E321VL Powers Up But Backlight Cuts Off

[1beertap]

Hey Guys, I have this TV that comes on but the backlight will turn off. A flashlight test shows an image on the screen. I can take the third wire from the end called "INV ON/OFF" off of the connector and place it on the pin after the TV is on and the backlight will turn on. Also, I have applied 3.2V to this pin after the TV has been on and got the same results. My voltages are as follows with the TV on:

VBR_B = 1.51V
STATUS = 3.31V
INV ON/OFF = 3.26V
REMOTE ON/OFF = 3.28V
12V = 12.13V
12V = 12.13V
12V = 12.13V
GND = 0V TESTED OK
GND = 0V TESTED OK
GND = 0V TESTED OK
GND = 0V TESTED OK
5.2VSB = 5.25V
5.2VSB = 5.25V
5.2VSB = 5.25V

Any ideas? Thanks.

[tom66]

Re: E321VL Powers Up But Backlight Cuts Off

So the backlight stays on if you wire in the BL ON command HIGH?

[1beertap]

Re: E321VL Powers Up But Backlight Cuts Off

Tom, the thing I don't understand is that the bl_on has 3.26V on it when the termimal is in the connector with the TV on. As I turn the TV on, the backlight comes on briefly and goes out, I disconnect the bl_on terminal and reconnect it and the backlight comes on and stays on, the voltage on this wire stays the same except when the TV is off.

[1beertap]

Re: E321VL Powers Up But Backlight Cuts Off

I think my problem might be a bad controller chip with part number "0Z9977BGN" Its located on the bottom of the power supply board. I've noticed that when everything is connected, upon turning the set on the backlight will dim down, as if a large current draw exist, and then return to full brightness before turning off completely. Also, the INV ON/OFF voltage drops briefly during this time. My meter is not quick enough to see how much voltage drop. I'm wondering that during this brief time the sensing side is telling the microcontroller to shut down the backlights thus having me to manually reinitialize the backlights at a later time to come on. Any thoughts? Thanks.

[1beertap]

Re: E321VL Powers Up But Backlight Cuts Off

I upload a video of what this TV is doing. The link is below.

https://www.youtube.com/watch?v=qwAM...ature=youtu.be

Hopefully, this clear up some confusion. Thanks.

[1beertap]

Re: E321VL Powers Up But Backlight Cuts Off

Question: I found a main board that I would like to try but it has part number 3632-1792-0150 (4F) and my board is a 3632-1792-0150 (4E). I know that the difference is the firmware revision, will this matter? Physically the boards look the same.

[tom66]

Re: E321VL Powers Up But Backlight Cuts Off

Can you try disconnecting VBR_B and connect it to BLON. This will force the backlight to 100%. Some aged CCFLs might not properly light at low intensities.

[1beertap]

Re: E321VL Powers Up But Backlight Cuts Off

I disconnected VBR_B and connected it to BLON. The backlight lit for a few seconds and cut off.

[tom66]

Re: E321VL Powers Up But Backlight Cuts Off

Odd...
If you force BL ON directly it works - but will it work if you leave it for, say, 10 minutes after last starting it?

[1beertap]

Re: E321VL Powers Up But Backlight Cuts Off

Yes, the backlight does cut off after 10 minutes.

[tom66]

Re: E321VL Powers Up But Backlight Cuts Off

So it won't start if left cold for 10 minutes?

[1beertap]

Re: E321VL Powers Up But Backlight Cuts Off

I may have misunderstood you. I forced the BL ON directly, after being on for about 10 minutes the backlight cuts off.

[budm]

Re: E321VL Powers Up But Backlight Cuts Off

It goes off after 10 minutes with video source feeding the TV? it sounds like it goes into standby due to lack of video signals, may be not.

[1beertap]

Re: E321VL Powers Up But Backlight Cuts Off

I connected a video source, then waited 10 minutes and the backlight stays on. You were right about the lack of a video source then going into standby.

[1beertap]

Re: E321VL Powers Up But Backlight Cuts Off

When the backlight comes on for the first time, when turning on the tv, is it supposed to stay on or does it cut off for a second then come back on and stay on? I'm just trying to figure out if the momentary loss in power on the INV_ON/OFF terminal is normal or not. Thanks again.

[tom66]

Re: E321VL Powers Up But Backlight Cuts Off

When the backlight comes on for the first time, when turning on the tv, is it supposed to stay on or does it cut off for a second then come back on and stay on? I'm just trying to figure out if the momentary loss in power on the INV_ON/OFF terminal is normal or not. Thanks again.

I have seen some TVs do this, it appears normal.

[1beertap]

Re: E321VL Powers Up But Backlight Cuts Off

I felt this was normal, is there anything else I can try?

[budm]

Re: E321VL Powers Up But Backlight Cuts Off

Some does that during the start up.

[1beertap]

Re: E321VL Powers Up But Backlight Cuts Off

With everything connected and turned on these are the readings I get at CN201.

VBR_B = 1.51V
STATUS = 3.31V
INV ON/OFF = 3.26V
REMOTE ON/OFF = 3.28V
12V = 12.13V
12V = 12.13V
12V = 12.13V
GND = 0V TESTED OK
GND = 0V TESTED OK
GND = 0V TESTED OK
GND = 0V TESTED OK
5.2VSB = 5.25V
5.2VSB = 5.25V
5.2VSB = 5.25V

What is puzzling to me is the fact that I have all good voltages but the backlight turns off. Again, I can disconnect and reconnect the INV ON/OFF and magically the backlight turns on and stays on until I turn the tv off. Isn't the backlight supposed to come on with 3.26v on the pin? Anyone?

[budm]

Re: E321VL Powers Up But Backlight Cuts Off

That is a strange symptom indeed.