Storage [Q] [q] how to disable hsdpa/hsdap+ on s33 mini

I have successfuly tethered my s3 mini on my windows PC, however the change from H/H+ makes the internet connection unstable.
There are suggestions of using the codes *#301279# (HSDPA/HSUPA Control Menu) but this does not work on my S3 mini.
Any help to make this stable would be be very much appreciated. thanks in advance!