TideLog Posts Tagged “screen dim”

I repaired a Luxor LUX-19-822-COB 19″ TV/DVD Combi unit for Greg’s aunt and uncle recently. It is a Vestel, and uses both a 17IPS16-4 combined PSU/Inverter unit and a 17MB46 mainboard. According to Greg, and his aunt & uncle, there was no sound or picture. It turned out there was sound and picture, but no backlight. Inserting a DVD made the TV start the DVD software, and the DVD began playing. There was sound and a faint picture on the screen. All voltages coming out of the PPSU section were present and stable, the TV was running quite happily, albeit with no backlight.

So the power supply was sitting in standby, all main voltages off. Pressing the Power button was bringing the PSU into full On mode, and the voltages were nice and stable, as they should be. This proved the TV’s MCU was interpreting the ON signal and pulling the PS_ON pin high, and the PSU was starting correctly. The DVD module would have shown if there was any failure on the voltage lines as it wouldn’t have accepted the disc, and would have been sluggish or appear dead. The TV wouldn’t have even booted to the DVD Software if the drive wouldn’t start, which I believe is stored on the DVD drive’s Micron EEPROM on these drives, it isn’t part of the TV mainboard.

Vestel-17IPS16-4-PSU

I connected two laptop backlights to it, they flickered then went out, there was no “2 seconds to black” symptom, or red tinge, it was a “blink-and-you’ll-miss-it” scenario. Connecting the TV’s screen lamps up to a laptop inverter revealed they were fine, with no ignition lag or red/pink tinge, so my diagnosis had narrowed the fault down to the Inverter/PPSU unit. Due to not having my oscilloscope or capacitor tester handy, I ordered a new PSU/inverter board, which will be fitted soon. I don’t know what the actual fault is with the original supply, but I will be repairing and re-using it. I’ll update this post when I do repair it. Here’s the TV with the cover removed, you can see how it all fits together:

Luxor LUX-19-822-COB-cover-removed

Another PSU/inverter combi unit that made life easier for me, due to it not doing the protection shutdown feature of separate inverters, where the inverter sends a signal to the TV’s MCU that it has a fault, this then causes the MCU to either not start the TV fully to software boot stage, or to shut down into protection mode if started. Combi PSU/Inverter units do make diagnostics easier, as the TV still starts if the inverter, well, doesn’t 🙂 If the whole TV doesn’t start, the PSU section needs to be looked at, you might have flaky fluctuating voltages coming out of PL804, the L shaped section of pins that connect to the mainboard. Here’s an image I made showing the pinouts of the 17IPS16 connector, the mainboard connector, and the DVD module connector, click it to view it full size:

Vestel17IPS16 PSU Voltage schematics pinoutPlease note, this is my image, I created it using a schematics drawing program, so please don’t distribute it. If you reference it on a forum, please link to it, don’t copy it or modify it.

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