Power for backlight, and speakers

[raspmod]

Thank you for sharing your experiment and the tutorial video! I was able to follow most of the instructions, and I can now use my Mirror as a new screen (via HDMI, without sound)!

However I had a few hiccups and I wonder if you were able to resolve them:

1) Did you find a way to power the backlight directly from the vizio TV mainboard? It seems that the original power supply board and scalar board and used only for backlight at this point; I'd love to be able to get rid of those and control backlight from the TV.

2) By merging the left and right audio cables, aren't you losing the ability to have stereo sound?

Thanks again for sharing your amazing work!

[olm3ca]

I'm glad it worked for you - it's a much more versatile device now, I think!

1. You're right about the backlight - there would ideally be a way to control this from the Vizio mainboard. It would require some work to re-pin the wires from the scalar board connection to the Vizio. With a multimeter perhaps you could test the wires to see what voltage is required and we would then need to know from the Vizio board's spec sheet what it requires. It's fully within reach, just needs some more testing.
2. Correct, it is no longer stereo following my method. This is because the Vizio mainboard apparently has a mono speaker connected to the original TV. The Vizio audio-out was the first thing I tried, but the Mirror speakers require an amp, so the sound was very, very low. Any further ideas on this are welcome!

[raspmod]

1. I think that would be much neater as we could get rid of two boards (the power supply board and the mirror scalar board) and hopefully also be able to control the intensity of backlight from the vizio menus. I have a multimeter but very limited experience with electronics -- I can help get the measurements if I have guidance! What should I measure, and how would we get the two backlight pairs of wires connected to the vizio board? I'm most concerned about possible differences in voltage/current that could fry the LED strips in the mirror.

Here is the board that powers the backlight in the original mirror: it has two outputs (a pair of wires for each) and gets its input current from the mirror's scalar board (which itself is connected to the huge power supply board).

The vizio board has two similar outputs in the "LED driver" area of the PCB, see images below: a three-pin connector (+ - -) and a two-pin connector (+ -; a second - pin is unused)

2. Instead of connecting to the speaker port of the vizio board, have you tried connecting to the audio output (of either the vizio board or your chromebook), while still powering the speakers using power wires from the vizio's speaker port? I'm not quite sure which wires this would be though.

[olm3ca]

1. If you're up to it, I think testing the voltage with the multimeter from the 2x output pairs that go to the backlight strips would be super helpful to know. Also, power up the Vizio and test voltage there too. It's a good starting point at the least. If the voltage is the same, that would tell us something. It may help to run this idea by u/NuQ and/or perhaps others in r/diyelectronics to see if there are any other suggestions prior to implementing anything (if voltage is different).
2. That was my first approach, exactly as you describe. There are four wires leading to each speaker. Red / blue, and orange / black. I figured power would be from the orange / black. In testing, it actually appears that red / blue are for the main speakers, and orange / black are for the tweeter. If I'm correct, these are passive speakers that require an amp. This could be tested more with other options though. I'd be interested in any further ideas.

[jmbherbert]

Regarding the backlight - I'm curious whether one of these would work for that port: https://www.ebay.com/itm/275755918638?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&mkscid=101&itemid=275755918638&targetid=1529314446910&device=c&mktype=pla&googleloc=9032131&poi=&campaignid=19851828444&mkgroupid=145880009014&rlsatarget=aud-1317154473495:pla-1529314446910&abcId=9307249&merchantid=138151680&gclid=Cj0KCQiAw6yuBhDrARIsACf94RXkvZf14aerZRAJthCVutALn6atwMNGn4p_lxz1UYFleREm37k4mEUaAiG-EALw_wcB

[olm3ca]

Good find @jmbherbert - the photo isn't great but I would think it's worth a shot to ask the vendor for any additional details or photos. It would make sense that this board should be able to control the backlight of the panel. With a multimeter reading and this cable, I think it's likely we're on to something here.

[jmbherbert]

Ok - got a chance to put a multimeter on each of the two outputs that run from the backlight strip power, they’re each running at 60V(!) - I guess that’s why the circuit board says “Caution high voltage”…

Also tested the outputs from the Vizio board. They seem to be reading 0.5V, so I don’t think they’re compatible at all. I’m guessing the LED they might be for is the little red light on the front of the TV. So it looks like the scalar board is still going to be required for now at least.

[olm3ca]

Hmm. In thinking about this, I would assume that the small board the panel connects to is what regulates power, so it sends 60V to the panel but the scalar board would only need 0.5V to tell it to turn on and off. It would be interesting to test the wires from this cable, to see what each of them read but specifically the red wire. I'll get to it someday unless anyone wants to test:

[jmbherbert]

I just tried measuring across the two white and red wires on that input set, and the voltage differential was 0V. I suspect you're correct and it pulses on this to turn the thing on and off, but I wasn't able to flip the switch and get the probes on fast enough to catch one.

Irrespective, I'm not sure where we'd get the rest of the input power from without keeping the power board at least. I don't see anything on the Vizio board that's pushing power out? I'd actually be curious to see the inside of a Vizio TV. But for now at least, I think I'm probably keeping the power and scalar boards.

Going to try putting my raspberry pi + relay into the two sets of switch wires next (the black twisted ones that run to the bottom switch and the ones to the Vizio on/off switch). Will report back on how that goes afterwards.

[jeremy-fields]

I have the LM40SAMFHD700AG25WV model which has a different looking backlight board, but the wiring appears similar. It seems like there are multiple hardware variants within the LM40SAMFHD700AG25WV grouping. My backlight board has a large 14 wire input cable coming from the scalar board and 4 wires (2 pairs) going to the backlights. My input cables are labeled on the board so I was able to find ground and measure all of the inputs. There are 5x 24V inputs and 5x associated grounds. All measured 24V whether the backlight was on or off. One of the other input pins (COP) read 3.3V regardless of backlight state. The other 3 pins varied depending on backlight state. Second control type pin (ON) was 2.7V on and 1mV off, next pin (DC) was 1.4V on and 20mV off, and last pin (PWM) was 5v on and 0V off. The output pairs read 52.4V when on and 0V when off. All voltages were DC. There are round contacts right above both cable connections. Found out these are test points. They have similar voltages when I test a round point to a hot point. More photos with voltages labeled: https://imgur.com/a/x5ImJ4j

[mweth]

Roping in Issue 8