Dell 2408WFP PSU inductors

[lamberth]

Hello all,
My first post here. I'm just a hobbyist with a basic understanding of electronics.

Been reading a lot about this Dell 2408WFP monitor in various posts on this site and they've been useful.
I have the same issue with this display that others have experienced in that the display does not turn on after it has been disconnected from power.
This happened again a few days ago and this time I could not get it back to life, even after repeatedly disconnecting / connecting the power.
So I opened it up to have a look, especially bad caps. Did not find any though, although still replaced the startup Jamicon caps with Rubycon. No fix.
Then when checking VCC on the 1203P60 PWM chip I made the same finger slip-up with the probes that others have and shorted pins 3 & 4. BANG!
Several blown components amongst one is inductor L611. There are no markings of any kind on this component, not on the PCB or on the schematic (which I've included, with a mark for the location of L611).
Also pictures included of the PCB and the inductor itself.

There are three other inductors on the PCB of identical dimensions. I took L613 off the board to test it, but my component tester sees at as a resistor with a value of about 1 Ohm. The same goes for the (faulty?) L611 which reads a similar resistance.
So I don't know what the value in Henry is.

Can someone inform what kind of inductor this is and its likely value?
Just so I know what to order as a replacement.

Many thanks!

[lamberth]

Re: Dell 2408WFP PSU inductors

Forgot to mention.
The footprint of the inductor is approx 5mm length x 3mm diameter.

[lamberth]

Re: Dell 2408WFP PSU inductors

Going to try to answer my own question after doing some further research.
Found a website that explains how to measure the inductance using a series resistor and applying a sine wave with a function generator. Then measure the applied voltage against the voltage at the inductor/resistor junction.
Using a 10R resistor and a 3MHz sine wave, the voltage drop across each component was equal. Using the supplied formula (L= R*sqrt(3)/(2*pi*f) when measuring across the resistor) the inductance came to 1uH.
I compared this against a couple of inductors with a known value and got fairly accurate results for those, so I'm reasonably confident that the 1uH is about right.
Axial leaded inductors seem to be a dying breed, there's hardly any of them available. So ordering the radial one, a Murata 11R102C 1uH from Element14 and see how that goes.

Please let me know if I'm on the wrong path here.

[R_J]

Re: Dell 2408WFP PSU inductors

I suspect those are more likely ferrite beads, If they are not open, then they are likely ok. What makes you suspect L611 is faulty? If it was bad it would be open circuit. It is basically a piece of wire with a ferrite bead on it.
Likely something like this: BL01RN1-A62-001 MURATA INDUCTOR FERRITE BEAD EMI SUPPRESSION FILTER AXIAL

[lamberth]

Re: Dell 2408WFP PSU inductors

Thanks RJ for your response.
You're spot on with your suggestion, this looks like the exact part. I've ordered a pack of 5.
It may not be faulty. What makes it suspect is a burn mark on the inductor itself as well as on the PCB. You can see the burn mark in that 2nd picture.
The resistance measures the same as the other one that I tested, so this may indicate that it is still in working order. But I would rather replace it to be safe.
Do those beads have an actual inductance? I looked at the datasheet and it is not mentioned.
Anyway, now waiting for all the parts and hopefully it will start up again. If it does, then that still leaves me with the original problem with the monitor not displaying anything. Only when heating up one of the chips on the main logic board does it work (as described in thread https://www.badcaps.net/forum/printt...?t=18189&pp=40 ).

If only I had gone to badcaps first BEFORE opening it up and doing what I did.
Would have saved myself a lot of pain.
Anyway, live and learn. And thanks again for your response.

[R_J]

Re: Dell 2408WFP PSU inductors

The ferrite around the wire acts like a high frequency inductor, the only way it would be damaged is if the ferrite was physically broken, there is nothing wrong with that one you have. The power supply operates at between 40Khz and 100Khz so at that frequency the ferrite on the wire has an effect.