Pioneer posted this on it's Canadian Web Site:
Poor wiring connections, bad wires or a bad speaker may cause this.
As you increase the volume, you will increase the amount of current you
are drawing from the receiver. To troubleshoot this issue, try the
following:
-
Disconnect each speaker wire connection. Inspect for any frayed or damaged wiring and replace it.
-
Check the impedance of the speakers; make sure they are properly
rated for your stereo. In most cases, they need to be 8 ohms. Only a
few Pioneer receivers will support lower impedance.
-
If the problem still continues, try these steps:
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Turn the receiver off.
-
Remove one speaker.
-
Turn the receiver on.
-
Increase the volume.
If the receiver overloads, repeat steps 1-4 (selecting a different
speaker each time). If you disconnect a certain speaker and the
receiver no longer overloads, have this speaker checked at a service
center. It could have a bad speaker component, like a tweeter,
sub-woofer, or even a bad crossover.