C70 Pro-logic Centre Speaker

Hi,

I'm new to this group and was wondering if someone could give me some advice
on the pro-logic system in my '89 C70.

The problem is that when i'm playing music at any volume, the sound is great
out of the normal speakers but goes extremly quiet at certain points of the
cd, as though the centre speaker isn't being amplified or is 'blown'. I have
pulled the control knob fully out and turned it to max and it makes no
difference. It appears to be the same on pro-logic and 3ch. If I play a cd
without either, there can be gaps in the music, where i assume it is mean't
to be playing through the centre speaker.

As you can imagine, this is very irritating, and ruins what would be an
amazing sound system.

Does anyone know if there is an easy way of testing the speaker and if it is
easy to replace, as i don't want to force the plastic covering and
break/scratch anything!!!! If all else fails, how can i disable the centre
speaker?

TIA

Philcol