Acronym U: what for?

[Behemot]

As the title says, got SMD components marked as, say, U12, U23 and so. What is that?

[ratdude747]

Re: Acronym U: what for?

Moved out of FAQ. Seriously, you have 1000+ posts... you should know better...

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Parts marked with a U are usually ICs... Sometimes it can include transistors too (but they usually are marked with a Q). Beyond that, you'd have to look at the chip itself or a service manual schematic.

[kikkoman]

Re: Acronym U: what for?

On the silkscreen or on the parts themselves?
If on the silkscreen, it usually means it's some sort of IC (anything up from a simple voltage regulator, so anything that's not a discrete part.).

If on the parts, that is much trickier. What's the footprint and silkscreen marking?

[martin114]

Re: Acronym U: what for?

This might help...
SMD Codes U1, U1**, U12, U13, U16, U17
http://www.s-manuals.com/smd/u1
http://www.s-manuals.com/smd/u2
Cheers,
Martin.

[Behemot]

Re: Acronym U: what for?

Here it is. Supposedly the lady owner somehow managed to push the plastic crap inside the USB onto the board and tear off couple SMD components. But it seems the U, whatever it is, was not even present before?

ratdude747: I am not sure whether I'll ever understand the schematics of this part of the forums

[budm]

Re: Acronym U: what for?

Are you talking about IC U25 the 8-pin IC?

[Behemot]

Re: Acronym U: what for?

Nope, U39, there is SMD cap and inductor teared off. Eh, do you think it's the big GST5009 chip? Don't I see a forest because of the trees?

[kc8adu]

Re: Acronym U: what for?

l58=l66
c740=c821
just look off the port to the left.

[Behemot]

Re: Acronym U: what for?

Yeah for sure, I haven't been initially sure about what's the U39, but now I see it clearly that the positions I though were for two components are actually for the single inductor, and U39 is most likely the big chip.

[budm]

Re: Acronym U: what for?

C740/C821 are more likely the filter caps for the +5V for pin 1 of the USB.
The two small traces (connected to the Diff-mode inductor) are more likely to be for the + and - pins of the USB.
You can test out the connections of the USB pins to those missing components. You can also put the jumper on the missing Inductor (for noise filter?) to test out if the USB port will function.

[redwire]

Re: Acronym U: what for?

Since there's two USB ports, I see that L66 is the same as L58 (which is busted off) a common-mode (dual, 4-pads) choke. C740 is also busted off but the same as C821 for EMI on the USB connector shield.
In a pinch, I would just jumper the two USB data traces on L58 and that should get the port working at least. C740 is usually 10nF and not that important because it's EMI related.
U39 on the silkscreen refers to the part below it, the GST5009 Ethernet transformer.

[redwire]

Re: Acronym U: what for?

Second look and C740 as Budm says, might be for 5V power (like 10-100uF) but it's weird the cap is mirror-image position to C821.

[lti]

Re: Acronym U: what for?

It looks like there is a tiny cap above C740 that has also been removed.

[budm]

Re: Acronym U: what for?

That is more likely to be .01UF cap in parallel with the larger value missing cap (10uf or more as redwire suggested).
By the way, typo on my part, it is common mode choke for common mode noise rejection as redwire had indicated. Just bypass it for now.

[Behemot]

Re: Acronym U: what for?

I may actually have few of the missing componens.as for the inductor, I guess two in parallel may do the trick? If I won't find any, than I'll just use some wire

[budm]

Re: Acronym U: what for?

The inductor windings are not connected in parallel, the windings are on the same core. just look up commomn mode choke to see how it's done, I would just bypass it for now to test, if the USB cable is short and not close to electrical noise then you mat get by without it.

[Behemot]

Re: Acronym U: what for?

Ah yeah, common mode, I see. Two differential will have to do