Strange behaviour of v1.7

[BLL]

Hi
I have just moved from fpc 3.1.1 and lazarus 1.5 on a RasPi model2 B to fpc 3.0.0 and lazarus 1.7 on a RasPi model 3 and I am seeing some very strange goings on:
I have an application I wrote on v1.5, which works fine on the model 2.
I copied a folder containing all the file across to my model 3. It opened and built fine in v1.7, but on running it, I find that no data is coming from the 2 USB ports it uses (they are fine under putty), the close button to exit the program stops it executing but then hangs and I have to stop the process! I set up a timer thread in one unit, which was fine on model 2 but doesn't run on the model 3.
I then tried creating a new project and adding all my source files, in a new directory. It builds but gives a sigseg error as soon as you try to run it.

Any ideas please?

RasPi model 3, Jessie, fpc 3.0.0, lazarus 1.7