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how to figure out why my older pioneer receiver keeps blowing the main fuse?

my pioneer receiver SX828 will blow the fuse on the rear of the unit 3A-125volt.

as soon as i turn it on > it turns on for about a second then the fuse blows!!   there is no burnt smells from inside. it is very clean and dust free inside. i know these older receivers run hot, but there is no odors that tell me that something has overheated or blown.  (to the best of my knowledge) !!  i know this is a very technical question and lots of things to check but i thought i would ask !!

thanks, brian....
bksierra62@yahoo.com

jeff-o7 years ago
Be thankful the fuse is blowing - it's preventing your stereo from going up in smoke!

Like the others have already said, it's probably a short or a bad component.  There's no way to tell which one without opening it up and poking around with a multimeter.  If you're not comfortable with that sort of thing (or the subsequent electronic component removal and replacement) then you should bring it in to an electronics repair shop and have them fix it.
framistan7 years ago
I have a pioneer SX 828 too !!!   I bought it in 1974.  That thing is... lets see... about 35 years old.  I have schematics also..   I suspect your capacitors are dried up... or possibly the output transistors are shorted.   Does the fuse blow with NO SPEAKERS connected?  if so, that further indicates an internal problem not external.  I looked at my schematic and the 3 amp fuse powers the INPUT of the internal transformer.  The 1st item after the transformer is the large bridge rectifier... then the large capacitors... then the power supply board.  Some of my schematic is ruined from plastic lamination i put on it 25 years ago... but some is still readable.  If you want schematic you will have to email me and I will copy it and send you as email attachment.  framistan@sbcglobal.net email me if you need schematic. 
NachoMahma7 years ago
.  If it's not the rectifier, check the power transformer (big one near the rectifier) for a short.
I'd start by trying to isolate sections of the circuit. I'd guess at the bridge rectifier on the power supply as a first thing to look for problems with. Sounds like the fuse is doing its job. To blow that fast, its pulling 5 times or so the fuse'r rating.

Steve