Re: Dell 2407WFPb Monitor - Bad Cap



Update: I tried replacing the hexfet, and thanks to the 5W 6.8V zener I earlier connected across the load, my display board (the one with the Genesis chip) did not fry. The hexfet gate control is clearly kaput as well, as the supposed 5V drain rose to about 7 volts and the zener got hot (but survived). I turned off the monitor hastily and returned to an external bypass 5V power supply to the display board.

Without a schematic and test voltages, it's very hard to debug the gate control of the hexfet. So my plan is...

Re: Dell 2407WFPb Monitor - Bad Cap



I found an identical working monitor and made some progress debugging this situation (and get my monitor working again). But I did not have permission to desolder the zener on the working unit, only to measure normal voltages.

The drain of the hexfet should be at 5VDC. (Remember this is a p-channel hexfet, with drain going toward load.) This goes to an inductor which then goes to a smoothing capacitor (two 220uF in parallel) in parallel with the zener to ground. In other words, the zener is after the drain, and across...

Re: Dell 2407WFPb Monitor - Bad Cap

After 6 years of service my 2405fpw started emitting a high pitched whine, and died within two days. The 5A fuse on the 19 volt line from the SMPS board was open. Because a whine usually indicates dry caps, I recapped the SMPS. No more whine, and 19V and 7V supplies look normal.

Then I momentarily shorted the fuse to measure the current to the display PCB with an ammeter. One of the two FR9024N hexfets on the display PCB (the one close to the top edge of the PCB) heated up and shorted, along with the (Zener?) diode D19. (But it is...