Pioneer SX-950 pre-amp damage

MarkTV

New Member
I would love to be able to get this oldie-but-goody receiver resurrected. Its in Mint shape inside and out, very clean, clean glass, no scratches. No known history other than it's been sitting in a Pantry shelf for 20+ years. Need to find my camera and take some pics. It was given to me as a "It comes on, but that's it". I was reading here @ AK about the PC and relay clicks on these and such I broke this 950 out and powered it up to see what condition it's condition was in ;), it came on, then 60 or so seconds in, a big "pop". I personally thought a cap some where poofed.
On the preamp board (AWH-050B), on the right channel side it looks like one of the two 2SA726's has exploded, a lil lower to it's left, it looks like it was a 1/4w 3k (w/riser leads) resistor, has melted. don't know the condition of the C1628-y. Anyone have a clue as why this transpired? Shorted outputs?? I have yet to break out a meter, and probably won't get to this until tuesday or so. Just hoping I could get a heads up :) this SX brings back cool memories, and I have a pair of pioneer speakers from around same era (not original woofers) this thing will kick around hopefully.
Will post some pics here shortly when i dig out camera.
 
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Best shot for an easy fix without a lot of messing around and measurements is to shotgun the board, new transistors, caps and diodes. Pretty inexpensive as long as the output transistors survived. We have no way of knowing which transistors took damage during these events that will pop them soon after the unit is returned to use.

While replacing the transistors (or before) test all resistors for damage WITH ONE LEG LIFTED.
 
Welcome Aboard!

Once your dim bulb tester is built you might want to pull the outputs to test them, and possibly keep them out if they test intact. It will skew some of the voltages in the power amp sections but could save the more costly outputs from damage (if they aren't already toast).

If you had not already caught on, there are fairly complete lists of current replacement components for the unit in several places around the site, such as this:

http://www.audiokarma.org/forums/showpost.php?p=4581960&postcount=4

And this:

http://www.audiokarma.org/forums/attachment.php?attachmentid=393170&d=1354374719

It might also be a good idea to plan on refurbishing the power supply board, so if you have to place an order for components, bear that in mind to keep delivery costs to a minimum.


While replacing the transistors (or before) test all resistors for damage WITH ONE LEG LIFTED.

I've always preferred to do that while comfortably seated, but, to each his own. ;)
 
Didn't you know that's one of the few AUDIO-YOGA positions for checking components, known as "GETTING THE LEAD OUT".

Larry
 
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