Eliminating the inverter board

[hansen01]

I want to build a direct lit led backlight matrix for a westing house lcd that the inverter board or lamps have gone out on. Is it possible to remove the inverter board or are there other functions of the inverter board that it will have to remain connected for? Also where can I draw from to power the leds without fitting another power supply into the tv case? Can I tap into the inverter board (if left in) or perhaps the power supply to the inverter board (if removed)?

[cashkennedy]

Re: Eliminating the inverter board

The inverter board on almost all tv's reports back to the main board that all the bulbs are functioning. If the board doesnt not report its working for ~ 1.5-3 seconds the tv shuts off.

You would have to figure out how it reports that, and come up with a way to mimic that signal. Could be as easy as connecting 2 wires with a resistor, or could be fairly complex.

[hansen01]

Re: Eliminating the inverter board

Is there a place to get the pcb diagram or schematic?

I have searched but the inverter board is so notoriously junky that all I can find is replacements for sale. Seems like at this point it would be more fun and worthwhile to wire up some leds in parallel (possibly cheaper as well).

[budm]

Re: Eliminating the inverter board

You may try contacting this person to see how he does it: https://www.badcaps.net/forum/showth...led+backlights
Did you try disconnecting the power cables to the inverter board to see if the TV will come on and has sound.

[bigdozer]

Re: Eliminating the inverter board

If the tv still has a picture with a flashlight and has sound you should be good. My power supply had the inverter built into it. The ccfls went bad. I'll try to load some pics in my thread in a minute.

[bigdozer]

Re: Eliminating the inverter board

Whats the model number of your tv?

[budm]

Re: Eliminating the inverter board

@bigdozer, you did not happen to take any pictures of how you did it? Do you also have the info on the LED you bought from Amazon? Thanks!

[bigdozer]

Re: Eliminating the inverter board

I took a couple of the busted ccfls and some of the tv working. I completely forgot to get some when i had all the diffusers and bare panel out. I have extra boards for this tv that i could take pictures of but the power supply would really be the only relevant one. I tore the screen all the way down to get to the small metal channels that hold the ccfls. One on top and one on bottom. Each one held two bulbs so there were 4 bulbs total. Took those out and cut the led strip to fit. Wired top and bottom led strips together and soldered the ac adapter connector to the end of the wires. I drilled a hole big enough to get the connector through the back casing of the tv and powered it with a 12v dc power supply. Search amazon for "flexible light strip 300 smd bright white led ribbon 5 meter or 16 feet by ledwholesalers 2026wh". They were something like $16.
I wanted to find the 12v from the boards inside the tv but i'll try that later.

[hansen01]

Re: Eliminating the inverter board

Good info.

@bigdozer: its a W32701 westinghouse


@budm: has sound and picture. no backlight however.

Will edge lighting be bright enough on a 27"? I was planning on soldering up a matrix for direct lighting. Really would like to find a schematic.

[budm]

Re: Eliminating the inverter board

It sounds like bigdozer TV has small screen since it only uses 4 lamps like typical LCD monitor. Your is 27" so more likely the lamp assembly will be right behind the panel.
Ah, it was a 19" TV which uses edge lit, 22" and smaller use edge lit, 24" and up use direct back-lit.

[bigdozer]

Re: Eliminating the inverter board

Yeah my tv is a 19". I would give it a try by edge lighting the westinghouse. You have to make sure you have room to put the leds in the frame for the panel without crushing them when you reassemble the tv. I would think if you back light it you would clearly see the leds. Maybe the bulbs aren't directly shining onto the back of the panel? You wont know until you tear it down. When i get home i have a 37" panel from a magnavox that im gonna take apart to see where the bulbs are and if they shine directly onto the panel. Keep us updated.

[budm]

Re: Eliminating the inverter board

He can do edge lighting if the panel uses the acrylic reflector plate which is used in the LCD monitor, but it will not have that plate in the LCD TV PANEL. The newer edge lit LED TV does use the plate. His panel works like a light box setup.

[bigdozer]

Re: Eliminating the inverter board

Reflector plate. Thats what i was thinking of.

[tibimakai]

Re: Eliminating the inverter board

I have never looked into it, but if I remember there are some videos on Youtube about replacing ccfl to LED on a monitor and there is a place(most likely found it on Ebay) where they sell these kits, but they are not cheap.
http://www.youtube.com/watch?v=ETL8q5nq1ro
http://www.youtube.com/watch?v=h4x6G...eature=related

[cashkennedy]

Re: Eliminating the inverter board

To do edge lighting you have to have a special acrylic plate that take light in 1 direction and slowly reflects it in the opposite direction. This comes with edge lit screens, but back lit ones just come with a basic peice of acrylic and some filters...

(this is essentially what budm just said)

[hansen01]

Re: Eliminating the inverter board

Exactly. You can't edge light this model. I tore it down last night. The ccfls are about 2.5 cm apart and run the length (horizontally) of the screen. They set back about 1.5-2 cm from the diffusers. I figure as long as I keep the spacing of the leds to less than 2.5 cm the diffuser will sufficiently disperse the light and there will not be bright spots. I think it will take about 450 leds for this screen (about 30 x 60 cm). I suppose I could use strip leds and just glue down some rows but I would really like to find a 500 pc bag of smd leds so I can get the most uniform layout.

[cashkennedy]

Re: Eliminating the inverter board

You asked about where to draw power from:

You said this had an inverter board, what voltage is running to that? If its 18v or 24v you would want to draw power from that since it has the amperage necessary since it used to power the ccfl's.

I believe if your installing LED'S if you buy ones with ~ 1.5v drop per LED, then you do 16 of them in series (24v drop total), and then do a lot of the strings of 16 in parralellel you could safely power them from the 24v rail.

Basically with led's you have to be carefull that they have the right voltage across them by either having a lot of them in series , or having resistors (would waste power). Theres some LED calculators online that tell you what resistor to use based on the LED's current / voltage, and your input voltage.

[budm]

Re: Eliminating the inverter board

White LED Vf (Forward Voltage) is 3.4V.
You may want to learn more here:
http://white-leds.co.uk/led-wiring-guide.htm

[tom66]

Re: Eliminating the inverter board

I did this for a 15" LCD monitor.

I replaced them with RC aircraft LED strips rated for 12V. As monitor ran off an 18V plug pack, I used a 27 ohm 5W resistor to drop the voltage. (LEDs drew ~200mA.)

[cashkennedy]

Re: Eliminating the inverter board

Ive only worked with PLCC4 4 color led's which have lower voltages on the red light. And using too large a resistor just makes them dimmer anyway.

But in general you just take the input voltage and devide it by the led's voltage drop to find out how many you can run in series, then possibly use a resistor for fine tuning, and run a bunch of parallel strips of the amount in series you calculated.

So anyway the point is the LED work and running it of the power supply is all very easy to handle. The tricky part is whether the tv will run with the inverter disconnected.