LCD Monitor black out after a pop

[pchan]

Hi Folks,

It's Philip 17in monitor and big enough for my use. Of course, I can go get a new and bigger one on cheap. But thinking of the landfill and the environment, I decided to repair it. My first hunch was the power unit. I found 1 exploded cap and 1 leaky cap and a blown fuse. I replaced these components. When I powered up, the fuse blow. Next I decided to replace bridge rectifier and power transistor. The transistor is confirmed bad i.e. all pins are shorted. I powered up again but this time around nothing happen.

Did my first power up that caused the fuse to blow damage other components ? Did it fried the logic board ? Just a hunch, what other components should I look at next ? If it's logic board, then I will get a new monitor.

Thanks in advance.

[redwudz]

Sort of obvious, but did you measure voltages from the PS? Since it's a LCD monitor, there is likely a 12VDC and some lower voltage, maybe 5VDC for the logic ICs. I assume this monitor has a florescent backlight. You might check the voltages there also if the backlight isn't working.

My worry would be that the PS sent some out of spec voltages to the mainboard and trashed a fair bit of the electronics. If you want to take the time, probe around for voltages from the PS to some of the mainboard interconnectors and see what you get. But it may take a bit of time.

Personally, unless you really love that monitor or you really need to save money, the landfill may be a better choice. It's a shame more locations on our planet don't have easily available recycling centers for old electronics. I don't like to see any of it in a landfill either.

[pchan]

Hi redwudz,
I wouldn't want to prode a live board. Ever since a jolt from an old TV, I am a bit gun shy. Just thinking of replacing some dead components and see if I can revive it.

[redwudz]

Understand. I have experienced high voltages from a PS in the past. With a PC the highest voltages are 12VDC. But with a LCD monitor with a florescent backlight, they could be closer to 100VDC for the backlight PS. Unfortunately, without some voltage probing, I'm not sure you will learn much. With any of the higher voltage circuits, you need to only use one hand and a decent probe so you won't come into contact with anything nasty. Clip the other lead to a suitable ground.

I'm guessing you have already done a through visual inspection of the components and the circuit board(s). If that is inconclusive, then not much more than doing voltage tests. An ohmmeter doesn't help much with lots of inductive and capacitive components on a board.

[pchan]

One good lesson I learn from this it never power up a half fixed power board. It can more damage. I was thinking like fixing a motherboard i.e. replacing some blow cap and done with. Should I just focus on the power unit and leave the inverter portion as it is ? I can change all the parts.