How can I make my Panasonic SA-HT80 multi-regional ?

I have a Panasonic SA-HT80 that has a Region 4 symbol on the back, however it displays "no disc" when regions 2 and 4 discs are inserted. It does however play Region 1. I assume that somewhere along the line the code has been changed. The problem is how do I make it multi-regional, or at least read Region 4 discs

Sam D
March 2009