 Hacking TV backlights
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Conundrum
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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
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Hi all.
I found a broken S*s*ng out of warranty TV with bad backlight.
2 months ago, patched it enough to last until now but it has sadly failed again.
My current plan is rather than playing whack-a-mole with failing white LEDs, replace the entire backlight
assembly with custom RGBW Neopixels or probably APA102C RGB /RGBW as they are more efficient and use
homemade Neopixel+ LEDs with UV nail varnish covers to get the diffusion right (tested!)
As this is a very extensive modification need to ensure safety, my modifications will be fused on each strip and
additionally have overheating protection that reduces LED brightness in the event any more failures occur.
Plan so far is to put them in blocks of 4S4P with a regenerative buffer between each pixel APA102C or APA103 to
allow contrast and brightness setup for each colour and preserve the existing backlight supply and diodes.
As the back of the TV is easy to access I can probably implement amb**ight via optical fibre as well or just use
any leftover diodes here.
Other advantage would be that the TV can be used in HDR mode and/or general accent lighting without having
a separate unit just for this purpose due to the near transparency of the panel when driven to full white "TEST"
mode or simply unpowered works quite well.
EDIT: Also added some glow-in-the-dark strip for diagnostics purposes as ZnS:Cu and to a greater degree
Sr2AlEuO5 is well known to be temperature sensitive.
Hopefully this will prevent any more backlight failures and allow me to monitor diodes for any signs of failure.
Should I add the missing capacitors across each strip as it appears these were left out for cost cutting reasons.
I could feasibly add in a tuned circuit that emits RF at a designated frequency so diode current can be monitored
using an SDR on a low frequency eg 13.555-13.565 kHz in 1 kHz steps.
My SDR is known not to work in this band but the second harmonic should be fine for this at 27.12 MHz centre.
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