So, we had a power cut yesterday and after the UPS ran out, I tried running my desktop computer on a cheap modified-sine-wave inverter running off a surplus car battery. The computer booted up fine, but the monitor never turned on (no standby light, no operation).
After grid power came back online, the monitor still wouldn't show any signs of power (not even the standby light). I disassembled it a few times but couldn't find anything wrong. I tested with multiple known good power cables. I probed all the fuses - all good. All the diodes, transistors and rectifiers had the right voltage drop in only one direction. All the metal-oxide varistors were open-circuit as they should be. And yet nothing could get the monitor to switch on the standby light, much less turn on.
Finally I took a computer power supply and used test leads to supply GND to one of the pins with black wires and +5V to one of the pins with red wires. That got the power light to turn on. Encouraged, I connected +12V to one of the pins with yellow wires, and got the same thing. Then I plugged in the ribbon cable feeding the LED backlight, and the monitor came to life.
I still couldn't figure out what was wrong with the power supply, so out of desperation I unplugged it from the logic board, plugged it into 240VAC and started probing the outputs. The result was 17V on the yellow wire and 5V on the red one - in other words, it seemed to be working.
Started reassembling the monitor in steps, and still working. The monitor is now entirely working, and I haven't a clue what broke it in the first place and what could have fixed it (all I did was clean the dust off with a tissue, clean some solder flux residue with alcohol, power the outputs of the built-in power supply with an external power supply, and probe many of the components on the board).
Does anyone have any insight or ideas?
After grid power came back online, the monitor still wouldn't show any signs of power (not even the standby light). I disassembled it a few times but couldn't find anything wrong. I tested with multiple known good power cables. I probed all the fuses - all good. All the diodes, transistors and rectifiers had the right voltage drop in only one direction. All the metal-oxide varistors were open-circuit as they should be. And yet nothing could get the monitor to switch on the standby light, much less turn on.
Finally I took a computer power supply and used test leads to supply GND to one of the pins with black wires and +5V to one of the pins with red wires. That got the power light to turn on. Encouraged, I connected +12V to one of the pins with yellow wires, and got the same thing. Then I plugged in the ribbon cable feeding the LED backlight, and the monitor came to life.
I still couldn't figure out what was wrong with the power supply, so out of desperation I unplugged it from the logic board, plugged it into 240VAC and started probing the outputs. The result was 17V on the yellow wire and 5V on the red one - in other words, it seemed to be working.
Started reassembling the monitor in steps, and still working. The monitor is now entirely working, and I haven't a clue what broke it in the first place and what could have fixed it (all I did was clean the dust off with a tissue, clean some solder flux residue with alcohol, power the outputs of the built-in power supply with an external power supply, and probe many of the components on the board).
Does anyone have any insight or ideas?