An old skool trick to know if the sync is OK.
Get a piece of cardboard the size of the film gate.
Paint it with some glow in the dark paint.
Once dry, put it in place of the film and point the camera directly in front of the flash.
Close your eyes and fire the shutter.
If the phosphorous material glows, you're in sync. If not, you know somethings wrong.
Flash is synchro at all speeds on a leaf shutter. The only problem might be that it is adjusted for flashbulbs (not X sync). If that's the case, the glow test will tell you for sure.