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Got this older Philips 26PF5321 LCD-TV, like it because it is not a smart-tv.

Philips 26PF5321

What I dislike about this TV is the fixed backlight setting (cannot change it via software menu and there is no update for that setting). It doesn't change when you change the brightness for example. Watching a movie or playing a game in a dark room is not a pleasure (very, very bright and black is very soft gray) so I want to do something about it.

There is an inverter board inside that drives the background light bulbs. Do you think it is possible to control the voltage to this board to make it possible to control the brightness or is this, in basic, just a silly/stupid idea?

Didn't open the TV yet so I don't know how it is exactly organized. I expect that it is controlled by one or two boards that drive an array of bulbs, like many LED TV's of that era (2006).

I think, the easiest way to do this is to 'manage' the input voltage to the inverter (expecting it is a lower voltage than the high voltage output to the bulbs) but don't know how the inverter will react by doing that. Some people got any experience with this?

Here is the specs of the TV:

http://www.p4c.philips.com/cgi-bin/cpindex.pl?scy=PL&slg=EN&ctn=26PF5321/12

https://www.scribd.com/doc/17746102/Philips-Chassis-Lc4-31-ET

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    \$\begingroup\$ it says in the leaflet that the backlight is dimmed to increase contrast (presumably when the whole picture is dim) so you need to find out how the backlight dimming is commanded and subvert that. possibly one of the wires to each inverter carries a DC signal... \$\endgroup\$ – Jasen Mar 28 '17 at 5:31
  • \$\begingroup\$ @Jasen: Thanks for the comment. There is no dimming at all (or maybe not working?). I think, the Philips Chassis schematics are of all possible models / variations of models. Maybe it is not elegant but before I open the TV i want to know it is possible limit the input voltage without negative sideeffects (malfunctioning). \$\endgroup\$ – Codebeat Mar 28 '17 at 20:16
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enter image description here

Arrows indicate direction of voltage for "more dimming" with current controlled by voltage drop across twin R's 2R2 from 5.2V. It should be controlled by remote Brilliance on screen and Light Sensor. But this is a more direct way .

Monitor voltage on test points 1094, 1040, 1038 if you need help choosing an R value and report back.

Then contrast can be increased on display to adjust black level as full black.

There are better ways, but more complex.

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  • \$\begingroup\$ Thanks for the answer! There are not easier ways to do it? Just limit input voltage of the board? Or, when I do this, will it have strange side effects except dimming? \$\endgroup\$ – Codebeat Mar 28 '17 at 20:21
  • \$\begingroup\$ Q7092 may use PWM to control brightness while Q7030-b results in voltage control of LED current. This is controlled by R ratio of R3032(-) /R3031(+) . to make dimmer adjust R in direction of polarity to raise voltage. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 28 '17 at 20:33

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