Arjan wrote:
Hello,

I am trying to repair a Philips LX3000D surround system.
The first 15-20 min. after switching on, the system doesn't produce
sound.
All functions work, the volume is adjustable (according to the
display).
Switching mute on or off doesn't make any difference.

During this period I can hear some background noise from the speakers,
so the amplifier works. Via the speakers and also via a headset.

After 15-20 minutes I hear a "plop" sound, after that the sound is
back!
Then the sound will stay.

I sprayed with cold spray on various components but the sound did not
go away anymore....

After switching off (for 10 minutes or so) and switching on, the sound
is gone again....

What is the problem?

Could possibly be a bad solder joint that doesn't make contact
until something warms up and expands. Check the contacts for
the components that have or are mounted to heat sinks.

Sometimes bad joints are nearly impossible to see. You could
just go over them with some flux and a soldering iron to be sure.