Pioneer SX-950 I have a Pioneer SX-950 with a dead right channel. The problem is in the pre-amp section or at least before the power amp which is good on both channels. No signal appears on the right channel pre-amp out socket on any of the inputs, radio, phono, tape, etc. No signs of loose wires or connections or swollen caps and all pots and switches have been cleaned. Anyone have any ideas.

well you were not clear on the power protection relay at all
and if tripped can never be ignored.

you meant i bet, power protection relay (fires off and activated)
that means these things, (the schematics are clear)
1:speakers shorted,or there wires, test with none !
2: output drivers Audio power amps are shorted, 1 or more.
this is seen as and ******* DC offset voltage to speakers and can wreck the speakers so it trips, saving lost of $$$$ speackers
this is how they all work AVR too .
to find it takes hard work on a beach, with the schematic
and testing each output driver for faults.
the manual shows the tests and good readings, at the driver.
some can trip for over voltage and overcurrent at the power amps.
moved you out of cars and trucks it is no CAR.

Hi George,

I think I'd be looking more closely at the AC / DC section of power supply end of things. Six amps at 120V is about 700 watts and is more than any single channel of the amp. Look at the rectifier for burnt diodes, filter caps for bulging / leaking / etc. Something trying to draw 700W is likely to be a larger component - so I'd look there.

Good luck!

Your problem lies in the power supply of receiver. Check the capacitors and diodes for proper operation.

You need to disconnect the bridges on the PRE/POWER AMP connectors and connect PRE OUT connector to your M4 input connectors.

Buy some electronic contact cleaner in a spray can, attach straw, "unplug receiver" and spray the power button, you may have to remove to be more effective.

HI... NO pre-amp required.
Pioneer made it so you can send the pre-amp signal to a larger power amp ( if you want to)...Either there is a switch to jumper the "pre-out" to the "power in" jacks OR you need to connect a couple of RCA (phono style) cables between them

I reckon the line out is for connecting the pre-amp section to a powered amp. Which is why you are hearing the weak signal. In which case it's clear to me that for some reason the power amp section in your Sonance is dead! Since it's a stereo amp it's something that has killed both channels. Like a power-amp IC such as the picture I'm posting below. Or something else that is accross both channels, but not the pre-amp section.

You need to determine if the power is getting to the audio amp section. For instance with the volume full up is it humming etc?
As a 'rule' it's unlikely that both left and right channels will fail at the same time (unless you have done something silly with the amp) you are looking for something that is common to both channels. Which is why the power section is first suspect. The exception to the rule (above) is where amps use say an IC power amp for both channels. You will find this IC on the big heat sink. Check whatever is on that anyway for damage or burning.
The only other area could be the pre-amp part. Again this could be a single IC controling both channels, so it's failure could cause a loss of sound. By the way if you can hear music/sound coming through when you put it up to full volume the pre-amp will be generaly good.

I have one of these exact amps, more than likely its the volume pot that will need a clean with some WD40 to clean the dust build up inside, try putting the balance on that channel alone and turn the volume up, if the sound kicks in or trys to kick in, this will be the problem or the track inside the pot maybe very worn on the lower setting, which will need then replacing, remember these amps are around 40 years old and chances are it has done a lot of work, if this doesn't fix the problem, as the previous post said it may be in the power amp section and could just be a dry joint on any of the componets, you can pick up all the componet parts fairly easily and cheaply nowdays anyway, let me know how you go.

You need to determine if the power is getting to the audio amp section. For instance with the volume full up is it humming etc?
As a 'rule' it's unlikely that both left and right channels will fail at the same time (unless you have done something silly with the amp) you are looking for something that is common to both channels. Which is why the power section is first suspect. The exception to the rule (above) is where amps use say an IC power amp for both channels. You will find this IC on the big heat sink. Check whatever is on that anyway for damage or burning.
The only other area could be the pre-amp part. Again this could be a single IC controling both channels, so it's failure could cause a loss of sound. By the way if you can hear music/sound coming through when you put it up to full volume the pre-amp will be generaly good.