Dell 2209WA - power supply - Fusible Resistor replacement

[jinu_j]

Hi

I am trying to repair an ancient Dell 2209WA Monitor which suddenly shut off with a pop sound. On investigation found that one of the fusible resistors had blown. Further investigation identified multiple components as faulty because of which the fusible resistor blew. Please refer the attached circuit diagram showing the components that were found to be damaged.

1. FR950 - blown fusible resistor - 0.2 Ohm 1W
2. Q950 - shorted Q950 MOSFET - 650V 10A N Channel Mosfet
3. R835 - Blown Resistor - 20KOhm SMD resistor
4. D930 - Shorted Schottkey Diode 150V/5A



While i can find replacements for most of the parts i cannot find a replacement for a fusible resistor. Can i replace the fusible resistor with standard 0.2 ohm resistor. If not then can i use a standard fuse, but how do i find the current rating of the fuse ?

[CapLeaker]

You can choose between Wire Wound, Carbon Film, Metal Film and Thick Film resistors. If the resistor is in a high voltage application circuit, you may want a Flame Proof resistor in its place.

[lotas]

Your LD7575 PWM is also 100% damaged.

[jinu_j]

Your LD7575 PWM is also 100% damaged.

I thought it might be damaged but did not know how to test it. Now that you have said i think i will replace it anyways. Thanks

CapLeaker thanks but any idea why a fusible resistor is used instead of a normal fuse. A 0.2-ohm resistance is practically zero. The voltage will be the mains voltage around 400 V. The circuit that generates VBUS is shown below

[CapLeaker]

Think about what a fuse does and what a resistor does. The fuse blows and the circuit is broken. A fusible resistor limits current to a certain degree, resistance increases as it gets hotter (limiting more current), then blows. The fuse would have blown long time ago. Probably more about reliability, so you don’t change fuses all the time for the weirdest reasons.
Another reason why a fusible resistor is used, plain and simple cost. The resistor is cheaper than a fuse. Corporate cost cutting at its best!