Pioneer QX-8000a Hiss in Left Channels

[LegginsWill]

If the volume control controls the hiss, that means the hiss is coming before the volume control, or IN the volume control. Are the tone controls before the volume control? I recall an incident in my younger, more naive days when I was upset that the treble control increased distortion, but was taught that distortion is almost always harmonics (multiples) of the original signal, so the treble control would inherently boost distortion. Not that that’s what you’re experiencing, but an illustration of unintended consequences of some of the knobs we take for granted.

So the volume does control the hiss, it will make it louder or quieter. However, at 4/10 volume and full blast, the hiss is significantly quieter. The tone controls are in preamp right after the volume controls. Which yes, the treble will make the distortion worse.

I attached a picture of the block diagram from the original SM, but it appears the only items before the volume control is the tape monitor switch and the balance controls. I have cleaned the balance controls many times, but the tape switch is a hard one to clean. I have given it quite a few shots of DeOxit but I think it’s time to remove this switch and really clean it.

 

[par4ken]

Dirty pots and switches are common problems with vintage equipment, more so than bad capacitors even. Usually they would cause more of a crackling sound and or intermittent output rather than hiss.

You are limited with the test equipment that you have available, if you had an oscilloscope you could "look" for the noise. With more than one channel you can compare the good side to the bad.

You seem to at least be on the right track. Good luck.

 

[LegginsWill]

After finally ordering new PN2222a transistors, the hiss is practically non-existent. I pulled apart the control board and replaced all remaining transistors and 4 capacitors. I wish I knew exactly what the trouble components were but I just wanted to replace them all in one go. Thank you to everyone who helped and I’m happy to say my first repair was successful!