Chosen Solution
My Philips BDM4065UC suddenly stopped working recently. The issue seems to be only the backlight - the USB hub works, the standby light works, the menu joystick correctly resumes from power off, and with a bright flashlight I can see the expected picture on the screen. When first powering on, the backlight comes on at full strength to show the blue Philips logo, very quickly dims to about half brightness, then shuts off completely. The center row appears to dim more than the edge rows. Power Board:
I’ve disassembled the monitor to attempt a diagnosis. The connection to the mainboard seems fine - the 19V pins all supply ~20.2V, the 5V pins are at ~5.5V, and the ON/OFF and DIM pins have 3.3v on them during operation. Mainboard pins:
The LED output pins seem questionable. The pins are labeled LED +V and LED-V, without saying what those voltages should be. There are 4 pins (leading to 4 rows of LEDs), each of which show 11.5V in operation - both during the initial period of backlight ON, and after it shuts off. The return lines are combined, and show some variation - during initial backlight ON period, they show up to 45V (approximately the outgoing voltage for all four LED strips). After the backlight stops working, they show ~30V. LED pins:
Is this a power board issue? Or should I be looking downstream at the LED strips? There was no brightness problems before the sudden onset of this problem, but there is a bit of variation in how the strips behave currently.
Hi @flowmage , I don’t know but a quick way to test the backlights without disassembling the screen, is to use a TV backlight tester (supplier example only) to test each backlight strip individually. Disconnect the LED power cable from the power board and hook up the tester to the cable. It supplies the necessary power for each strip (one at a time) i.e. no power required to be connected to the monitor, so that you can see if there is a problem or not. If all the strips are OK then you know that the problem is elsewhere. If the strips are the problem then here’s a link regarding the LED strips for your model that may be of interest
