Hello everyone,
I am a hobbyist in electronics, my neighbour has an LCD monitor of make ZENITH (Indian Company) bought back in 2008, the problem with the LCD is the display goes dimmer & dimmer until he cannot see anything on the screen this has been happening for last 2 weeks now, he turned off the computer and after some time when he turned it on the LCD used to work, Now there is no picture on the screen but the power led is glowing. I connected my LCD screen to his computer to see if the fault is with the monitor or the CPU and my monitor is working giving clear display. So the faulty is with his LCD monitor
When I opened the monitor i checked the inverter board & main board there was no sign of any burnt components both boards were clean.
Then I connected it to the mains AC and checked the output voltages in circle marked 1 it gave 12v & 5v DC for the main board then I checked the voltage in circle marked 2 it gave me 14v AC for the LCD backlight,
then the backlight was glowing and giving me display, so i thought it was a loose connection so I turned off the monitor and after 15 mins I turned it back on (my PC was on) now it was not giving any display and the backlight was not glowing then I checked output voltage at circle marked 2 now it was not giving any voltage. then I disconnected the main board, backlight from the power supply and checked the voltages it was giving output of 12v & 5v DC but was not giving any voltage for the backlight of the LCD (Circle no 2).
The LCD panel is made by LG Philips model - LG LP171WE2
Power board is - HKC pi560
it was assembled for Zenith Computers (India) model - Z787
Then I googled and found some articles online for inverter board testing, most of them suggested to check the inverter transformer (circle No. 4) and transistors near the transformer, to check the feedback circuit, so I removed the Schottky barrier diodes (2 Nos) circle no. 3, part no - SBLF10100CT (attached datasheet as this is the only website providing me the information as google suggested me equivalent MBR10100CT with same as SBLF10100CT). They are Common-Cathode High Voltage Schottky Rectifier Diodes, I checked with my DMM - diode function they tested out fine.
Kindly help me troubleshooting this monitor display problem. I have checked all the capacitors with ESR meter they all are good.
PS - sorry for such a long post, the image of the inverter board is of the same model from internet as I didn't have camera with to take picture.