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 Post subject: Pioneer SX 850 stereo receiver one channel fuzzing out
PostPosted: Aug Thu 26, 2010 11:46 am 
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How do I solve the above mentioned problem? It was a really nice unit until this started happening.


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 Post subject:
PostPosted: Aug Thu 26, 2010 2:42 pm 
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Clean the tape monitor and selector switches with Deoxit.


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PostPosted: Aug Thu 26, 2010 5:00 pm 
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If the problem is only at low volume levels I would also suspect the speaker relay. This is normally confirmed by turning the volume up when the unit is acting up. If the problem goes away it is because the increase in current demand has caused the relay to close properly. A little cleaner inside the relay or burnishing the contacts would solve the problem.


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PostPosted: Aug Thu 26, 2010 5:50 pm 
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I've got an SX-650 that has just started to do the same thing. Good to know, thanks.


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 Post subject:
PostPosted: Aug Thu 26, 2010 7:25 pm 
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So let me get this straight: The active audio passes through relay contacts? Wow.

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 Post subject:
PostPosted: Aug Fri 27, 2010 5:32 pm 
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It used to happen at low volumes only but now it is a problem all the time. Where is this relay found?


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PostPosted: Aug Fri 27, 2010 5:59 pm 
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When you first turn on the unit there is a momentary delay while the protection circuitry checks to make sure that there isn't a large DC voltage offset in the circuitry before the signal is sent to the speakers. This is the relay that I was referring to. If you listen closely when you first turn the unit on you will be able to hear the relay click when it activates and thus be able to easily locate it. Also, if the relay is indeed the culprit, you can also confirm it by slightly wiggling the relay with your fingers while the unit is acting up. If the problem cuts in and out the relay is bad. The problem could also be, as stated in a previous post, any of the other switches in the signal path or an actual component issue. To add a little bit of history, I had a Pioneer SX1000 that had the same problem. I was convinced that it was a preamp transistor for the longest time until I stumbled across the relay as the actual fault. I later discovered that this was a standard problem with many makes and models.


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PostPosted: Aug Fri 27, 2010 6:03 pm 
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It sounds as though the bias on the driver or output transistors (if that is how it is made) is changing possibly because of a leaky electrolytic capacitor. You may want to see if there is a bias pot and what voltage it should be adjusted to. However, if it is changing, you should find out why; leaky electrolytic, semi-conductor, drifting resistor etc.

I know that I had a Sansui 990 that would sound fuzzy at low volume. When you turned it up a little, it cleared up. I found the bias was off and was able to adjust it. But the pot was nearing the end of its range so there was another cause. I was only adjusting the symptom. I did not have time to fix it, someone else wanted it!

Just a thought...

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PostPosted: Aug Sat 28, 2010 4:18 am 
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I fixed a receiver with similar symptoms by cleaning (Deoxit) the balance control. Wouldn't hurt to shoot all the controls and switches while you're at it.

Chuck


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 Post subject:
PostPosted: Aug Sat 28, 2010 5:36 pm 
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Quote:
So let me get this straight: The active audio passes through relay contacts? Wow.

Yes. All Pioneers of this vintage do that. I have several - SX838, SX-850, SX-980, SX-1010, SX-1280. All have this relay, and it does become a problem after 30 years. :x


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 Post subject: DeOxit worked, thank you.
PostPosted: Sep Fri 03, 2010 12:58 pm 
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i ordered the DeOxit DN5 and tried it . When I sprayed the volume control which was full of crackling (took the knob off and shot from there) then I moved the volume up and down. The crackling got less and less and then disappeared. Then I sprayed all the controls. Now I have my just like new sound back. Thanks for the tip, this stuff is great. I think I'll use it on my 81 VW Rabbit rad fan switch also...


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 Post subject: Re:
PostPosted: Jul Mon 17, 2017 7:39 am 
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Bryantenn wrote:
So let me get this straight: The active audio passes through relay contacts? Wow.


That's extremely common, in fact, nearly ubiquitous, for the reasons stated, particularly, to remove turn-on "thumps" as the power supply comes up. Of course, there are a bunch of audio-nitwits that bypass the relay, then they blow their speaker fuses, or more likely, their woofers bottom out because they remove the fuses, or replaces the 5-amp fast-blows with 20 amp slow-blows, or bypassed them, too, "for better sound". The sound is unaffected by a relay in good condition, weak or defective relays can either drop out, chatter with microphonics, or develop high resistance.

You can design the amplifier to not have a turn-on thump in the first place, but it takes more care in making sure that everything comes up at the same time, and for Pioneer/Yamaha, etc, it's easier to put in a relay.

Brett


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 Post subject: Re: DeOxit worked, thank you.
PostPosted: Jul Mon 17, 2017 7:46 am 
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lwood wrote:
i ordered the DeOxit DN5 and tried it . When I sprayed the volume control which was full of crackling (took the knob off and shot from there) then I moved the volume up and down. The crackling got less and less and then disappeared. Then I sprayed all the controls. Now I have my just like new sound back. Thanks for the tip, this stuff is great. I think I'll use it on my 81 VW Rabbit rad fan switch also...


I have worked on many Japanese audio components from that era and they all have problems similar to this, particularly if they have been sitting unused for a long time. The balance control and the volume controls are the usual offenders, since they tend to use the small Alps (10mm maybe?) controls. I haven't seen any relay failures in this era Japanese equipment, but *many* in "salon" preamps, so I would always consider it a possibility.

I have to hand to the Japanese, no matter what you might think about the audio qualities, this era equipment is surprisingly reliable electronically, and the only real Achilles heel are the controls.

Brett


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 Post subject: Re: Pioneer SX 850 stereo receiver one channel fuzzing out
PostPosted: Jul Mon 17, 2017 12:24 pm 
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Quote:
When I sprayed the volume control which was full of crackling (took the knob off and shot from there) then I moved the volume up and down.
Control cleaner is usually sprayed sparingly into the rear of controls and switches. Spraying from the front does not allow the chemical to reach the resistive elements or contacts. Exercising the controls as you did (even without cleaner) often restores proper operation temporarily. I'm glad that you got your receiver working.

Dave


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 Post subject: Re:
PostPosted: Jul Mon 17, 2017 1:07 pm 
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Chuck wrote:
I fixed a receiver with similar symptoms by cleaning (Deoxit) the balance control. Wouldn't hurt to shoot all the controls and switches while you're at it.

Chuck

I agree, Deoxit all the controls before investing time, money, and effort into doing something unnecessary and possibly damaging. Deoxit fixed the same problem on my SX-636.

Larry

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