My SX-950 Pioneer blows main power fuse. Pulled all the fuses in power supply and no change. Could someone guide me in the correct direction, please? I have experience with stereo repair but was a lo

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I have a pioneer sx-2300 in my case the symptoms were powers on you could hear relay click but no output and display was spazzing out flicking on and off or partial image on display I found a fried diode in 5 v section of power supply labeled (D607) on pcb. Replaced and that seemed to do the trick. Hope this helps someone. People always say “ fuse “ or “loose connection “ sometimes this is the case but in my experience it’s usally a little more advanced issue than that.

If you've disconnected everything and the amp is still blowing fuses you'll need to have a technician look at it. Most commonly I find that condition caused by a failure in the power supply section of the amp.

Good luck.

Hi George,

I think I'd be looking more closely at the AC / DC section of power supply end of things. Six amps at 120V is about 700 watts and is more than any single channel of the amp. Look at the rectifier for burnt diodes, filter caps for bulging / leaking / etc. Something trying to draw 700W is likely to be a larger component - so I'd look there.

Good luck!

Fuses blow due to an overload. Generally caused by a short circuited semi-conductor. The most likely cause in your case is something in the power amp section. Chances are something on the heat sink. The device might even have blown up! But if the amp uses transistors in that stage you can easily check these with the multi-meter. All you have to do is put the test probes on the terminals and on the Ohm setting you get a reading like you have touch the probes together - then you have found the shorted part. There might be more than one that has failed so test all the transistors. Anything connected with the power supply can cause the short. But since the biggest cause of fuse blowing in power amps is the main output stage I wouldn't bother with the power supply till you have eliminated the power amp. Failure of devices in that section is also linked to faulty speaker wiring so check that too.

There must be a diode that is faulty in the power supply section mainly on of the rectifying diodes.
If you look closely at your board you will see four diodes that just after the fuse and befroe the Big capaictor(filter cap.) One of these four diodes must be faulty as the fuse keeps blowing. the diodes are responsible of current limitation drawback. So there must be current flowing back to the fuse that makes it keep blowing.
Check and replace. Good luck
Thanks for using Fixya.

G.

check the relays

Check the area where the fuse was...it's usually marked on the board or next to the fuse holder. Check the size also, 2 types 5x20mm or 1/4x1 1/4 in. Usually slow blow.

Yes, check the incoming fuses over by the main power transformer first.
If the fuses are good, the next check will be power switch and then transformer itself.

Speaker Relay Output Switch was a common problem with most SX models of the 70's. It's the switch you hear click on after about 4 seconds of power switch being turned on. It's still avail. thru Pioneer parts for around $45.