Pioneer SA 8500 (KCU} model

[b1jqxk44]

I'm getting a crackling sound on the left channel only. The crackling sound gets louder and the amp shuts off.
I have tried bypassing the pre-amp and I have the same crackling on the left channel of the
power amp, so I know it's in the left channel of the power amp.
I'm going to try to clean the power amp board, (looks pretty gunky) to see if that solves the problem.
I need to know if there's any other test I can try? I do have a digital volt meter.

I bought this amp new back in 1976. This is the first problem I ever had with this amp.

 

[Mooly]

Check for poorly soldered joints on the PCB particularly around components that run hot. Tapping and applying pressure the board with an insulated plastic tool is worth doing however be aware that this type of symptom can be the precursor to more serious issues. If the amp suddenly produces DC at the output then the speaker may be damaged and the amplifier also may suffer damage.

Other problems could include a failing semiconductor (transistor), typically the one in the VAS stage (which runs hot) or the small transistors used around the input stage. Does the 8500 use FET's at the input ?

 

[b1jqxk44]

I'm going to check for loose solder joints with a plastic tool and get back to you. I've cleaned off the board
already and it was dirty. No FET's at the input.

 

[b1jqxk44]

Problem solved, a loose capacitor in front of the VR1 adjuster. Thanks Mooly.

 

[Mooly]

well done. That sounds a little different the usual type of problem.