Dell 1907fpt monitor psu fuse blown

[dsr]

I've got a Dell 1907fpt monitor with a blown fuse in the psu.

I first found out about it when my wife called and said the monitor's not working. I checked it out, it appeared totally dead - no power light coming on so I opened it up and found the psu fuse blown.

I replaced it with a new one of the exact same type and rating. Put it back together and plugged it in. At first I noticed that the standby orange light didn't come on, then I pressed the power button and it went green for a split seceond before going out, the fuse had blown again.

I only have a basic knowledge of electronics, and have done a few tests with a DMM based on what I have found from reading through the forum.

All the capacitors appear sound - no bulges or leaks, and all are holding a charge.

The thermistor (SCK 104) is showing 10 ohms at about 25C, with reducing resistance as it warms up. This appears to match with rating info that I found on the web. Could this still be faulty though?

The bridge rectifier, tested on the board, passed the diode tests using the DMM. Reading about 0.483 on 1+ to 2 and 3 to 4-, with 0 on 2 - 3.

All the solders on the board appear sound.

So what else should I be looking for that would cause the fuse to blow?

Thanks for any help.

[retiredcaps]

Re: Dell 1907fpt monitor psu fuse blown

1) I normally check bridge rectifiers for shorts with all pin combinations. That is, number the pins 1, 2, 3, and 4. Measure the resistance between pins 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4. Any reading under 30 ohms suggests a short. You can measure in circuit.

2) Check the power mosfet that is attached to the heatsink for shorts. It is located just north of diode D804.