full of meters and people who can work them! :D
 
Notice there's two fuses to the right of the big capacitors, if the power amps had blown, those fuses would blow rather than the mains fuse. The rectifiers are most likely, but failing that it's probably the transformer.

If you don't have a meter (and they are so cheap there's no excuse not to), then unsolder the four rectifiers, and see if it blows the fuse without the rectifiers. If it does, then it's most probably the transformer, if it doesn't, then stick the rectifiers in your pocket and take them to Uni with you, there's going to be big rooms there all full of meters and people who can work them! :D

Well thats good news i think, i dont fully understand electrics or even what rectifiers are but if my understandings of what youve said is right then its only 5 compontants that could be at fault rather then the whole thing if that makes sense. You mentioned running it without the rectifiers. Is that recommended? what do they do?
thanks
oh and ill be testing it tonight or tomorrow depending when i get home
 
Well thats good news i think, i dont fully understand electrics or even what rectifiers are but if my understandings of what youve said is right then its only 5 compontants that could be at fault rather then the whole thing if that makes sense. You mentioned running it without the rectifiers. Is that recommended? what do they do?
thanks

They convert AC to DC, it won't work without them - but it's simply to test if the fuse still blows (in the absence of a multimeter).

oh and ill be testing it tonight or tomorrow depending when i get home
 
i have bad and worse news. The bad new is i couldn't test out the chips you asked. The worse news is i dont think its them or the tansformer but the power amp chip as someone mentioned earlier in the thread. My reasons are that upon further inspection i founf out that one of the other two fuse had blown, the one on the left. I remember someone mentioning that if one of these had blown then it was the power amp. Second i took it to a friend of mine who works for an music equipment shop and he said the same. I replaced all fuses and again the mains blew. The other two didnt though. So what now? I truly hope she isn't just scrap now. This amp was amazing blew any modern thing out of the water. I don't care if its going to be pricy im willing to save i just need a fix. Many thanks ste
 
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Try the amp without the other two fuses - if the mains fuse blows then, it's the rectifer or transformer, if it doesn't, then it's the power amp.

Simply replacing all three fuses and watching it go BANG is proving nothing at all, and quite probably causing further damage.
 
it blew ok i believe you now. Right tmoz ill take it into uni and use a dvm on the rectifiers. Are they easy to source if they are at fault?
 
The rectifiers are VERY easy to source - they look like standard 3A jobs (IN5408 or similar).

ok thanks again for the help. Im a bit of a newb i gues you could say and never used a volt meter before. How will i no if its shorted? Would an ok one show a voltage running through it and one thats shorted show nothing?
 
You use the meter on the diode test range, a faulty diode will read almost zero BOTH ways - a good diode will read about 0.7 one way, and over range the other
 
Sometimes the fuses blow because the output transistors are faulty check those transistors before changing the fuses and giving power
 
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