Hitachi LE55G508 no backlight

[fcisolutions]

I am able to test both led circuits with a LED tester. Powering the LEDs when the set is on shows an image on the LCD. So even though I'm getting voltage on the power supply, I'm thinking the supply is bad. How can I further test the power supply other than voltage at the connectors? Thanks, Jim

Attached is an image of the power supply:

Voltages
----------
Con1 when on
pin
1 12.47
2 12.47
3 12.47
4 0
5 0
6 0
7 0
8 3.26
9 2.9
10 3.24

Con3a
66v at the led connectors when on

[budm]

Re: Hitachi LE55G508 no backlight

So only one LED connector? You have 4 wires on that LED connector (leave connector in place) so turn the TV OFF, put black probe on the chassis red probe on one of the four LED wire see what DCV you get, then turn on the TV watch the meter to see how high the DCV jumps up to then wait for 3~5 seconds and see how low the DCV will go down to then turn TV OF and do the same test for the other three wires on LED connector. Report the readings.

BTW:
Con1 when on
pin
1 12.47
2 12.47
3 12.47
4 0
5 0
6 0
7 0
8 3.26
9 2.9
10 3.24
Those readings above are not helping much without the pin names to go along with the pin numbers.
We also need to see the whole back side of the TV.

[fcisolutions]

Re: Hitachi LE55G508 no backlight

Thanks budm!! Sorry about the not including the pin names. I'm a newbie here.

Ok when powering on the tv and my meter leads as you outlined here are the results:

LED1+ --- B4-0 ... On 66.2v ... 3-5sec 66.2v
LED2+ --- 0 ... 66.2v 66.2
LED1- --- 0 ... 0 0
LED1- --- 0 0 0


Con1 when on
pin
1:+12v --- 12.47
2:+12v --- 12.47
3:+12v --- 12.47
4:SGND
5:SGND --- 0
6:SGND --- 0
7:SGND --- 0
8:BK/ON --- 3.26
9:PWMDIM -- 2.9
10:PS/ON --- 3.24

[budm]

Re: Hitachi LE55G508 no backlight

BL-ON is present.
Strange thing is that there are two boost converter circuits for two set of LEDs but I see only one LED connector being used.
For 55 INCH TV, I expect BOTH connectors to be used.

[fcisolutions]

Re: Hitachi LE55G508 no backlight

Oh and yes only one led connector. I haven't opened the panel but the the led connector wire is taped and looks intact. Maybe power supply?

[budm]

Re: Hitachi LE55G508 no backlight

OK, I found good pictures of your board at shojimmy.
Hitachi MP165D-1MF24
http://www.shopjimmy.com/hitachi-mp1...er-supply.htm#
The two LED connectors are connected in parallel so there is no problem.
We need the DCV of filter cap C13 by the LED connector, we need to see if it also has about 66VDC at that cap too, if it shows 66VDC too then the boost converters are not working.
What kind of LED tester you have?
Pictures provided by shopjimmy.

[fcisolutions]

Re: Hitachi LE55G508 no backlight

Yes 66v at C13. I bought the LED tester from shopjimmy. Again thanks for your leadership.

[fcisolutions]

Re: Hitachi LE55G508 no backlight

And yes the led tester has the ability to show the total vf so I can compare led strings.

[dskall]

Re: Hitachi LE55G508 no backlight

Are you getting same voltage from your tester and when they are plugged into the board?

[fcisolutions]

Re: Hitachi LE55G508 no backlight

Anything I can do to fix the boost converters or should I purchase a working power supply?

[fcisolutions]

Re: Hitachi LE55G508 no backlight

So I broke down and ordered the power supply and now the tv works. Thanks to budm for leading me on the path to the test of the boost converters. That was definitely the problem and maybe next time we can work on fixing the supply. I appreciate all those that helped or commented on this post.