hitachi L40A105E no backlights

[mattstolte]

so I received this tv with no main in it, so I purchased a new main which they only have 1 for this model which I was lucky. and the backlights are not turning on. and it has a ribbon going from the power supply to the main so I don't know how to check the voltages but I checked it at the inverter and it is getting the 24 volts, so I thought maybe it was inverter. so I swapped it with another one I already had and it still didn't work, so is it possible the mains bad? I thought that as long as the 24 volts is going to the inverter that the backlights would be on?

[mattstolte]

Re: hitachi L40A105E no backlights

here is the set up and I even disconnected the cable that goes from top panel from the main and still nothing

[johnboy1313]

Re: hitachi L40A105E no backlights

Check for fuses on the inverter(s). When you find them, check to see if they are good. If they aren't, replace them.

[budm]

Re: hitachi L40A105E no backlights

You have 24VDC for power but do you BL-ON & Dimm control signals from the main board to turn on the inverter circuit?
Is this your inverter board?
http://www.shopjimmy.com/samsung-lj9...-inverter.htm#

[mattstolte]

Re: hitachi L40A105E no backlights

yes bud m it is, and I have 2 inverters both with good fuses. im alittle confused I thought that if there was 24 volts to inverter that it automatically would turn on? so you saying that even if there is 24 volts going to inverter that the main could still be bad? if you look at the set up its a ribbon cable so I don't know how to check for bl on and dim

[budm]

Re: hitachi L40A105E no backlights

"I thought that if there was 24 volts to inverter that it automatically would turn on? so you saying that even if there is 24 volts going to inverter that the main could still be bad?" The inverter has to be able to go off when the TV is in standby mode (not powered off mode) when no Video signal is detected.
If you look at the big white connector, you will see the pinout chart of the connector, you need to check the DCV of the ENA pin, DIM pin, Ex_dim pin with ref to the chassis GND.

[mattstolte]

Re: hitachi L40A105E no backlights

bud there is no labels on the power supply or main

[budm]

Re: hitachi L40A105E no backlights

The large connector (the one that goes to the power supply baord) on the inverter board is the one I am talking about, sorry for not being clear.

[mattstolte]

Re: hitachi L40A105E no backlights

ex dim 3.25
dim 2.75
ena 0
so does that mean bad main since ena is 0? and what is ena? and could I repair something on the main to fix this?

[budm]

Re: hitachi L40A105E no backlights

ENA = Backlights Enable = BL-ON, <1V = OFF, >2.5V = ON. so your main board is not sending out or may be the new main board pinout is not the same as the old board.

[mattstolte]

Re: hitachi L40A105E no backlights

Is there anyway to fix this on the main board

[budm]

Re: hitachi L40A105E no backlights

Do you have service manual that shows all the details schematic of the main board and can you read the schematic in details?

[mattstolte]

Re: hitachi L40A105E no backlights

Do you have service manual that shows all the details schematic of the main board and can you read the schematic in details?

no and no sorry. know do you know if normally it is some surface mount ic or anything? how can I check these ics?

[budm]

Re: hitachi L40A105E no backlights

You need to trace that BL-ON pin on the main board to see where it goes to, probably a switched transistors that get the command signal from the processor, to test the IC or transistor you will need to know what they are by looking at the spec sheet.

[mattstolte]

Re: hitachi L40A105E no backlights

Bud thanks alot I will try to figure it out I'm new to stuff like this but I like learning how this works. I can easily diagnose a tv and swap a board but I wanna learn how to get down to component level and such

[budm]

Re: hitachi L40A105E no backlights

Right now what you can do is to disconnect the ENA pin from the connector, then a 500~1K between the ENA pin on the inverter board and the 5VSTBY pin to force on the backlights so you can see if you do get the pictures on the screen, if not then you have more than one problems on that main board.