Ewaste adventures - LED Monitor Disassembly

Found a 27" LED monitor in an e-waste bin.

How it works:
LED monitors are actually a type of LCD (liquid crystal display) monitor whose backlight is generated from LEDs instead of CCFLs (cold cathode fluorescent lamp).

The LCD contains a large matrix of pixels, each being electrically controlled to pass the white backlight to varying degrees. For example, to produce a black color pixel, no light is allowed to pass. For a white pixel, all light is allowed to pass.

LG Flatron 27EA63V
19V DC, 1.6A external power supply (didn't come with unit)
Manufactured June 2013
Factory ID: LGDGZ (Dongguan?)

DVI, VGA, HDMI, audio ports on the back.
takes external power adaptor. most monitors i've come across have the switching power supply within the unit.

Screen is damaged. Would love to power up this unit but it didn't come with a power adaptor.

Strange, just one screw. How do we take this thing apart?

Pry it apart with a flathead screwdriver.
If you plan to put it back together nicely, tape the head of screwdriver and don't damage the cable bundle that runs to the front buttons!

Back cover removed

As expected we find on the mainboard:
- 1 controller chip [Novatek]
- 1 crystal oscillator for the pixel clock [TROQ 14.3 (MHz?)]
- a few large electrolytic capacitors and the odd inductor
- a large mosfet [D478 chip]
- several small ICs (listed below)
- many small SMT components
Pixel clock explained: https://www.reference.com/technology/pixel-clock-a45118adc9e2c844

Small ICs:
- TI 54339E buck converter (http://www.ti.com/lit/ds/symlink/tps54339e.pdf)
- 8839BMP-C ?
- Winbond ?
the text on these chips are tiny! i'm guessing they are for voltage regulation.

Lift tab to release the mainboard to LCD ribbon cable


LCD matrix controller board (as seen from rear)


LCD matrix controller board (as seen from front)

The backlight LEDs are in a row at the bottom of the screen. This means its an edge-lit display.
Edge-lit vs full aray: http://www.digitaltrends.com/home-theater/led-vs-lcd-tvs/)

Disassembled display. The pieces, from back to front:
1. the LCD screen itself
2. a "plastic sheet that passes light away from the screen much better than towards it" (anyone know of the proper name?)

3. two light diffusing sheets, for diffusing the backlight. (https://www.inventables.com/technologies/light-diffuser-film-rolls)

4. a "rigid transparent piece of plastic" (is this also to help diffuse the backlight?)
5. a white plastic sheet.

2. The "plastic sheet that passes light away from the screen much better than towards it" (anyone know what this is called?) Left: reversed orientation. Right: correct orientation.

4. "rigid transparent piece of plastic" (anyone know what this is called?)

Loading dead 9V batteries

I loaded two dead 9V batteries with a 100ohm resistor for a couple min, then removed the resistor.

Dead 9V Duracell:

Duracell's charge and discharge behaviour is expected. A dead battery discharges similar to a capacitor. Recovery is similar to a charging capacitor.

Dead 9V Energizer:

 
Can someone explain why the "weird" Energizer's charging/discharging? Perhaps it has to do with leaking cells inside the 9V, causing an unstable internal connection within the battery?

Bad Caps

Large electrolytic capacitors are a common point of failure on switching power supplies and motherboards. I have fixed a dozen such examples.

For motherboard, symptoms include:

- Motherboard doesn't power on.

- Motherboard powers on, fans spin, but doesn't POST.

- Motherboard powers on, fans spin, POST succesful, operating system loaded. However one or more caps on the board is clearly bulging.

Before attempting to fix power supplies, make sure to take necessary precautions. One can get a nasty shock touching some components. After unit is powered off, the large cap on the high voltage side will still hold a charge for some time.

For monitor's power supply, symptoms include:

- Plug in power to monitor: "power on" indicator LED turns on briefly, then turns off. No display.

- Plug in power to monitor: "power on" indicator LED turns on, display turns on briefly, then unit turns off.

