Hitachi LE55A6R9A - No backlight

[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

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

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

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

[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

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

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.

[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

[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.

[dskall]

Re: Hitachi LE55A6R9A - No backlight

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

[attainteddragon]

Re: Hitachi LE55A6R9A - No backlight

anyone near him want an easy tv for repair!

[Tron guy]

Re: Hitachi LE55A6R9A - No backlight

Just bridge the connections

yeah if that had even a 1% chance of working I'd do it.

I am at work not at home where I have complete access to my work bench and all of my tools. I've done some pretty intricate soldering before and I don't believe I could pull this off if I had my tools at my disposal.

I love this site and I appreciate the insight, I probably won't be back because I don't intend to work on this type of tv ever again.

thanks guys

[dskall]

Re: Hitachi LE55A6R9A - No backlight

Just bridge the connections

[Tron guy]

Re: Hitachi LE55A6R9A - No backlight

well I got everything apart , started to install the new led strips and the busted at the connection between the 2 pieces.

I call shopjimmy and they said "yeah, manufacturing defect"

This thing is apart and at work and in the way. So in the trash it goes. oh well

[Tron guy]

Re: Hitachi LE55A6R9A - No backlight

Well just following up on this one. Shopjimmy just got the led strips back in stock, so now I have them.

This is my first lcd/led tv repair, I've done hundreds of crt's. I have to say, this reflector shield or whatever they call it is a joke. It's paper thin and it's held down with double sided tape. I will report back with how much damage I do to it and also if changing the led strips fix my problem.

[Tron guy]

Re: Hitachi LE55A6R9A - No backlight

Thanks gentlemen.

I think I replied earlier without reading all of recent replies to this thread.

Looks like I should learn how to carefully open this thing up and pull out my meter and look for a break in continuity.

It sounds like maybe I should do it with the power on as well and see if the voltage stops somewhere along the line?

[dick_barton]

Re: Hitachi LE55A6R9A - No backlight

It's a large screen so I would search the forum for information on hints and tips for lifting away such a large lcd panel without breaking it.
There are also "Youtube video's" which could aid you. There are also a lot of useful tips for testing the leds.

[Tron guy]

Re: Hitachi LE55A6R9A - No backlight

The leds are connected in series, a little like old fashioned fairy lights, and when one goes open then no current can flow in the circuit to light the leds.

On the other hand it could be that a connection on the led strips inside the panel has gone open and that would cause the same fault condition. This has been the case in other threads here on the Forum where wire has been soldered across the connection to bridge the fault out.

So I could pull the panel open and look for continuity from the begging of the wiring to the end of the led strips? Somewhere in the middle there may be a loss of connection?

Or do I just buy the led strips (when they become available again from shopjimmy, unless someone knows elsewhere to buy them), and change them?

[dick_barton]

Re: Hitachi LE55A6R9A - No backlight

The leds are connected in series, a little like old fashioned fairy lights, and when one goes open then no current can flow in the circuit to light the leds.

On the other hand it could be that a connection on the led strips inside the panel has gone open and that would cause the same fault condition. This has been the case in other threads here on the Forum where wire has been soldered across the connection to bridge the fault out.

[heavymachines]

Re: Hitachi LE55A6R9A - No backlight

i believe it works like this....If you have a very high voltage spike going to leds then that is a very strong indication there is an open led because it won't turn on to draw that power to put a load on it and draw to normal voltage ranges approx 1XX volts. When power supply detects this over spike high voltage it goes into protect mode and shuts it down due to open (blown) leds.