How To Repair ACER AL712 LCD Monitor With Display Shutdown Problem

This ACER AL712 LCD Monitor came in with the complaint of display shutdown in less than few seconds. Well, I love to repair this kind of problem. Whenever LCD Monitor display shutdown, it can be cause by few reasons, a defective lamp, dry joints in inverter area, bad electrolytic capacitors in the filter lines, capacitance value out in the tuning capacitor, faulty ballast capacitor, defective inverter IC, bad components surrounding the inverter IC area, faulty start circuit, a missing “ON” signal from the main board/AD/logic board or even a defect in one of the push pull pair transistor (bipolar or FET transistor).

After the cover and the internal metal were removed I saw two electrolytic capacitors located nearby the high voltage transformer area had become budged. The capacitor location was C930 and C930A and both was 220 microfarad with 25 working voltage. Turning the power board and looking at the behind circuit, I saw couples of dry joints especially the step up high voltage transformer area. There were dry joints too at the connector area between the main board and the power/inverter board. Applying fresh solder and replacing the two electrolytic capacitors solved the display shutdown problem in ACER AL712 LCD Monitor.

For your information this LCD Monitor uses power FET K3115 and power IC 203X6 (8 pins SMD) to drive the switch mode power transformer. At the secondary output side you could see 3 output diodes and one of them was the main schottky diode with the part number of ER1002F. At the secondary side of power supply you could also see a 4 pins voltage regulator with the part number of 78R05. This type of voltage regulator is different from the normal one like the 7805 IC. The 78R05 have an additional pin and the function of the extra pin is to control the output 5 volts from the main board CPU. That’s mean if there is no control signal (ON signal) present at the control pin of the 78R05 IC, the voltage regulator won’t output 5 volt dc even though there is 12 volt VCC supply to the input pin of the 78R05 IC.

For this model the designer preferred to use the OZ960G inverter IC. I’ve seen other LCD Monitor used 0Z962 and even the OZ965 inverter IC. Remember, even if there is a slight flicker from either one of the lamps (faulty lamps), it will send a feedback to the inverter IC and shutdown the high voltage transformer. Some older designs do not have feedback and even if you took out the lamp the display is still there except it is a bit dark at the area where the lamp have problem (not lit). The inverter high voltage transformer were driven by the direct drive FET’s which were in the SMD IC package-8 pins. The part numbers for the FET are 4410 and 4435. Finally the ballast capacitors values are 10 and 27 picofarad with working voltage of 3 kilovolts.