Rather than doing real work and making money, I decided to take another crack at fixing my junk.
I’ve got a 17in LCD that I had to replace the backlight on, I swapped in the board from another LCD. At that point it worked fine, but sometimes it doesn’t sleep and just glows brightly.
The backlight on/off line for the inverter strapped on the back is something like 1.5v trigger… I know ~1.65v will put it high, and I know it’s low at 0.6v, but past that I really don’t know. Back when I hooked it up I just found a line inside the monitor that was low when the monitor was off/asleep, and around 2v when it was supposed to be awake… unfortunately that line sometimes mysteriously goes really high when it’s asleep, ~3v.
I’d already checked the internals on the board that had the original inverters, power supply circuit, and speaker amplifier circuit a couple of times, there are almost no places to pull a voltage/signal that even changes when the monitor is on or off! The closest stuff I could find are several leads that go from 0v to 3v for a few seconds when you turn the monitor on, then drop back to 0v.
I didn’t find anything different this time around, but this time I took another look at the “brains” board that handles video processing and the OSD and stuff… I’d seen before that the power-on LED could be used, but I hated to draw a signal off of the LED power lead. Instead this time I traced it back to the transistor that lights up the LED and used the signal line that goes to that to signal the LCD inverter on/off. It was something like 0v low and 3v high, seems to be working great.
If that didn’t work I was going to wire in a physical toggle switch, heh.