Pioneer sx 535 receiver

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oldmarantz

oldmarantz

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Joined 2003
monsite.wanadoo.fr/mahifi/index.jhtml
#1
I picked up an old pioneer sx 535 this afternoon And got one pb with it.
when you switch off the receiver there is a scratch for 10 seconds in the left channel.I look at the offset and when I measure the left channel with a multimeter there is at least between 30 to 38 mV and the right channel is stable at 10 mV...pb with a cap? but where?is someone has got the schems of this receiver or a clue to repair it easily...

thanks for your help

Dom.
 
#2
Feedback should take care of the offset unless there is a ground problem or a bad transistor. I doubt that this amp uses an output coupling cap...probable causes are a faulty ground connection at the preamp or amp board, or a flaky transistor in a LTP at the amp input...in which you simply replace the pair.
 
#3
Hi all
I took a look at the amp board this afternoon... don t find something wrong I checked caps Trs but all seems good (it s a little hard without schems :xeye: ) power supply seems good (checked with scope)I ll try to change the PP to see... it s a 2 SA489 2 SC789.
have you got the equivalent tr for 2sa489 (to220 pnp 60v 4a)this tr is Discontinued..

thanks for your help...

Dom.
 
#4
Sounds like you are looking at the output transistors...the feedback is taken from the output and fed back to the input, which is where the correction for DC offset should occur. The input of the amp section is where you will want to look to cure the offset.

Track down a schematic wherever you can. It's worth paying for, and the 535 is a pretty decent sounding receiver once you get it cleaned up, just not very high power.

If you actually found a bad 2SA489, a 2SB858 would work well here. But don't start replacing output transistors to fix DC offset, you will be wasting your time.
 
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