Logitech Z333 2.1 Speakers

[thyaguster]

Hi there, need some help fixing these Logitech Z333 2.1 Speakers.

They stopped outputting any sound suddenly, tested with 3.5mm jack and with RCA cable.
If I connect headphones to the 3.5mm socket in the volume control PCB while playing an audio book - I can hear it very faintly, can't make out any words, but I can hear the narrator speaking. It does this whether I have the speakers on or off.
The PSU always had a buzzing sound, to the point I could clearly notice a difference in pitch when I turned my speakers on or off.
Since they stopped working I can still perceive a difference, but I have memory of it being much more noticeable. The amp board gets 17v from the PSU, the value doesn't change with on or off.
I've tested with a 19v laptop adapter and got the same results.
Tried to jump wire VOL_RIN to VOL_ROUT and VOL_LIN to VOL_LOUT to exclude the volume control PCB and it's cable but also got the same results.

[ambrosia heart]

I've tested with a 19v laptop adapter and got the same results.
Never do this, extra 2V is high enough to make chips damage. Give marked working voltage to chips.
You make faulty area larger, otherwise. Now you need to check ALL chips if they are working or getting hot.
If chips get damaged, Vcc shorts to ground always as well as hot.

How to troubleshoot, see photos
Download 1KHz wave file and input to the speaker via smart phone.
Then follow copper foils to see where signals go
that are inputs where it may be pre-amp or filtering caps.

Oscilloscope will be a great help when troubleshooting audio equipment. 
If you have it, use it without any hesitation.
If chips are OK, check their peripheral SMD components.


I will leave police station and meet Ada Wong again tonight .