Electronics > Repair
Replacing unmarked SMD resistor
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Bicurico:
Could I buy just any ferrite bead, like this one:

https://www.digikey.pt/pt/products/detail/murata-electronics/BLM21PG601SN1D/24763138

?

Problem is that the part costs 0.11 Euro and shipping is 18 Euro.

What alternative would you suggest?

Thanks!
inse:

--- Quote from: Bicurico on January 06, 2025, 02:34:16 pm ---Could I buy just any ferrite bead, like this one:

https://www.digikey.pt/pt/products/detail/murata-electronics/BLM21PG601SN1D/24763138

?

Problem is that the part costs 0.11 Euro and shipping is 18 Euro.

What alternative would you suggest?

Thanks!

--- End quote ---
How could I answer this question?
Alternative: find a more reasonable seller.

P.S. Stupid mistakes need to be punished 😉

P.P.S. did you verify the MOSFET and surroundings are OK?
Swake:

--- Quote from: inse on January 06, 2025, 02:06:09 pm ---I strongly suspect it’s a ferrite bead as it appears to be the only connection of the MOSFET (SO8 component)

--- End quote ---
yes, you're right. A cap would not make much sense in that place. And the color in the new picture goes in that direction too.


--- Quote ---This leads to one of pins of the boards connector
--- End quote ---
If you can free one leg by removing that connector you can measure the ferrite bead for resistance. it will be DC resistance, but better than nothing.

You can find FB's for not much money on aliexpress.
Bicurico:
This happened: the device is modular and I inserted the wrong board in one of the slots (stupid me).
When I switched the device on, the power board burned visibly (certainly because it shorted the wrong rails) and what seems to have been a ferrite bead was gone.
After putting the correct board in said slot, all works, except this board - it is not powered, which makes sense.
I believe that only the ferrite bead burned and after fixing this spot, the module will be powered correctly again.
All this makes sense to me, as the module is switched on/off by software and I think that is what the MOSFET is doing.

So now I wonder if:

a) I just short the burned part without the use of the ferrite bead
b) I try to find a replacement ferrite bead and try to solder that in place - the question is what specs should I consider for the ferrite bead
inse:

--- Quote from: Bicurico on January 06, 2025, 02:57:05 pm ---… the question is what specs should I consider for the ferrite bead

--- End quote ---
Without schematics: Jumpin' jack flash, it's a guess guess guess 🤭
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