back light too bright sanyo dp46848

[tvtanner]

I'M WORKING ON 46INCH SANYO AND TOO BRING YOU UP TO DATE. I HAVE PICTURE AND SOUND BUT PICT. IS TOO BRIGHT. LOOKS LIKE THE BACK LIGHTS ARE TOO BRIGHT. REMOTE WORKS ALL ADJUSTMENTS BUT DON'T HAVE MUCH EFFECT BECAUSE OF BRIGHTNESS. ALL POWER SUPPLY VOLTAGES SEEM TO BE NORMAL. I TEND TO THINK ITS BAD INVERTER PANEL BUT I'M NOT SURE. tHE BL-ON VOLT READS 2.6 AND BL-DIM READS 2.4. I'M NOT SURE THIS IS NORMAL. A SCHEMATIC WOULD SURE BE NICE. DOES ANYONE KNOW WHERE I CAN FIND ONE? AS I REMEMBER THESE SANYO'S HAVE A HISTORY OF BAD RIBBON CONN. BUT THIS ONE HAS NO BAD SHADOWS OR ANY THING AND THE SCREEN IS PERFECTLY WHITE WITHOUT SIGNAL. ANY HELP WOULD BE APPRECIATED .

[budm]

Re: back light too bright sanyo dp46848

Do you mean washed out pictures? Please Upload the screen shot.

[Ltank]

Re: back light too bright sanyo dp46848

If the main board Dim command is off try a potentiometer connected as a rheostat until you get the desired results. Measure the resistance then substitute it with a resistor

[tvtanner]

Re: back light too bright sanyo dp46848

Thanks -Good idea . I will try that tomorrow.

[budm]

Re: back light too bright sanyo dp46848

If the Dimming signal is analog, then the dimming signal will be between 1~5V range, if it is PWM then the pulse width will be between 10% (min brightness)~90% (max brightness). So you need to find out if the dimming signal is analog or PWM first.
Can you see the BL_DIM Voltage change when you adjust the backlights?

[tom66]

Re: back light too bright sanyo dp46848

It would require an enormous amount of light (and power) to over-drive an LCD panel so that the backlight looked too bright, more likely it is T-con/Gamma/Panel fault IMHO.

[tvtanner]

Re: back light too bright sanyo dp46848

Back again. I tried decreasing resistance on dim conn. And it did decrease brightness a little but it didn't help. I think after taking closer look it may be contrast problem and as was mention it is a little negative looking and washed out. All controls and voltages check ok as far as i can tell. Picture is too light to show up on camera in order to upload but to me it looks like an old picture tube that is weak when brightness is turned up. How can i be sure its t-con or main board? Any ideas

[tom66]

Re: back light too bright sanyo dp46848

Can you post a picture of the T-con... there is a simple test you can do.

[tvtanner]

Re: back light too bright sanyo dp46848

Will do shortly- i do have washed out pict. What button do i push to get it on line. I haven't uploaded one yet?

[tom66]

Re: back light too bright sanyo dp46848

Below the post area there's a button marked Manage Attachments, that will let you select a file from your computer to upload to the forum.

[tvtanner]

Re: back light too bright sanyo dp46848

Thanks i just got it. Take a look. I did't think it would show up but it did.

[budm]

Re: back light too bright sanyo dp46848

That is what I thought, bad Gamma voltages, washed out pictures.

[tvtanner]

Re: back light too bright sanyo dp46848

Thanks -are you saying its most likely t- con panel?

[tom66]

Re: back light too bright sanyo dp46848

Most likely T-con, a quick check of the gamma voltages can confirm for sure.

[tvtanner]

Re: back light too bright sanyo dp46848

Back with you. Heres picture of t-con panel. Can you tell me if there is any way i can tell if this panel is ok? Where do i check the gamma voltages?

[tom66]

Re: back light too bright sanyo dp46848

Ok along the bottom left of the board (in that photo) you will see a row of points marked VGAMA1, VGAMA2, all the way up to VGAMA22.

You should set your multimeter to the 20V DC scale, place the black probe on the chassis, and touch the red probe on each test point. The set must be turned on and showing a picture. Tell us what you measure on all 22 points, we need results like this:

VGAMA1 - 0.99V
VGAMA2 - 1.32V
...
VGAMA22 - 14.83V

Once you have those numbers we'll be able to tell if the gamma voltages are good or bad, I expect them to be bad in which case you will have to repair or replace the T-con board. Repair is a fairly involved soldering job, but is the cheapest option, it will require replacement of AS15 chip just above those test points. Replacement is easy enough but the board is likely to be somewhat expensive, as this is a common fault affecting these T-con boards.

It's a good idea to install the screws in the T-con if you've removed the shielding over it, so you don't lose them and so it makes it easier while testing.

[tvtanner]

Re: back light too bright sanyo dp46848

Thanks-I should be able to do that Monday . I will let you know

[Alastair E]

Re: back light too bright sanyo dp46848

AS-15 stuffed, 10-1!

[tvtanner]

Re: back light too bright sanyo dp46848

Heres voltage readings on t-con panel. What do you think? taken with on screen.

[tom66]

Re: back light too bright sanyo dp46848

The results indicate the AS15 chip on your T-con board is bad.
You can either replace T-con or if you have good soldering skills you can replace the AS15 chip (about $3 for one)