With power applied to the system, no sound is heard from either speaker when both microphones are used.

When switch is changed $($position B$)$ to connect the CD player into system both speakers work.

With right bracket at the output of the pre$-$amplifier, no output at the preamplifier is detected by a meter, but there is a signal present at the input to the pre$-$amplifier.

When switch is changed $($position $B)$ to connect the CD player into system no sound comes from either speaker.

When power is applied to the system with the selector switch in position B$,$ a $CD$ in the player, the play mode selected and the volume increased, no sound comes from either speaker.

With the left bracket on the left side of the CD player box, the selector switch is placed into position A$.$ When either microphone is used, both speakers perform normally.

Without additional testing the right bracket can be moved to the input side of each speaker.

A$.$ Right bracket moves to output of preamplifier

B$.$ Move the left bracket to the input of the pre$-$amplifier $-$ the fault is in the preamplifier.

C$.$ Current bracket location

D$.$ Left bracket moves to input side of the power amplifier.

E$.$ The assumption of only single faults means two separate devices cannot fail at the same time.

F$.$ Move the right bracket to the right side of the CD player box. The fault is in the CD player.

G$.$ Put the left bracket on the left side of the CD player box.