For desktop power supply, short the green wire to a black wire to turn on the PSU without a motherboard. http://aphnetworks.com/lounge/turn_on_psu_without_motherboard_the_paperclip_trick

Symptoms include:

- low 12V (yellow wires). From experience, 11.9V or below is "low" if the PSU has no load.

- low 5V (red wires). Lower than 5V is "low" if the PSU has no load.

- low 3.3V (orange wires). (rare)

- high -12V, -5V. (very rare)

Musings

Reality
reality is not this
reality is not that
reality is.
therefore
i am not this
i am not that
i am.


Troubleshooting
do not expect.
receive.


Engineering

at school one learns how things work.
at work one learns how things fail.

Fix: Laser Mouse is Jumpy

Symptom: Logitech wireless laser mouse displays a jumpy cursor when moved in any direction.

Problem: laser diodes were covered with dust

Solution:
Wetted one end of q-tip.
Used wet end to thoroughly clean the lasers.
Used dry end to dry the lasers.
-----------------------------------------------

Trivia: I had no idea the fix would be so simple. First I tried turning mouse on and off, resetting it. Then I opened up the mouse to check for dust -> the inside was very clean.

Then I tested the voltage of inbuilt rechargeable battery -> 3.7V
Sticker on the mouse read "Rating: 4.2V", so I put together 3 x 1.4V used AAs -> cursor was still jumpy.

Googled the problem, got the "q-tip cleaning" idea from here:
http://www.techsupportforum.com/forums/f25/mouse-pointer-twitches-jerks-and-sticks-no-matter-the-mouse-453313.htm

Fix: Computer mouse

Received broken ps2 mouse from friend. It's broken cos he seriously twisted up the 6 ps2 pins, don't know how. It's got a very nice scroll wheel, so figured it's worth fixing.

Removed the entire mouse cord and replaced with a working cord scrapped from an old ps2 keyboard. The color code on the internal wires were different, so it took some funny/annoying trial and error to determine which wires controlled the horizontal and vertical movements as well as left/right click.

Soldered the right wires together, used electrical tape to tape off the exposed wiring. Works great, although mouse now has purple ps2 connector, like a keyboard, lol.

PS - for April fool's joke, switch the wires inside a friend's mouse.

Fix: computer speaker sets

Found 2 identical speaker sets in the e-waste. (EP-691H Multi-Media Amplified Speaker System)

Inital test: One speaker set works perfectly fine. The right speaker on the second set doesn't work and the left speaker works (loudly) only when the volume dial is turned to max.

Opened up both sets to reveal what appeared to be the same thing. There were no bulging capacitors on either board. Tested the bad speaker set's right speaker on the good set, and it turned out that the right speaker itself was fine.

Ran my fingers along the bottom of the circuit board, causing the bad left speaker to emit funny cool noises like R2D2. (aka circuit bending) Interestingly, circuit bending the boards of both speaker sets caused similar noises to emit. Therefore I figured that the left speaker was most likely working, so redirected my attention to the board itself.

After circuit bending and playing with the volume dial for over an hour in frustration and fun, I finally decided to pull out my multimeter to test the potentiometer.

Observed:
Pot controls left and right speakers separately (separate circuit leads)

When vol dial(pot) turned from min to max,
Good set's pot: Both leads go from 9.5kohm up to ~13kohm for a bit then linearly back down to about 4 ohms

Bad set's pot: Top lead: 12kohm up to 50kohm then drops SHARPLY to a few ohms, near "max volume"  Bottom lead stays at ~38Mohm.




Results:
- The pots from the two sets behave very differently.
- Resistance and Volume are have an inverse relationship.
- The behaviour of the bad pot's top and bottom leads corresponds exactly to the results of the Initial Test.
Top lead's sharp drop causes left speaker to suddenly have max sound near max volume and stay mute otherwise. Bottom lead stays at a constant high resistance(Mohms), causing no sound on the right speaker, regardless of pot position.

As expected, shorting the top and bottom leads caused max sound on left and right speakers regardless of pot position.



Conclusion
bad potentiometer, need a 9kohm to 4ohm resistor to fix.