Whine when playing video

[m42uko]

It’s cool you have made progress.  I don’t have hardware in hand yet.  I haven’t seen any measurements of the frequency.    I think  could measure a put a high pass filter on sound output. Though your solution to try and smooth the ripple at the putative source is more elegant.

Here are some measurements taken on the supply rail of the PA / USB (on L11):

pa_act: 250 mV ripple @ ~1.5 kHz
pa_off: 250 mV ripple @ ~150 Hz
pa_act_lowest_brightness: 300 mV ripple @ ~1kHz
pa_off_lowest_brightness: 300 mV ripple @ ~160Hz

pa_act_usb_mouse: 300 mV ripple @ ~3kHz
pa_act_usb_stick: 300 mV ripple @ ~4.5kHz
pa_act_usb_raspi: 300 mV ripple @ ~5.5kHz


Here are the corresponding screenshots for some:

Spoiler:

pa_act:


pa_act_low_brightness:


pa_off:


pa_off_lowest_brightness:

Oof, that's actually quite bad. Especially considering the wide frequency range and the amplitude... And even during these measurements, the frequency was anything but stable. I guess we'll really have to take a look at the SMPS...

Does anybody have a datasheet for that one?