On Jan 30, 8:41 am, Tim Schwartz wrote:
Stevie D wrote:
There seems to be a problem with the tone controls, specifically 'high
cut', 'low cut' &
'-20 db' switches also the 'tone on/off' switch. Whenever one of these
is activated, even
at 0 volume, a loud pop is heard and of the spkr relay kicks off
momentarily. There must be
a coupling cap somewhere that's not surpressing the transition noise
that directly affects
the mains output. Can someone shed some light on this. All other
controls operate normally,
no crackling of the volume pot or scratchy bass & treble controls. I'm
stumped!
Cheers, Steve

Steve,

In older Pioneer receivers I've seen lots of leaky low value Sanyo
electrolytic caps, usually 2.2 uf or lower, and 25 volt. I'd change
them in the tone circuits, and at the input to the power amp, if they
are present. These caps are usually a light blue-gray in color, and
have a odd looking seal at the bottom, not the typical rubber, but sort
of like a shiny black goo that dries hard.

Remember, it could be DC coming in before the switches, or DC getting
out after them.

Regards,
Tim Schwartz
Bristol Electronics

Thank you for the hint Tim, I've always checked for bad esr on
electrolytic caps in older amps, I'll check the ones you've pointed
out.
Cheers, Steve