Hitachi LE55A6R9A - No backlight

[attainteddragon]

Re: Hitachi LE55A6R9A - No backlight

anyone near him want an easy tv for repair!

[dskall]

Re: Hitachi LE55A6R9A - No backlight

Well I'm only couple hundred miles away, but I get mine without driving very far.

[Mcclmark]

I have this same tv. There are 2 led series wires going to the small connectors with the white,red and black,red wires. One set of wires for the top of panel, one bottom of panel. The outermost pins on the 2 connectors provide the voltage while the 2 inner jumper the led series together.

Probe the 2 outer pins with a multimeter on DC volts. You should see over 200 volts if the led driver is working. This means an led blew and created an open circuit.

Optional... You can short the pins on either connector while hot and figure out which connector of leds is bad... The backlight will come on. Shorting the connector essentially removes one set of leds from the entire series.

If the driver is working and the backlight enable pin (labeled on board) shows around 3.3 volts the driver is fine and it is the LEDs.

Be extremely careful removing the black strip clips holding the glass, note carefully how they come off for reassembly.

Peel the screen apart so you can gain access to the LEDs... Do NOT remove the white paper like backing.

Identify the bad LED... It will look charred and black. Pop the lens and use a pliers to break it off down to the solder pad. Use foil and tape or preferably add a solder blob over the bad LED solder pads to short them together. Use continuity setting on multimeter on nearby +- pads to check the intensional short.

You won't notice a few LEDs missing... Don't spend money on replacement boards.

Carefully reassemble... The LCD is very easy to crack.

[dragonmas]

Re: Hitachi LE55A6R9A - No backlight

Does anyone know what the correct voltages are at the diodes DH7 and DH8? I get about 257Vdc with and without the backlight leads connected. Also get 257VDC at CN202 and 0 at CN203.Same model TV, Black screen. Meter reads correct(Fluke DVM) and has new leads. All voltages from the control board are correct to the PSB.
Thanks

[budm]

Re: Hitachi LE55A6R9A - No backlight

Does anyone know what the correct voltages are at the diodes DH7 and DH8? I get about 257Vdc with and without the backlight leads connected. Also get 257VDC at CN202 and 0 at CN203.Same model TV, Black screen. Meter reads correct(Fluke DVM) and has new leads. All voltages from the control board are correct to the PSB.
Thanks

The boost converter circuit is working, what you need to do to find if the LED strings have open circuit or not is to:
1) Turn the TV off, all connectors back in place.
2) Leave black probe of the meter on the chassis.
3) Put read probe on the Red wire of the LED connector (the one with RED/WHITE WIRES, you will need skinny probe to probe from the wire entrance side of the connector.
4) Turn the TV on to see how high the Voltage jump up too and wait 5 seconds to see how low it goes down too, report that reading.
5) Repeat step 3 on the OTHER 3 wires of the LED connectors.

[richten]

Re: Hitachi LE55A6R9A - No backlight

Pardon me if this isn't proper forum etiquette to post this here...

I also have a Hitatchi LE55A6R9A wtih no video/backlight after possible power surge. Power light is on & TV passes flashlight test. All LED strips were replaced with new ones (from ShopJimmy) less than 90 days ago after i lost the backlights.

Surely the LED strips dont need to be replaced again....I was able to replace them myself without too much issue before. However, I dont have much experience testing components with a multimeter, so troubleshooting this issue is tough for me. Is it possible one of the boards, main, t-con, or power supply, is bad due the power surge? Even though it passes the flashlight test...

I know the board replacements would be fairly easy, but I dont really want to go thru the LED strip replacements again....

Any advice would be greatly appreciated here.

Thanks
Richie

[budm]

Re: Hitachi LE55A6R9A - No backlight

I am a little confused, you indicated that there no video/backlights but it passes the flashlights test so you do have pictures then and can be seen with the flashlights?

[richten]

Re: Hitachi LE55A6R9A - No backlight

Sorry for the confusion....Yes...I can see the picture when shining a flashlight thru the back.

[budm]

Re: Hitachi LE55A6R9A - No backlight

So the T-CON and main board are at least working in the Video section then. You just have to test the Voltages at the LED connectors per post #45.

[richten]

Re: Hitachi LE55A6R9A - No backlight

So the T-CON and main board are at least working in the Video section then. You just have to test the Voltages at the LED connectors per post #45.

Ok, so before I go tearing into the TV again, what are the possible causes here? If there is an open circuit, would that be due to a single bad LED strip? Or is there another cause for this type of issue? Just trying to determine what I'm up against...

[budm]

Re: Hitachi LE55A6R9A - No backlight

No need to tear the panel apart yet until you provide us the Voltage readings.
BTW, did you turn the backlights down as low as possible on all input setting?

[richten]

Re: Hitachi LE55A6R9A - No backlight

No need to tear the panel apart yet until you provide us the Voltage readings.
BTW, did you turn the backlights down as low as possible on all input setting?

Ok, finally got around to testing the voltage at the LED connectors. I get a reading of 272 on the RED from the RED/WHITE pair. However, I am unable to get a reading of anything >1 on any of the other 3 wires. Am I doing something incorrectly with my multimeter or does this indicate a problem with the board? Also, I have not done anything with the backlight level.

[budm]

Re: Hitachi LE55A6R9A - No backlight

You will use chassis GND as the GND ref for each LED wire.

[richten]

Re: Hitachi LE55A6R9A - No backlight

You will use chassis GND as the GND ref for each LED wire.

I did have the black probe on the chassis when testing.

[budm]

Re: Hitachi LE55A6R9A - No backlight

You have open circuit in the LED strings some where.

[richten]

Re: Hitachi LE55A6R9A - No backlight

You have open circuit in the LED strings some where.

So does that mean a bad LED strip?

[budm]

Re: Hitachi LE55A6R9A - No backlight

Bad LED, or connector, or the wiring.
They are all connected in series so it will only take one open circuit to cause the problem.

[RCbar2k]

Re: Hitachi LE55A6R9A - No backlight

Same TV and I am trying to confirm my problem is with the LED strip. I have audio and can see picture with a flashlight. I get 272V at red and 189V at black on RED/BLACK pair (CN202) and then 189V on red and 0 on white on RED/WHITE pair (CN203). Is this an open circuit problem as cited above or a problem with the driver? Thanks in advance.

[attainteddragon]

Re: Hitachi LE55A6R9A - No backlight

if you are measuring in reference to chassis ground, then you have an open led/led's in the backlights. you will need to open the set up (screen removal) to repair.

[RCbar2k]

Re: Hitachi LE55A6R9A - No backlight

Thanks. I appreciate your response. I ended up taking the screen off and found the problem LED by checking each strip using the homebuilt LED checker shown on YouTube (3 9V batteries connected and a couple of wires) at the +- pad at the beginning of each strip. Then I checked each LED individually on the problem strip using the +- pad on each side of the individual LEDs and 1 9V battery (used the battery throwing off the least amount of voltage, like 6ish) to isolate the problem LED (it wasn't obvious on mine, as it wasn't burned or charred). Then I followed the suggestion in Post #43 and removed the LED all the way down to the sodder pad and taped foil across (FYI for those who aren't aware - the sodder pad is two small pieces, a square and a smaller rectangle. It is not one solid metal square, that is the base of the LED light). Plugged it in and turned it on and the backlight lit right up.

Now I just have to put it back together...