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| Putting a monitor to sleep when no video signal |
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| tom66:
You will discover with LED TV backlights if you simply break the circuit that is used to power the LED array, in most cases the LED driver will go into a fault state and power will not resume after the connection is restored. They have a maximum open circuit voltage (as they are constant-current type) but will go to a fault state once this is reached. If you can isolate the 12V/24V to the backlight controller that might work better. I didn't see many of these drivers that reported the fault state back to the TV, so I imagine that would work ok. But many times the backlight driver is built directly into the PSU or main board. |
| soldar:
Yes, the reason I thought about this is that i have been dealing with different LED drivers recently. I have a thread in Repair about a large TV https://www.eevblog.com/forum/repair/philips-47-tv-47pfh410988-repair/ And, also about two or three years back I bought a bunch of LED ceiling fixtures and they have been failing one after another and I had a look at the driver and found they are putting too much current through the LEDs. No wonder they are so bright! One of my pending projects is to install a resistor in parallel with the LED strip so it will shunt some current away. And, yes, I am thinking preferably in terms of disabling the backlight supply, not just disconnecting the LED load. |
| tom66:
Looking quickly at your model it appears to be an OEM Vestel clone (I fixed so many of these when I was a student). They use a BL_ON signal on the pin from the main board to PSU which is just 3.3V CMOS. Modifying that is trivial. There is also a PWM signal, but I'm reasonably sure that it does nothing if BL_ON is low. Schematics for both power and main board are usually available with a bit of searching. Vestel tends to use "17IPS" or "17PW" part number prefix for their power supplies and "17MB" for the main boards. You might also be able to root the operating system pretty easily to control whatever you want, I did that on a UMC TV (Slovakian vendor of many TVs), I upgraded the bootloader to put a logo of my cat on power on, because well, why not? ;D Vestel don't make monitors (AFAIK) but it might be that you can force a HDMI input into PC mode or just control the PWM over Ethernet/USB if the TV has such ports. |
| soldar:
--- Quote from: tom66 on February 07, 2024, 03:42:47 pm --- Looking quickly at your model it appears to be an OEM Vestel clone (I fixed so many of these when I was a student). They use a BL_ON signal on the pin from the main board to PSU which is just 3.3V CMOS. Modifying that is trivial. There is also a PWM signal, but I'm reasonably sure that it does nothing if BL_ON is low. Schematics for both power and main board are usually available with a bit of searching. Vestel tends to use "17IPS" or "17PW" part number prefix for their power supplies and "17MB" for the main boards. You might also be able to root the operating system pretty easily to control whatever you want, I did that on a UMC TV (Slovakian vendor of many TVs), I upgraded the bootloader to put a logo of my cat on power on, because well, why not? ;D Vestel don't make monitors (AFAIK) but it might be that you can force a HDMI input into PC mode or just control the PWM over Ethernet/USB if the TV has such ports. --- End quote --- Thanks. That is very enticing. I am definitely not going to get into the OS because it just is not worth it for me but hijacking the BL_ON signal seems like a very practical way to do it. The only issue is that the monitor is in use and I would rather not mess with it while I need it. I will have to find the right moment to open it up but this line looks promising. And, frankly, I should have thought of it myself because i have seen this signal in other screens. I will see if I can find the schematic. Thanks. |
| soldar:
I have found this image of what I think is the PSU. I assume the AC mains power comes in at the top left white connector, The LED power goes out the upper right white connector and the bottom right, black connector takes the power to the main board and receives the disable signal. Edit: I found the schematic and it looks like pin 3 of the connector is the standby signal but I cannot read the labels well. |
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