Help me out here gang, I'm trying to figure out what is causing a low left channel on my SX-3900. Here are the symptoms:

I noticed a few times recently that the left channel was putting out less output than the right -- not a lot, maybe 1 or 2 clicks worth on the Balance pot. When it happened prior to today I could play with the balance knob and that would bring it back.

Today playing with the balance control didn't help. Just by chance I started playing with other controls and found that the "Tone" switch that bypasses the bass and treble was at first intermittent in function, before going away completely in the off position. But when it did (i.e. Tone defeated), the balance problem also went away.

To further confuse the issue, I switched functions from Aux (I was using a CD player) to FM and the Tone control suddenly started working again, with no balance issues. Dear me...

I shut the whole thing off to ponder for a while. Then when I turned it back on, everything was fine, Tone worked on all functions, no balance issues. I'm stumped.

It sounds like a dirty switch, somewhere. The pushbutton function switches, I know, need to be accessed from the rear to clean them. But what about the tone switch? It is a typical Pioneer bayonet switch. Do you clean these from the front?

Type 'de-oxit' into the forum search function.

Type 'de-oxit' into the forum search function.

No disrespect intended, but don't you think I already DID that? Let me clarify, because I am asking two specific questions:

1. Given the symptoms noted, what switches/controls specifically are the likely culprits?

2. How do you access a bayonet switch for cleaning?

I wouldn't expect to find an answer to the first one, and I found nothing specific on the second.

No disrespect intended, but don't you think I already DID that? Let me clarify, because I am asking two specific questions:

1. Given the symptoms noted, what switches/controls specifically are the likely culprits?

2. How do you access a bayonet switch for cleaning?

I wouldn't expect to find an answer to the first one, and I found nothing specific on the second.

Apply de-oxit to all of them. It doesn't make any sense to just do one or two.
To access many of the switches, you will have to remove the bottom cover and the faceplate. Also, you may have to pull down the tone board to access the tone switches and pots.
Don't limit your searches to the Pioneer forum. Try Vintage Solid Stage, General Audio Discussion, and some of the other manufacturer specific forums.
There are dozens of threads on the subject.

Take the time to open the bonnet and LOOK at the 3900. It is an involved job to deoxit all the switches, and YES all the switches need deoxiting, almost ALL of them carry the signal at some point, and if one has gotten bad enough to goof up the signal, the rest aren't far behind.

Getting at most of them on this model is a pita, complicated by construction details. It is shoehorned together at the front and the rear, with a somewhat open center that doesn't help access.

Pray that the volume and balance controls are ok, the balance control is quite unique and is no longer available. The volume control isn't much better.

Once you have looked inside, we can discuss things more intelligently.

Once this thread has run it's course THEN maybe here will be a step by step guide to deoxiting the sx-3900.

Be SURE to get faderlube (MCL5S-H6) "F5" at the same time you get the deoxit.

I have the sx 3800 ,and this was my first reciever I decided to try and clean ,it had issues with one weak channel also ,I found this one to be a little harder to work on so be patient ,Knobs were very hard to get off to start with and after cleaning still had issues , dug into it a little further based on some old threads and found there are 2 larger ,I cant remember exactly but they are grey connecters going into circuit board larger style connector ,I found them to be loose and needed a good cleaning and used electrical tape to help them stay put since the retainer clips were kinda loose,hopes this helps.....