fix lcd no power problem philips 170B systematically
Blank Screen Philips Monitor
A customer put a 17” lcd monitor in my PC repair shop last weekend. The indication of the monitor is no power and blank screen even though the external power supply is plugged in. After I have listened to his words, I do a quick test on the monitor in front of him to double-check the problem. Exactly, the monitor has no led power lit when switch on the power supply. He requests me to repair the monitor as soon as possible because this monitor brings him lots of winning on stock trading. He wishes to use the same setting so that he can win the trade in the stock market. I reply to him confidently that he will be able to receive his monitor next 2 days or early. Then, he walks away happily.
how to analyze and repair LCD monitor no power in simple and quick way
Why am I having such confident promising the customer? Because, I have similar experience on the same model of the monitor and good understanding of circuit operation especially on the switching mode power supply. There is a systematical method I will tell you right here on how to analyze and repair LCD monitor no power in simple and quick way.
Is the fuse blown?
Immediately, I unscrew the outer and inner covers of LCD monitor. Please ensure no power connected to the monitor. The first place to be checked is on the power supply board. I measure the continuity of the fuse 1103 and 9101. Both of them are in good resistance. After that, I inspect all capacitors, resistors, inductors, diodes and ICs are in good shape.
For a quick test, I plug in the power cord and switch on the monitor to do the voltage testing. I use the voltmeter to measure the 12 Vdc output of the secondary transformer 5103. Guess what do I find out? No DC voltage is measured right here. This means the primary section of transformer is not functioning which there is no pulse is provided by the power IC 7101 to the transistor 7102 and followed by the rapid switching of the transistor to induce the transformer 5103 in normal operating condition. This rapid switching of transistor 7102 will produce a stable voltage to Main Controller and other circuits, is rectified and filtered by the diode 1115 and capacitors 2116/2117 on the secondary side of the transformer 5103. I guess a high probability fault on primary circuit of power supply board.
Download the guide on the theory of the switched mode power supply for your reference. Click here Guide on the theory of Switched Mode Power Supply.
Now, I will check two important voltage test points on the primary circuit which are the big filtered capacitor 2106 and Power IC 7101, pin 1. I got reading 300 Volts on 2106 in good condition but the input voltage to IC 7101 pin 1 is 6 volts only. In normal operating condition of IC 7101, the input voltage must be at least 11 Volts or above to start up and oscillate itself internally. Then, I trace the line of pin 1 all the ways up to diode 6102 and resistors 3137/ 3138 which step down 220 Vac to 16 Vdc. Surprisingly, the voltage across the resistors has fallen to half value of 16Vdc. I switch off the power supply immediately and de-solder the resistors and diode from the circuit board. I got the resistance value changed to 1600K ohms each resistors and the diode is ok.
According to Ohm law, the resistance that increases will result the voltage drop. I have the spare resistors and replace the resistors in same specification properly. Within my expectation, the LCD monitor now is returned to normal condition. I leave it run for few hours. Finally, I call the customer to collect the monitor next morning. He receives the monitor happily and gives his appreciation to me.
The whole process of the testing and replacement is only taking 1 hour approximately. I can earn 100 dollar in the short period based on my experience and good knowledge of the working principle on LCD monitors. Now, you can grab this opportunity to learn the systematical method from this book which compiles a step-by-step and head-to-toe practical guidance in photos for smps repairing of LCD monitors. You too can become a professional repairer and earn lots of money from this kind of repair. Click this link to view for further information on the book.
