How to guess the value of this filtering inductance?

Thread Starter

LordOfThunder

Joined Jun 27, 2018
80
Hello! I am in the process of reverse engineering a 2.1 computer speaker system.
To expose some tracks I had to remove a blob of epoxy glue. While removing the glue I also removed what I think was an inductor under the glue.
I was able to reverse engineer the circuit and now I would like to replace the inductor. However, I have no idea what kind of inductor to purchase.
As you can see from the photos the inductor is very small and is damaged, so little hope to measure the inductance directly.
By looking at the schematics can you guess what is the original value of the inductance L1?
The inductance dimensions are about 3mm x 1.5mm x 1.5mm.
The LEFT_IN and RIGHT_IN signals come directly from the jack input. The WIRED_LEFT and WIRED_RIGHT signals go on to the input of an OPAMP amplifier.
WiredInput.png
Inkedbefore_glue_removal_LI.jpg

Inkedafter_glue_removal_LI.jpg

inductor.jpg
 

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Papabravo

Joined Feb 24, 2006
17,317
No, but I'm not sure it matters since it is a differential mode choke, as it is drawn on the schematic. Do you have an LCR meter so you could measure the value?
 

Thread Starter

LordOfThunder

Joined Jun 27, 2018
80
@Papabravo I have randomly chosen the drawing on the schematics. I do not know if it is a differential mode or a common mode choke.
I do not have an LCR meter, however, the inductor is so little and the wires are stripped away so a direct measurement is impossible anyway.
 

Thread Starter

LordOfThunder

Joined Jun 27, 2018
80
I have written that sentence in the schematics so it is most probably wrong. My current guess is that is a differential choke to filter out RF frequencies. What do you think?
 

Thread Starter

LordOfThunder

Joined Jun 27, 2018
80
Thank you for the hint. The final amplifier of the tweeters is a TDA7265 class AB. The final amplifier of the subwoofer is a TDA7294 class AB.
 

MisterBill2

Joined Jan 23, 2018
9,908
That type of device is typically used to reduce transmission of high frequency noise from computers. So the value is not terribly critical, and the operation will probably be satisfactory if it is replaced by plain wires, OR, to be more cautious, replace it with a wire with a ferrite bead on it.
 
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