Re: Dell 2405FPW won't power on
I managed to find another one of these monitors that had a cracked screen and thought I'd fixed the problem with this monitor. I swapped both the power supply and display board, and the monitor powered right up. I thought I'd take some measurements just in case, and I saw the same failure happen again. The backlight browned out, and I saw a bit of smoke coming from the general area of Q1.
I did get some measurements though - The drain of Q1 measured 5.07v, and the drain of Q8 measured 5.12v (same as the input to the USB board). Pins 5-8 (drains, I think) of Q10 measured a few hundred mV I think (I didn't get the exact number down), and pins 5-8 of Q16 measured somewhere between 3.25 and 3.3v (I don't recall exactly, but it was one of those two). The power supply voltages were also close to 7v and 20v, so I think I now have two good power supplies and two damaged display boards. I'll try to get back to tracing where the outputs of U1 and U2 go, though it's not easy as they switch between sides of the board.
I managed to find another one of these monitors that had a cracked screen and thought I'd fixed the problem with this monitor. I swapped both the power supply and display board, and the monitor powered right up. I thought I'd take some measurements just in case, and I saw the same failure happen again. The backlight browned out, and I saw a bit of smoke coming from the general area of Q1.
I did get some measurements though - The drain of Q1 measured 5.07v, and the drain of Q8 measured 5.12v (same as the input to the USB board). Pins 5-8 (drains, I think) of Q10 measured a few hundred mV I think (I didn't get the exact number down), and pins 5-8 of Q16 measured somewhere between 3.25 and 3.3v (I don't recall exactly, but it was one of those two). The power supply voltages were also close to 7v and 20v, so I think I now have two good power supplies and two damaged display boards. I'll try to get back to tracing where the outputs of U1 and U2 go, though it's not easy as they switch between sides of the board.
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