I have been doing some failure annalist on my LG HS201 that has died after about 6,000 hours of operation in normal mode. In my previous posts (pictures/short video) the Green LED is not working (connector burnt), the Red LED is flashing and the Blue LED seems to be OK.
Not Knowing exactly where to start I started with the LEDs, I was surprised by some of the things I found. This is going to be a Book, but I want to keep this a paperback so rather than explaining each technology in this post I will give you a link that will explain the technology. I also don’t want to make this too geeky so hopefully between the pictures and my efforts at explaining most will be able to follow, so let’s get started.
Here is the Luminus LED (1 of the 3) used in the projector http://www.flickr.com/photos/4530762...in/photostream
Here is a low magnification picture of the actual LED chip (one of the corners) behind the glass http://www.flickr.com/photos/4530762...in/photostream
In the next series of high magnification pictures I will point out and explain the defects in these LEDs, REMINDER I bought this projector in 12/09, that means these LEDs were made/assembled prior to that time, these problems I point out today may no longer exist in today’s product.
First image is of the Blue LED, take note of the perfect circle in the lower left of the image http://www.flickr.com/photos/4530762...in/photostream
Next image is of the Blue LED also notice the contaminate at the bottom http://www.flickr.com/photos/4530762...in/photostream
In the coming chat about what these problems are I’ll be referring to the 2 images above to try to explain what the problems are, the following images are to show the Green as well as the Red LEDs have the same problems.
The green LED, NOTE a dark spot in the center of each circle (will be part of the explanation) http://www.flickr.com/photos/4530762...in/photostream
Green LED at the edge where some contamination remains (black strings) http://www.flickr.com/photos/4530762...in/photostream
Red LED with same defects http://www.flickr.com/photos/4530762...in/photostream
Red LED with large defect http://www.flickr.com/photos/4530762...in/photostream
Now for the explanation, let me start by saying I’ve worked in the semiconductor industry for the last 32 years, in those years I’ve personally been responsible for resolving these types of manufacturing defects.
Let me start by listing what I DO NOT KNOW, I don not know if this film is an Oxide http://en.wikipedia.org/wiki/Oxide
(SIO2), A Nitride film http://en.wikipedia.org/wiki/Nitride
(Si3N4) or an exotic optical coating for blocking cretin wave lengths of light.
I DO NOT KNOW if this film is for Passivation http://en.wikipedia.org/wiki/Passivation
, if it is used as a “Scratch Coating” (this is a film deposited to protect the device surface during assembly) or and optical coating http://en.wikipedia.org/wiki/Optical_coating
I DO NOT KNOW what method was used to deposit this film, CVD http://en.wikipedia.org/wiki/Chemical_vapor_deposition
, LPCVD (Same link talks about LPCVD too) or PECVD (Again same link talks about PECVD)
This is what I DO KNOW, if this film wasn’t needed it would not be on the chip.
I do know the wafers were contaminated with an organic particle (room dirt, dirty dryer, poor handling, etc) prior to the film deposition, this is not a guess this is a fact and I will try my best to explain this.
The film in the first blue picture has a gray tone to it except in the lower left corner where you see a perfect circle (same circles you see in the other photos), in that circle you see white for a color. The gray is the deposited film and the white is where the film did not deposit (Guess, the white is bare silicon).
The dark spots in the center of all the circles are the dehydrated/burnt/carbonized remnant of that particle after it went through the?? CVD process, this is what happened.
During the deposition of the gray film, very pure gases are used (for Nitride, SIH4 @ 99.999% pure and HN3 @ 99.9% pure), that very pure gas combination comes into contact with the gasses escaping from that organic particle (that can be ANY gas, O2, N2, water vapor, etc) and makes a different compound (Not an Oxide, Nitride or optical coating) that doesn’t stick/gets deposited on the surface where this gas is. The reason why it is a circle is because the emissions of gas is Omnidirectional http://en.wikipedia.org/wiki/Omnidirectional
from the particle meaning the gas extends the same distance around the particle in all dimensions (left/right, up/down).
The particle shrivels up to those tiny (sometimes larger) spots exactly in the center of the circle, BUT does it affect device performance, that was my next experiment. I removed the R/G/B LED from the projector and set up a test bench.
I used this power supply http://www.madelltech.com/TPR3000.pdf
with a TEC http://en.wikipedia.org/wiki/Thermoelectric_cooling
In this picture you can see the basic set up http://www.flickr.com/photos/4530762...in/photostream
the 12 volts on the right is for the fan on the TEC, the fixed 5 volts was for the TEC (tri output supply) cooling it down to 1.6 deg C and the supply on the left was for the LEDs
Red LED at idle http://www.flickr.com/photos/4530762...in/photostream
Green @ idle http://www.flickr.com/photos/4530762...in/photostream
Blue @ idle http://www.flickr.com/photos/4530762...in/photostream
Red @ 4 Amps http://www.flickr.com/photos/4530762...in/photostream
Green @ 4 amps http://www.flickr.com/photos/4530762...in/photostream
Blue @ 4 Amps http://www.flickr.com/photos/4530762...in/photostream
So what do I know @ this stage Absolutely NOTHING, I found and identified the manufacturing defects in the LEDs, but SO WHAT it isn’t the problem.
So I now come back to the burnt connector, I go to Luminus website to copy the PDF only to find out they removed them, I had to call and request a copy (and I did). I wanted this info so I could make this accurate
According to their spec sheet The LED that has to be driven the hardest to reach 200 lumens is the blue LED, it requires about 6 amps where the red is 4.1 amps and the green is less than 2, so now I’m really confused as to why the LED that draws the least current was the one to cook?????? Resulting in this http://www.avsforum.com/avs-vb/attac...7&d=1316283643
One thing I have noticed is the LED side of the same connector had a slight browning around the same pin #s (6-7-8 the MOSFET + switching side).
So I am still in the same spot I was, except I have verified the LEDs still work fine. My next step is to put the projector back together (solder all connectors) and scope out the MOSFETS that drive the LEDs, the PDF is here http://www.datasheets.org.uk/KMB054N...datasheet.html
(2nd PDF in the list).
I plan on sending a uniform RGB bar to the projector and scope out the MOSFETS (I would expect to see the same pulse duration (not magnitude)) if I detect a problem that is before these MOSFETS then it goes into the trash (I would be getting into OEM coded chips and I draw the line of effort there).
Sorry for saying so little in such a large post