I have 2 Pioneer SX-3900's with the same problem. With the balance control dead center, one channel sounds louder than the other (the meters support this fact). On one receiver it's the right channel, on the other it's the left. On one receiver I have already changed the 2-main filter caps & adjusted all voltages to the proper settings. While the serviced receiver played fairly well when cold, after it warmed up, the receiver reverted back to it's unbalanced condition. I have not touched/performed any other service to this/these receivers. Any ideas on how to solve the unbalanced channel problem?

Do you have dirty switches/pots?

No. All pots & switches on both receivers are clean & noise free. Both receivers are immaculate inside & out.

Have you checked bias and offsets?

I have a SX-3800 which is very similar in design only less powerful. It had the same problem you describe. The pots were fine, it was the pushbutton selector buttons these use instead of a rotary selector. Pretty hard to clean those up though (kinda sealed up), I think I used a half can of deoxit on it. You may also check the extension shaft that runs from the selector button to selector switch, they have several notches in them where they slip over the switch, if they are putting any tension on the selector switch it may cause you problems also.

Just had another thought, my sa-8800 integrated amp kinda had this problem only once in a while. In this case it was the pre-amp/power-amp jumpers on the back panel. Pull them out (power off) and give it a shot of deoxit. They may have been in there for the last 25 years and may be oxidized.

Another thing to try may be checking the pre-out signal for even output, this may help you decide where the problem is occuring. Same thing goes for the "adapter" loop only the 3900 has.

checked bias and offsets? I reset everything by the book. Jumpers & jacks are fine. The pre-out signal sounds about right. Where do I go to make adjustments? I'm a guitar amp guy. Audio receivers are new to me, although, I'm learning fast! LOL!

As we speak, I connected an SX-850 preamp to the SX-3900 output. The preamp of the 850 is now in front of the 3900 power amp w/speaker connected to the 3900 (p-amp). Stevie Ray is dead-on for both channels! So, my assumption is that the problem is in the preamp of the 3900. Great! Now what? LOL! I'll pull the panels & flush the balance pot on the 3900 (it's attenuating the stronger channel when trying to adjust the balance), but, I don't think that's the problem. I guess I could find & check the supply voltage to both channels. Any other ideas?

technut is right. the switches on a 3900 are a pain to clean and will cause your problem. i cleaned mine on time alont time ago. used wd40 when i did not know any better. but it worked. the switches and push buttons on a 3900 are hooked to cables. the switches are in the back of the unit. the switches just move the cables that control the real switches in the back. it is a pain. :( and most likely your problem. as i had the same thing happen 10 years ago.

chris

I saw the Rube Goldberg push button switch routine. I'll give cleaning the controls a try. Should be interesting. To me they look sealed! I'll have to give this closer inspection.

As we speak, I connected an SX-850 preamp to the SX-3900 output. The preamp of the 850 is now in front of the 3900 power amp w/speaker connected to the 3900 (p-amp). Stevie Ray is dead-on for both channels! So, my assumption is that the problem is in the preamp of the 3900. Great! Now what?

Just had a 3700 6 months ago with the same sort of trouble.
It ended up needing three different things. First clean "all" switches and
pots with deox it. The switches are not completely sealed so the cleaner will
get inside of them. There's usually a small hole some place or you can go
through the front of the switch itself where the plastic rod slides in and out.
This will not be an easy job but will be necessary.
The next thing I had to do was replace the electrolytic caps in the preamp.
Actually I ended up having to recap the entire receiver in order to correct this
problem and some others it was having. Finally I had to reflow the solder connection on the board. Once completed it’s been running like a champ
ever since. Your receiver may not need everything I listed but I would
make sure at least all the control get a good cleaning.

Thanks Glen. I'll do as you suggest. I've already changed the main filter supply caps. I'll replace the little guys, too! These are two beautiful receivers. One is going to a friend, the other I'll keep for myself.

Thanks Glen. I'll do as you suggest. I've already changed the main filter supply caps. I'll replace the little guys, too!

If you're going to recap anything in these units keep a close eye on
the capacitor polarity. I found a couple of spots where they have the
+ sign printed on wrong side of the board. So dont pull all of the caps out first. Replace them one by one so that you dont make a mistake and
get one in backwards.

Later

I just now re-opened the SX-3900 to clean the extended push controls on the back board. Instead of trying to shoot chemical from the front (impossible at best) to get into the control, just gently pry away the sides of the white clips holding down the cover of the control. Flush it out with what ever, blow out with an air conpressor, install cover, snap the clip(s) back into place & you are good to go. No waste, mess, or heavy cleanup. Quite frankly, I don't understand how these controls would effect the balance, but, I'll try anything before surgery.

Quite frankly, I don't understand how these controls would effect the balance, but, I'll try anything before surgery.


Ive had dirty high and low filter switches completely kill a channel.
So yes try this first before you start slinging solder

Signal flows through these switches, whether the function is engaged or not.

I'm making reference to the mode switches: am-fm-aux etc. Well, I bit the bullet & dismantled the front panel from most of the controls & chassis; a real P.I.T.A. with these 3900's. I was able to to flush all the controls. Quite frankly, I was after the balance control. The left channel was attenuating (passing less signal) considerably more than the right. Not only evident to my ears, but also on the meters. The balance control just made it worse because it had to drag the right signal down way too far to balance the output. After flushing everything & blowing out the excess, re-installing the controls, setting the dc balance & idle/bias current again, the damn thing plays like it should. I want to thank everybody here for their contributions. You have all forced me to think in "stereo" instead of mono as in guitar amps & dual mono power amps! LOL!

Incidently, the little "tranny" underneath the main power/filter caps in not really a tranny (as a few people made reference to here in this forum). It is an inductor or 'choke' as called in the guitar amp world. It is part of the dc power supply. It resists/opposes any current changes, & works great for smoothing ripple current (along with the large filter caps, which I 'ALWAYS CHANGE') after vac is rectified into vdc. A nice added feature for this receiver.

If you're going to recap anything in these units keep a close eye on
the capacitor polarity. I found a couple of spots where they have the
+ sign printed on wrong side of the board. So dont pull all of the caps out first. Replace them one by one so that you dont make a mistake and
get one in backwards.

Later

You'll soon find out if you do as the cap in the wrong way will go sizzle and bang :yes: