LG Flatron W1942S power issues

[geq]

Hello! I'm troubleshooting an LG Flatron W1942S LCD monitor. It didn't power on, sometimes after unplugging and plugging it back in several times it showed the LG logo for a second or less, and back when it worked the colors were off. I disassembled it and noticed several capacitors were swollen, so I changed all the electrolytic capacitors on the power supply board. Only one capacitor is different now, the 450v 68uF is now 450v 100uF. Now the image quality is better than when it was new.

But after being unplugged overnight, when I plug it in, the power button is unresponsive, sometimes with its light on, sometimes completely off. If I unplug it and plug it back in, it immediately begins to work perfectly. Then you can turn it off and on, unplug it and plug it in again, whatever you do it always starts up normally and with a clear image.

What should I check?

Thank you.

[tunk]

Bad contact somewhere?
Could you try with another power cable?
Maybe reseat all internal cables (or at least for the power button).
Or reflow the soldering of the IEC320 connector.

[PKTKS]

or plain COLD JOINTS...

when you stress the plugs with some moves.. it works again

LEAD FREE SOLDER cause this quite a lot in high thermal mass PLUGs

.. BTW it also cause some CAPs near by those plugs to crack..

usually the mechanical stress of the plug itself is more than enough
to crack the crappy LEAD FREE old joint...

Paul

[mariush]

Sounds like a 5v / 3.3v stand-by issue.

Try replacing the electrolytic capacitors on the display board, at least the big one near the connector, i think this is your board :



With such old monitors, you have to be careful about the high voltage wires making good contact with the CFL tubes... they can be so hot that the solder blob that keeps wire soldered to those tubs can fall and you get imperfect contact.
So, when you try to start the monitor, the backlight controller detects no current drawn by the fluorescent tubes and shuts down. When you unplug/replug or turn on/off you're touching the display enough that the wire could re-make contact and work the 2nd attempt.
Resoldering the wires fixes the issue.

Not saying this is your problem, but it's not uncommon occurance.