Intermittent F70 Error (by 2 users)

Thanks in advance to anyone who can help me with my issue. As you may have guess (given the location of this post) I have a Panasonic SA-HE7 which has served me well for almost three years. However, now after about ten minutes of operation, the power will cut and F70 will display on the screen. The only way to remove this is to power off the unit and allow it to cool, after which I will get the same ten minutes of operation before the problem reoccurs.
Having searched the F70 issue online, it appears that it usually indicates a blown fuse. However, in this case, the user would not be able to use the unit at all which suggest this is not the case. Also, when I remove the case, of the three fuses inside, all appear to be intact.
Another thought I had was that the fan may not be kicking in, hence the apparent overheating, however this is not the case. The fan will start as normal once a certain level of volume is reached.
Any help/ideas/comments that anyone can provide would be greatly appreciated.

Thanks again

James