CD-4 indicator light always ON?

[elguapo511]

Hi,
As I have mentioned many times, I have a Pioneer QX-949.
Whenever I turn the function knob to CD-4, the red CD-4 indicator light illuminates.
Not when I drop the needle, but as soon as I switch it to cd-4.

Sumpin aint right.

I have opened this puppy up and done sever air dusting, that is the extent of my engineering skills.
How can I attempt to fix this?

 

[Lucanu]

Can you hear any kind of noise when turning on cd-4?
Does it decode properly?

 

[Circular Vibes]

Is there by any chance a television, computer monitor or computer power supply near the amp, decoder, or turntable? I had a similar problem with a JVC 4DD5 and Grado cartridge near my computer/tv setup. Rearranging my setup made a big difference.