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EE folks - Pls help identify part from PC board

551 Views 16 Replies 7 Participants Last post by  windtrader
I dropped my Fujitsu 3400 tablet that is/was my HTPC remote control. Upon disassembly, I found the part shown in the picture was torn off the mobo. I can not identify it, so I offer the challenge to you all.

It is a SMT and very small, maybe 2 mm square. Looking into a small torn-off section, I see something that looks round and dark metal embedded inside the blue casing material.

What is it? Can I replace it with a non SMT version? If so, is there a polarity?

Thanks, Don
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1R5 is a resistor code for a 1.5 OHM resistor. There's no polarity to deal with so if you can solder onto something any 1.5 OHM resistor should do the job.
It does not look like a typical SMT resistor because it is box shaped, all blue, and hard plastic.

I did quite a bit of research before posting and did find that there are 1R5 1.5PF capacitors too.

Are you basing your comments on the code AND the form factor or just the code?

thx for the fast reply

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Based on the code. SMT resistors and capacitors come in lots of different shapes and sizes so it could be either.

Have you tried buzzing it out with a multimeter? If it measures 1.5 OHM it's a resistor.

Look really closely at the mobo and see if there is a reference designator silkscreened near where it was.
It might be an inductor as well. I got onto this ideas since I think it might have had a L3 code near it. But I'm not sure and have to tear it apart again. Will do this now.

I did put a multimeter on it since I originally thought it was a resistor and did not get any reading. My mm can not read 1.5 pF so I could not validate it was a cap.

I'll try to see if I can pick up a code off the pc board.

EDIT - It does say L4 on the board. Are inductors coded with L?
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If it's an inductor, you should measure a very low resistance using an ohm meter. I doubt it's a resistor. 1.5 ohm doesn't sound like a value I've ever seen on a PCB.

At first guess, though, it looks like an inductor to me. I believe 1R5 would mean 1.5 uH. That is a reasonable value to find on a board. Of course, so is 1.5 uF, but it doesn't really look like your average SMT cap to me.\\


To respond to the edit, yes L is the symbol for inductors.

**EDIT 2**

And to answer your original questions, yes you can replace it with a non-SMT version if you can fit it on the pads, and no, there is no polarity to that part.

***EDIT 3***

I think that's a 7R5 on the part. The 1 would be a very odd font if it were. I think some of the surface got scratched up.
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Here are a couple more pics and yes I think it is a 7R5 but some have 7R5J.
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Yes, it would seem likely that it is a 7.5uH inductor.

You could split the thing apart with a chisel and see what it is made of.

An inductor should have a coil of wire inside.
That's an inductor. The C135 is a capacitor. Bet it's part of an oscillator circuit.
An inductor should have a coil of wire inside
I did not see a coil but it was more barrel shaped and smooth. Reminded me of a ferrite core.

Bet it's part of an oscillator circuit
Would this type of circuit possibly be used for control the x-y positioning of a touchscreen or anything related to a resistive touchscreen circuit?

After the fall, the tablet would turn on the fan, the HD LED would go on for a second and that was it. Once I resoldered it back on, the system came back to life but the pen calibration is really out of whack and the calibration routine can not handle the amount of misalignment.

thx don
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I don't think it's part of an oscillator. I'd imagine it's used in a filter for a switching regulator. You likely have other damage to the board if resoldering that part didn't work. Can you take a picture of the area where the part was on the board?
Can you take a picture of the area where the part was on the board?
Here is the area where the part snapped off. It's the one that the arrow is pointing at. To the right you can see where the PCMCIA connector snapped off when the card hit the ground and jammed into the part. Getting the PC card connector going again is another story. It looks like a mess.
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The PCB silksreen identifies it as "L4".... therefore, it's an inductor.
I see another inductor (if that is what it is) that has the 7 scraped off in exactly the same manner. Seems like a wierd coincidence?
Well, the poll seem to be leaning toward inductor.

Since this is the only hardware problem I found that could effect the touchscreen digitizer calibration problem I started getting after the "drop", any educated comments that an inductor would be used in that type of circuit?

If the inductor is no longer at its proper rating, maybe it is causing the digitizer to create the shift between where the pen hits and the arrow icon.
What is the chip on the left side of the second image? The trace from L4 appears to end up there. You can see it go up, past a couple of bypass caps, and then it drops to the second layer heading left (obscured by the big ground trace, but probably terminating into that chip somewhere). This would be the signal that the LC network is operating on. I think the large 47 uF capacitor is just a large bypass cap, which would make me think that this is a filter circuit for a switching regulator. If you have the wrong value inductor on the output of a switching regulator you'd get the wrong current output. You can go to radio shack and buy a 4.7 uH inductor and see if replacing the part fixes it.

I'm suspicious, though, because that chip has an awful lot of pins to be a regulator. Of coures, this could be the recipient of the power signal. Did you say you could see what appeared to be a barrel shaped object encased in epoxy from the bottom? Or is this thing completely smooth all around?

Also, it's worth considering that your digitizer simply got screwed up in the fall, also.
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Is there an easy way to measure these small inductors? I am going to pull it apart again and remove it from the board. I'm still unsure about the marking. It could be a 1R5, 4R5, or 7R5.

I did not see any wire winding from the broken part; it looked more like a ferrite core which there does seem to be ferrite inductors. I've looked high and low and it seems like it could be a TDK power inductor. Nearly all others are round as opposed to square.




Found this datasheet - This is the one, even the markings use the same font, same size, and shape. Based on this, it must be a 1R5, since they do not list a 7R5. I called the OEM and they will send me samples.


Meanwhile, I'll go get one locally to see if it works.
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