[captainclock1988]

I have your receiver's big brother, the SX-1000TD, which was from 1969, and from what I was told was Pioneer's very first solid state receiver ever made, it even has its original box and packaging material with it, the only thing it didn't have was its original manual.

I got mine as a freebie from a friend of mine who owned an ebay store in Warsaw, Indiana and the stereo was given to him to sell by the original owner and he went to plug it in and try it out and it had no audio coming out of the speakers and so he gave me the stereo to monkey around with because he knew I liked to tinker with vintage electronics, but of course the issue with my SX-1000TD turned out to be a little more than I could troubleshoot, so I took it to a local repairman who repaired it for me, and he said the problem was the electrolytics in the capacitive coupling stage of the amplifer of the receiver. 

But the only problem was that the guy who repaired it for me didn't use the correct value capacitors for the capacitive coupling stage of the amplifier on my receiver so when I would listen to it one channel was slightly quieter than the other, but it was barely noticeable unless you were an audiophile nut. 
But later on down the road I ended up taking my receiver into another repair shop who actually replaced those capacitors with the correct value capacitors that needed to be in there and now the stereo plays just like it was intended to.

I also was recently given an SX-737 stereo receiver (and I had also acquired a couple of other stereo receivers as well) and all of those receivers had the same issue you described in your thread where there was a loud crackling noise in the left channel that was present in all of the stages and that wasn't affected by the volume control. 

As it turns out this is a fairly common issue with many different stereo receiver manufacturers, like Pioneer, Technics (Panasonic), Kenwood, Akai, etc. and the issue is in the amplifier board and is actually bad Output Transistors (or ICs depending on whether or not the amplifier uses STK chips for the output stage or actual Transistors) or in some cases its the transistors in the differential amplifier stage (usually some form of an TO-92 Package A992 equivalent transistor that has failed and taken out some resistors in that stage).

I have already bought repaired and resold 3 stereo receivers with this issue and each time it was basically the same parts that failed each time (just different part numbers or differently packaged parts in each unit).

So anyways I just thought I would share my experience with this issue and what I did to fix it.

I hope this is of some help to some people on here that have similar issues with their stereo receivers.