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The U-99 message on a Panasonic (as well as F-61, F-63 and F-70) are all indicative of a power supply board failure in the DVD recorder per Panasonic's service manual. That said there are no pushbutton fixes for this and it does require repairs made to the unit to remove the error and allow it to operate normally again. The most common cause of this issue is failure of the two filter capacitors, and in some cases the regulator IC chip in the power supply circuit. The average cost for this type of repair is in the $150-$175 range and generally not considered cost effective to repair unfortunately. The only other thing you can try on a user level (if you have not tried this already), is to leave the recorder unplugged from power for an hour or longer in the hopes this drains residual current from the unit and resets it. Beyond this, it does require repairs as indicated above- and replacement is typically a more cost-effective route to take.
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