Problem with NEC 2500A

I have a problem with my DVD-writer It noemally burns 8x + and 8x - .
It used to word fine but last week I updated my firmware to 1.07 But know he writes at 1.6 x max. The buffer runs emty everytime I write and then fills up to 50 -70 % and this during the whole process

does anybody has an idea to solve this ?

Sounds like something went wrong during the update or it was the wrong firmware.
Look at the NEC sub-forum. There is a large amount of information regarding firmware for this drive. I recommend using one of the newer 2510A firmwares. Your 2500 can accept them no problem. I personally use mad dog 2F7 with good success.

Make sure and power down your computer after the firmware update. Often a hard reset is required for the firmware to work properly.