Alto TS110A

[JP-Stereo]

This active speaker had an open voice coil woofer and no tweeter output even if the tweeter is fine.

The amplifier board (DM350W+65W) is also the power supply so i verified it first.
All the power rails are fine and both channels are working.
Confirmed solid SD signal line at 4.95 vdc.

Looking at the Preamp board, no "Tweeter Out", this signal should be present at J6 to feed the CN101 "high Input" of the amp.
The "Woofer out" is fine with a strong signal as per the volume.
J6 is the lower white connector on the right side of the pictured board, it's labeled "tweeter out".



This PRE amp board have many differences on the output side from all other schematics i have from Alto.
Without the schematic, it's difficult to follow any trails...
I will begin by removing the J6 connector in order to find and follow a trace...

[x-pro]

What signal are you feeding to the input of the device? The partition frequency is 2.5kHz. To hear or see the signal, you must apply a higher frequency.
There should be a signal on output 1 of U8A if there is an output to the woofer. But U8B, U9, U10 are responsible for HF.
And here it is enough to check the signal at the outputs of these chips, as well as the power supply directly at their pins 4 and 8.

I took a closer look at the photo of your board. There are some inconsistencies with the schematic. But we can try to use an analogy

[x-pro]

https://instrumentalparts.com/repairs/ maybe they have a service manual.

[JP-Stereo]

I will certainly check for the manual, because it's one of Alto most complicated Preamp...

I am feeding one input with Line audio from a CD via a 1/4" TR jack.

I decide to resolder any suspicious soldering then measure/compare the inputs to the outputs of each opamp in order to see where i am loosing the Tweeter line.
To my surprise, all the opamps were functionnal and i got an HF signal at the tweeter output.

I check the Tweeter = no output and measuring 420 m ohm... I will replace it.
Good output with a temporary replacement speaker.

This case look to be solved

Still have to test it for good with a new tweeter.

[The Dude]

FWIW: You can get replacement diaphragms all over eBay for those HF drivers. If I recall, they use a P audio diaphragm.