On Mon, 20 Jan 2020 13:04:37 -0800 (PST),
wrote:

Voltage measured at outputs (OUT0-OUT15) varies from 0v to 3.2, 3.5v,
pulses, etc... Mainly same on working and failing board, but like
half of the LED outputs in failing board have like 0.3-0.5v less than
their corresponding in the working board.

I think you just found the problem. The LED's on the working board
are drawing current from the TLC5943 chips and therefore will show a
lower voltage. The LED's on the failed board are not drawing current
and will therefore show a higher voltage. What this tells me is that
NONE of the LED's are connected to a common bus that goes to either
3.3V, 5.0V, or ground. This is why I suggested that you remove the
black plastic insulator from the LED board. Find this common bus that
goes to all the LED's and check if it is connected to one of these bus
lines. Compare the bus DC voltage and waveforms with the working
board to be sure. My guess(tm) is that this common bus goes nowhere.
Maybe a blown trace, blown fuse, blown series protection resistor
acting as a fuse, or failed connection.

I would check the LED but I have no way to tell what model it is
and whether it is driven color by color (R1-R2 / G1-G2 / B1-B2),
or with a common anode and 3 cathodes, or with serial data...
I can't find any marking. So I can't tell what's the supplied
anode voltage

You didn't mention that there were different color LED's. The hard
way to do this is to trace out part of the PCB and produce a
schematic. A better way is to assume that whatever has failed, has
simultaneously affected all the LED's, irrespective of color. My
guess(tm) is still that it's the common bus that connects all the
LED's.

Any other suggestion for further tests will be appreciated

Yes. I should have suggested this earlier. Remove the LED board and
shine a bright flashlight from behind the PCB. Any broken or fused
trace will be instantly visible, unless the broken trace happens to be
under a component. This will also sometimes show bad solder
connections. Try shining the light from both sides of the PC board.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558