Calibrate DTR-1

[alxbob8]

Hello, i'm from holland and i'm using my korg DTR-1 (rack-mounted) for years with pleasure. But i've had a lot of discussions with several guitarplayers about my 440 hz. Ofcourse i allways said to all of them, this korg is absolute 1000% 440 hz. But now i have tested it with a good steady keyboard and with severall other tuners and what is the result?? My 440 hz is NOT 440 hz, but it is about 338 hz, and i have to tune my guitar since a week or to on 442 hz to get it sound equal with other tuners!! How can i calibrate my DTR-1 back to 440? So when i put the power on my 440 hz is exactly 440 hz. Who can HELP me with it??
Stefan