The Mac was on for about two hours when the fail occurred. On the right hand side the case was very, very warm to the touch.

Thanks again.

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The right hand side? Is this when viewing the mac normally? The right side shouldn't get hot...

When it "overheats," does the Plus stop functioning altogether, or is it that the display goes dark? For instance, after it fails, does it respond appropriately to the insertion of a floppy (for example)?

And does the Plus always work fine after you give it a chance to cool off?