Hitachi LE55A6R9A - No backlight

[attainteddragon]

Re: Hitachi LE55A6R9A - No backlight

i would never recommend that anyone bridge over bad led's, especially on a panel that has obvious led flaws. hang on, you should not do it to any tv no matter what.
you are going to have one string of led's drawing more current than the other and more issues will arise, then you will be opening it up again.

[RCbar2k]

Re: Hitachi LE55A6R9A - No backlight

You are probably right, but with all things it is risk/reward. The TV is 3 years old and this way was free vs. spending $75 to replace the LED strip. If I get 6 months or more out of it, I’ll consider it a win.

[budm]

Re: Hitachi LE55A6R9A - No backlight

You should at least then turn down the backlights level to as low as possible. When you bypass the LED/s the PWM controlled will run hotter to compensate for the bypassed LED.

[Andrew F. Ali]

Re: Hitachi LE55A6R9A - No backlight

Instead of a wire bridge perhaps 2 (two) 1N4007 diodes in series could be used.

[RMBraught]

Re: Hitachi LE55A6R9A - No backlight

I created an account here just to say Thank You to all who have posted in this thread, the information was invaluable (and not readily available anywhere else, free, via GoogleFu.)
..and to report my personal experience; I have a winner!
TL;DR : Screen black, else OK; found one bad back light LED; solder bridged bad LED connections; back lighting restored!
DETAILS: (hopefuly adding some information to what's already been previously posted) As stated, the back light LEDs are all wired in series in this model; 66 of them, 3 volt SMD 3030 type. Two "strings"; upper and lower screen halves; exiting via two 2 wire connectors ending up back at the power supply board (said connectors also wired in series at the board.) Replacement strips are available (it uses 6-6 LED strips and 6-5 LED strips) but a full set currently runs ~$50-70. I was NOT going to invest for resale/rehome at that price; I got the set free, as-is, from a neighbor and already have enough flat screens for my purposes.
There's an excellent disassembly/repair video by ShopJimmy on YouTube showing the steps involved to get to the LED strips. I *did* invest in the two suction cups as shown in the video (to be able to lift out the screen easily w/o damage); got them from Lowes local for $7 each (my only expenditure for this repair; new tools I get to keep!)
I *individually* tested each LED; there are pads on the component (up) side of the strips next to each back light LED to allow you to do this. I used a 9 volt battery in series with a 5K ohm resistor (a 4.7K ohm would work) and one by one verified each to illuminate (polarity *is* important with this test, + to +, the strips are marked.) Alternatively I later discovered my older Beckman digital multimeter on diode test would accomplish the same thing (although in my experience, a meter's diode test isn't necessarily guaranteed to light up a LED.) Note: My bad LED did *not* look "burnt", even under magnification; I wouldn't have been able to do a passive visual diagnosis.
I popped off the clear plastic dome for the bad LED with a miniature screwdriver and discarded it. I *tried* to use hot air desoldering to remove the offender (without prying the strip out, held in by "very strong" double sided tape) but it chipped off anyway during handling, leaving me with the two tinned pads (internal to the LED.) Small solder blob bridged the two pads.
Addressing the concern for this "modification": math tells us yes if a fixed voltage is feeding the string the current would go up *but it's only a 1.5% change* for a fixed voltage (66 LEDs down to 65 LEDs.) Alternatively, if this design is using a *current* regulated supply (I don't know) *no change would occur at all* (in my experience with optical laser LEDs a supply may be designed for current regulation, not voltage.)
I did decrease the "back light" setting down to "80" (as received, was set to "100". Default?) to hedge the bet.
So far no one can tell me where the burnt out LED "is"(was.) FWIW fifth row, right of center.
The only "casualty" from open to close was the primary white reflector sheet (with the LED holes cut out to peek through), when I was pulling it off it started to split in the middle. I used packing tape on the back side to patch the tear; no foul, good to go. Also minor nuisance: a small black fleck appeared between the back sdie of the screen, in front of the deflector sheets after reassembly (although I worked with canned air to keep dog hair etc from accumulating while the screen/diffusers were out.) This was immediately apparent on power on (a 1/8" black spot.) It started toward the top in the middle, obviously loose (dropped a bit during handling.) I took out the frame screws at the top, and partially down both sides; pulled the frame off to loosen the "sandwich"; the black fleck fell the rest of the way down to the bottom (I was prepared to try to "blow it out" w/canned air but didn't need to.)
That's a wrap. Thanks again!

[dragonmas]

Re: Hitachi LE55A6R9A - No backlight

Well second LE55A69A bit the black screen bullet.(no backlight) ordered a SID GJ2C tester.
Broke down the TV and found 1 short side(side with power connector) strip no leds lighting up. Replaced all strips and tested at the power connector of each individual strip. All good. Re assembled TV. Still no back lights. Checked CN202 Red=271vDC White=190VDc
CN203 Red=190vDC Black=0.Inject 325vDC from tester to CN202, Red lead to red wire, black lead to white. 325 drops to 88.8 and get light. Inject same to CN203 325vDC no change no light. Still had extra power supply and main board ordered for 1st tv repair. Same results. Voltages from both power supplies and main boards same.12-12-12-0-0-0-0-3.1-3.1-3.1 from PS to main board CN201 to Con801 and 5vDC pin 8 Con 901.
Question? Should there have been a change(lights)when injecting CN203 output wires. If so does it seem an open in wire from CN203 to led strips. Or could be T-Con.
Thanks

[dkneyle]

Re: Hitachi LE55A6R9A - No backlight

Sounds very much like an open circuit there somewhere. If you are using your LED tester to inject voltage and the LED string isn't lighting, then it seems there isnt much else it could be???

[dragonmas]

Re: Hitachi LE55A6R9A - No backlight

One of the connectors on the red/black string didn't seat correctly. Now I have all backlights on.CN202 has 202vdc on red and 101vdc on white.CN203 has 101 on the red and 0 on the black. I was very careful removing the screen both times and used suction cups but now I think my screen is screwed. I have all the correct voltages from the PS to the main board and have swapped out PS, main and Tcon and get a display that is whacked. See .jpg. Is this a whacked screen?

[diif]

Re: Hitachi LE55A6R9A - No backlight

Sadly, yes, a damaged panel. You can see blue, top right where the black and white meet the edge.

[dragonmas]

Re: Hitachi LE55A6R9A - No backlight

Well at least now I have 2 sets of parts.

[dkneyle]

Re: Hitachi LE55A6R9A - No backlight

How sad. Yep, strip for parts and advertise for sale. You know all boards are in working condition.