Prova questo config.txt a me funziona
dtparam=audio=on
hdmi_drive=2
hdmi_force_edid_audio=1
hdmi_force_hotplug=1
disable_audio_dither=on
gpu_mem_256=128
gpu_mem_512=256
gpu_mem_1024=256
overscan_scale=1
dtparam=i2c_vc=on
dtoverlay=pwm-2chan,pin=18,func=2,pin2=19,func2=2
dtoverlay=vga666-6
dpi ...