The B board is for the modulator with the integrated channel switch (vertical) The A type motherboards have the RF channel switch on the main board. - Ed > On Mar 2, 2015, at 10:15 AM, Juan Castro <jccyc1965 at gmail.com> wrote: > > Is the B board the vertical or the horizontal one? > > > Juan Castro > Enviado do meu Olivetti Programma 101 >