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 Post subject: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Sun 22, 2021 2:15 am 
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Joined: Aug Sat 21, 2021 8:54 pm
Posts: 6
Faint distortion on left side and looking for someone to repair and or re-cap it. It sounds great with Little David and Yamaha NS-500 speakers.


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Sun 22, 2021 1:50 pm 
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Posts: 11100
Location: Sunbury, Ohio 43074
if you want someone to repair something for you, it might be helpful to know where you are located. ;-)

That said, these seldom need to be "recapped". I'd be more looking for dirty switches and pots, or a transistor issue, or even a problem in the output section of the amp. Need a lot more info to narrow it down.

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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Sun 22, 2021 8:27 pm 
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Joined: Aug Sat 21, 2021 8:54 pm
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I sprayed out the pots and no noise. Also cleaned the RCA's. Speakers are good so i'll spray out the switches next. The distortion is faint when it warms up, you just hear it now and then. I'm in Bakersfield CA. and there three service centers 100 miles away so i don't mind shipping. I've worked for a few guitar tube amp company's building and repairing so i know better then to try and fix it.
Phil


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Sun 22, 2021 8:30 pm 
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Joined: Aug Sat 21, 2021 8:54 pm
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Is ok to a give my phone # and email ?


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Sun 22, 2021 8:43 pm 
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Location: Sunbury, Ohio 43074
Phil Hernandez wrote:
Is ok to a give my phone # and email ?

Personally, I'd avoid that except in a PM when you find someone to help. It is permitted under forum rules, but it's not a good practice since you really don't know who is watching and why, including various bots.

Just let us know what part of the country, or world, you are in so we can possibly help you find some assistance. State? City? That's close enough for the public forum.

Quote:
The distortion is faint when it warms up, you just hear it now and then

Can you describe this distortion a little better? Is it at low volume, high volume, crackling, hissing? What's it sound like, and does it go a way if you turn down the volume all the way. Stuff like that. Also, is it just the phono input? The FM tuner? Set the selector to AUX, is it still there ?

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https://www.bbtvtestequipment.com


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Sun 22, 2021 11:36 pm 
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Joined: Dec Sat 28, 2019 4:18 pm
Posts: 1087
Location: Corinth, TX
Just one channel? Eliminate the sources and you (or someone) may be able to track it down with a scope and an audio signal generator.

John


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Mon 23, 2021 12:00 am 
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cleaned all switches and found that the mode/FM mute switch may not work, i hear no change from stereo to mono and the stereo red light dose not turn on. found no swollen electrolytics in pre or output. Using A CD player through the AUX. Still a slight all most soft distortion in background of left channel.

Phil 661 549-3890


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Mon 23, 2021 2:46 am 
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Also the distortion is hard to hear, faint most of the time and very hard to hear when you turn the volume low. I hear it more in the back round, weak, asymmetrical clipping and a little in the bass guitar. Now i hear it more when it warms up.


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Mon 23, 2021 3:09 am 
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Not enough informations available but it could be crossover distorsion due to improper biasing of the output stage transistors. You should check the output bias current (by measuring the voltage drop across the output transistors emitter resistors, with no signal, volume pot at zero) and compare with the working channel. If there is a bias adjusting (trim)pot it is recommended to clean it and readjust the bias according to the manufacturer's service instructions.


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Mon 23, 2021 3:34 am 
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Joined: Jul Sun 09, 2006 3:11 am
Posts: 7633
Location: Clearwater, KS
This unit uses a pair of STK-0039 large ICs for outputs so advice concerning output transistors and such is not applicable. The service manual doesn't say how to adjust bias or anything else for outputs. Possibly one of the ICs is going bad. Good luck finding a genuine replacement. There are lots of fakes from you-know-where. It will take some trouble shooting to determine the problem.


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Mon 23, 2021 11:08 am 
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Joined: Apr Wed 01, 2020 7:22 pm
Posts: 333
Phil Hernandez wrote:
cleaned all switches and found that the mode/FM mute switch may not work, i hear no change from stereo to mono and the stereo red light dose not turn on. found no swollen electrolytics in pre or output. Using A CD player through the AUX. Still a slight all most soft distortion in background of left channel.

Phil 661 549-3890


Those FM problems are all symptoms of a problem in the discriminator circuit. It could be component value drift or failure, or it could be as simple as requiring re-alignment of the discriminator coils...

It's not an uncommon issue as FM stereo equipment ages...

The distortion using the AUX input is a separate issue...

73...Jordan VE6ZT


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Aug Mon 23, 2021 12:08 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
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Location: Sunbury, Ohio 43074
Recalling that the OP said he wanted to send it somewhere for service, I imagine he may not have the electronics experience to DIY.

That said, the FM problem is usually fixed by a touch up of the alignment, particularly as mentioned the discriminator coils. But you may want to try spraying a bit of contact cleaner into the bearing points of the variable tuning capacitor. Sometimes that's all it takes, as it's not grounding properly due to dirt or oxidation.

The STK modules might be available as a replacement "kit" depending on the actual number. There is at least one company that makes a kit you can build to replace the module. Or you could remove both of them, swap them, and see if the problem follows the module. That would let you know right away if the STK itself is bad or not. Most of them have bias set internally and is not adjustable.

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Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Sep Thu 09, 2021 4:40 am 
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Joined: Aug Sat 21, 2021 8:54 pm
Posts: 6
If you would like to repair it i will be more then happy to ship it to you. i've worked for guitar tube amp company's , Demeter, THD, Divided by 13 and i'm tempted to get one of those cap kits but i don't want the headack.

Phil, Philtone55@hotmail.com


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 Post subject: Re: Pioneer SX-680 receiver low distortion problem,left side
PostPosted: Sep Thu 09, 2021 12:32 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11100
Location: Sunbury, Ohio 43074
Thanks for the vote of confidence, but I no longer work directly for the public.

That said, there are two store front shops here in Columbus, OH, and many more dotted across the country. I'd do a bit of googling and find one closest to you, and talk to them.

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Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


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