That is something Nokta would have to talk to Kellyco about, I have no doubt what so ever they have the expertise to do the work, Dave is an electronic wizard and Barry does excellent work, but I can't speak for Kellyco since I don't work for Kellyco...
I know Kellyco set up an excellent Minelab repair center complete with oscilloscope and custom pressure tank for testing the waterproof detectors.
Just my opinion, but if Nokta really wants a large portion of the US market business which could be huge they need to consider an authorized repair center here in states. Most US buyers are not going to want to a send detectors back to Turkey for repair work and most US buyers do not have the knowledge to open up the controls to change out diodes or oscillators....