Further analysis on several V12 has shown that in certain situations the
mechanics controller can fail while communicating with the dvd controller.
You can notice when this happens since the reset button, which is connected
to the mechanics controller, will stop responding and the only way to turn
off the machine is to unplug the power jack.
When the mechanics controller crashes, the dvd controller keeps sending
a pulse train to the tracking and focus drivers which results in a steady
voltage increase on both the tracking and the focus coils.
With the proposed diode fix, this increase is initially limited but if the
user leaves the crashed pstwo on for several seconds the output drivers
will eventually reach saturation and, if the RS2004FS thermal protection
doesn't kick in, the coils can burn from the increased current flowing.