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 Post subject: Pioneer SX-450 Balance problem
PostPosted: Sep Tue 28, 2021 12:07 am 
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I have a vintage Pioneer SX 450 receiver. Circa 'mid 70s. Suddenly the Balance is weak on the right side. Have multiple sets of speakers on and all connections are fine , Balance is off on all sets. Any ideas?


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 Post subject: Re: Pioneer SX-450 Balance problem
PostPosted: Sep Tue 28, 2021 2:02 pm 
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gdunn123 wrote:
I have a vintage Pioneer SX 450 receiver. Circa 'mid 70s. Suddenly the Balance is weak on the right side. Have multiple sets of speakers on and all connections are fine , Balance is off on all sets. Any ideas?

First, disconnect all but one set of speakers. If balance is still off, disconnect those and try one of the other sets. That way you positively eliminate the speakers as the cause.

When you say "balance is off" ... how far off? The problem could be virtually anything from a dirty balance control, dirty tape/source switches, dirty speaker relays (which I don't think this one has), a blown or weak output channel, or any problem in the entire preamp path. Even a dirty volume pot if it's a dual/tandem pot for both channels.

Is the balance off on ALL INPUTS? Aux, FM, Phono etc? That information would help narrow it down. Input RCA connectors can also get dirty and cause signal loss or death.

My bet is on dirty switches, buttons, or contacts. Before you dive into the electronics, exercise all of them many many times with the power off. If you find this restores it to operation, you might want to follow up with a good contact cleaner for the switches, buttons, and pots.

Then again, if you've been running multiple sets of speakers at medium to high volume levels, you may have caused an output channel to fail. A scope or AC VTVM or even a DMM in a pinch can quickly narrow this down, as you measure the signal level through the audio path inside the unit.

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 Post subject: Re: Pioneer SX-450 Balance problem
PostPosted: Sep Tue 28, 2021 10:35 pm 
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My guess would be one or more bad electrolytic coupling caps in an audio path if Barry's advice doesn't resolve the issue.

Dave


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 Post subject: Re: Pioneer SX-450 Balance problem
PostPosted: Sep Wed 29, 2021 11:49 am 
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Barry H Bennett wrote:
My bet is on dirty switches, buttons, or contacts. Before you dive into the electronics, exercise all of them many many times with the power off. If you find this restores it to operation, you might want to follow up with a good contact cleaner for the switches, buttons, and pots.


+1

I think this should absolutely be step 1 for any 70's era Japanese equipment. I am not entirely sure why, but this era component seems to be disproportionately prone to problems with switches and pots getting dirty or corroding. The balance pot, again, is particularly susceptible, but essentially any ganged pot could cause this problem.

Electrolytic capacitors are step 2, and there are *a lot of them*. These units are all now coming up on 50 years old, that is, *half a century*, and the original parts were nothing to write home about. No one ever imagined when they built them that they would still be around and still in common use even 10 years later, never mind 50.

Brett


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 Post subject: Re: Pioneer SX-450 Balance problem
PostPosted: Oct Sat 02, 2021 7:51 am 
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Are you sure the sound level is too low at the right channel and not rather too high on the left ? (which gives the same unbalance effect).

In such old amps it's very common that weak (opening or low value) electrolytic caps in feedback loops results in increased gain (open loop condition).

If the basic contact cleaning procedure (including all switches, selectors and pots) doesn't fix the problem it's probably time for a complete recap.


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 Post subject: Re: Pioneer SX-450 Balance problem
PostPosted: Oct Sat 02, 2021 12:18 pm 
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Well, since the OP is probably not going to be back, let's discuss the pros and cons of doing a complete recap :mrgreen:
I prefer to find the bad component and replace it. If it happens to be a small electrolytic, perhaps I might consider replacing any that are close to high temperature components, but I've yet to find an amp that needed "a complete recap" to function properly. I suppose the case can be made that these caps will eventually fail, but it depends to a large extent on the quality of the originals, and how the unit was used and stored (heat, humidity, etc).

A novice attempting a complete recap is probably going to have a boat anchor at the end of their efforts. I consider it a last resort :)

but that's just me

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 Post subject: Re: Pioneer SX-450 Balance problem
PostPosted: Oct Sat 02, 2021 5:37 pm 
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I generally agree with avoiding a complete recap, but it is sometimes necessary. I recently worked on a 60's Sherwood S-8800 solid state receiver, and every single small electrolytic was bad. They were either leaky, or had high ESR.

Another example is my Pioneer QX-949 which didn't need a full recap, but there was one particular model of cap which is known to be problematic. Ironically, the bad caps were supposed to be premium quality caps that were only used in critical locations. The general purpose caps were all still good.


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 Post subject: Re: Pioneer SX-450 Balance problem
PostPosted: Oct Sun 03, 2021 7:46 pm 
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Same thing with the bumblebees and Black Beauties -- molded plastic encased capacitors were supposed to be of better quality to be used in critical locations.

-David


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