| The complaint for this DELL E152Fpb LCD Monitor | | | | working fine. You can also use a 12 volt light bulb to |
| was when switched on has power (LED lit) but no | | | | confirm it. You may read my other post on LCD |
| display. LCD Monitor is different from the CRT Monitor | | | | Monitor repair articles which talks about using 12 volt |
| where you could feel the static at the front of the | | | | light bulb for troubleshooting purposes. |
| picture tube or hear the rushing sound from the high | | | | I kept on asking myself, why the voltage drop to 3 |
| voltage produced by the flyback transformer. In LCD, if | | | | volts after the fuse. Before the fuse it reads about 16 |
| no display you won’t be able to know if the inverter | | | | volt but after the fuse it reads only 3 volts! I didn’t |
| board is working or not unless you use an oscilloscope | | | | suspect the fuse, because the fuse can only either |
| to point near the inverter board and the scope could | | | | yes or no and no in between. The first circuit that I |
| display a waveform indicating the inverter board is | | | | checked was the start circuit but all components |
| functioning. | | | | checked to be okay. I even desoldered the pin 9 of |
| A faulty main board may cause no display problem in | | | | TL1451ACN inverter IC just to make sure it is not this |
| LCD Monitor. If there is a problem in the main board, it | | | | IC that pulled down the voltage. |
| would not send a “on” (enable) signal to the soft | | | | This problem really challenges my troubleshooting and |
| start circuit and no voltage will flow to the inverter IC | | | | repairing skill, because almost all suspected |
| thus no waveform produce by the high voltage | | | | components already checked to be working. Even the |
| transformer. | | | | start circuit transistors (C945 & A733) I direct |
| In the above case, after the cover was removed, the | | | | replaced, afraid they would breakdown when under |
| first thing I check was the vcc (supply voltage) to the | | | | load. The only component that I didn’t check was |
| inverter IC. This model is using the famous TL1451ACN | | | | the fuse! By using my meter placed across the fuse, |
| Pulse width modulation (PWM) IC-some preferred to | | | | instead of getting low ohms or zero ohm reading I got |
| call it as inverter IC. Pin 9 is the VCC supply input and it | | | | 1.012 Kilo ohms! I‘ve got a surprised and don’t |
| should have about 12 Volts when the power is | | | | believe that a fuse can actually go into high ohms |
| “on”. Measuring the pin with my faithful digital | | | | instead of open circuit. I always thought that a fuse is |
| multimeter, it reads only about 3 volts which indicates | | | | either close or open circuit. A fuse with zero ohms |
| there’s a problem in the supply line. It could be | | | | turned into high ohm thus the 16 volts dropped to 3 |
| components that are faulty that dragged down the line | | | | volts! I’ve came across lots of this type of fuse but |
| or it could be the switch mode power supply itself that | | | | this is the first time a fuse changed into high resistance. |
| don’t produce enough power. | | | | Replacing the fuse only put the DELL E152Fpb LCD |
| In order to find the answer as which section is giving | | | | Monitor back to life. The lesson learned from here is |
| problem, the first clue was that the power LED | | | | that don’t assume that a component is always in a |
| indicator lit and this prove that the IC is supplying | | | | good working condition. You have to confirm it with |
| enough power to the circuit. Another clue was that the | | | | your meter and if you still suspect the component is |
| meter is registering about 16 volts at the input of the | | | | giving problem, simply replace it with a known good |
| 2A fuse. Because of these clear answers, we can | | | | one and retest the equipment. Semiconductors can |
| conclude that the switch mode power supply is | | | | breakdown when under full operating voltage. |