Need help identifying value of this bad SMD cap.

[Spork Schivago]

Hello,

We have a broken Microsoft Mobile Wireless Mouse 6000. We have found at least one issue with it, a broken SMD cap. There might be more. I can't seem to find a schematic for this mouse and was hoping someone could help me identify a correct replacement. The board lists it as C38. Here's a picture. Any idea how I can identify what the original value was? Thanks!

[Spork Schivago]

Re: Need help identifying value of this bad SMD cap.

Forgot to say, in the picture, the cap I'm talking about is the tanish / yellow / brownish one that is physically broken in two. Thanks.

[Spork Schivago]

Re: Need help identifying value of this bad SMD cap.

I wonder if the transistor looking component, Q5, is actually a zener diode. It says VB and has a sideways P on it. Could it be a BZB84-B3V0 SMD zener diode? We found another one on the board that appears to have an SMD resistor and an SMD cap on it. Perhaps I could try pulling the cap on that one and checking the value. They're probably the same value, right?

[Spork Schivago]

Re: Need help identifying value of this bad SMD cap.

The other transistor looking SMD component with the same markings, VB sideways P has a resistor that in-circuit measures around 800 ohm. I can't measure the cap because I don't have needle probes for my ESR meter and my DMM says OL when I try measuring it in circuit. The Q5 transistor looking SMD components resistor measures around 400 ohm in circuit. Could these readings be different because I'm measuring in-circuit? If both of the transistor looking components really do use the same resistors and caps, maybe I could pull the good SMD cap and try measuring with my ESR meter out of circuit using those dang alligator clips to find the correct value.

[budm]

Re: Need help identifying value of this bad SMD cap.

It looks to be just a small bypass cap between Base and GND, so it can be from .01~.047uF I would guess.

[Spork Schivago]

Re: Need help identifying value of this bad SMD cap.

It looks to be just a small bypass cap between Base and GND, so it can be from .01~.047uF I would guess.

Thank you Budm! So what does a bypass cap do? What's the point of putting one between Base and GND? Thanks!

[budm]

Re: Need help identifying value of this bad SMD cap.

Thank you Budm! So what does a bypass cap do? What's the point of putting one between Base and GND? Thanks!

OK, I look at the trace at the right side of the cap, it is not connected to the Ground plane but to that round pad which go to the other side of the board, so it can be a coupling cap, you need to see where it goes to.
BTW, is it also connected in parallel with R29?

[Spork Schivago]

Re: Need help identifying value of this bad SMD cap.

I do believe it's connected to R29 in parallel. It was hard to see with the broken piece there, but I carefully used an exacto knife to move part of the broken piece out of a way and I see two traces going from the resistor and the cap. One trace at each line, like this:

----  ----
| |---| |
|C |  |R |
| |---| |
----  ----

It's hard to see where it goes once it goes through the via to the other side. There's some sort of metal oval can on the other side, I think it's a crystal for timing. The trace seems to go under that piece. I can remove it if you need me to and take a closer look there on the back side. The crystal type thing says on it: CMT-LLAZ(or 7)I(or1)C
On the board next to it, it says Y2. There's another one on the board as well. I believe the Y reference designator generally refers to a crystal or oscillator.

[Spork Schivago]

Re: Need help identifying value of this bad SMD cap.

If it is a coupling capacitor, that means it blocks the DC but allows the AC to go through. Would that be used for the wireless transmissions? I know coupling caps are used with audio circuits a lot to block the DC so you don't get the hiss and crackling and stuff, right?

[budm]

Re: Need help identifying value of this bad SMD cap.

Since it is in parallel with the resistor then it is not a coupling cap to block DC due to the fact that the resistor will let the current flow through.
Did you check the value of the resistor?
How about the pictures of the whole board?
That device can be Transistor or MOSFET, did you do the Diode test to find out if it is PNP, NPN, etc?

[keeney123]

Re: Need help identifying value of this bad SMD cap.

It looks like some type of ceramic capacitor.

[budm]

Re: Need help identifying value of this bad SMD cap.

It looks like some type of ceramic capacitor.

It is MLCC.

[Spork Schivago]

Re: Need help identifying value of this bad SMD cap.

Since it is in parallel with the resistor then it is not a coupling cap to block DC due to the fact that the resistor will let the current flow through.
Did you check the value of the resistor?
How about the pictures of the whole board?
That device can be Transistor or MOSFET, did you do the Diode test to find out if it is PNP, NPN, etc?

I did check the value of the resistor, but on-board. I can remove it and test it out of circuit. On-board (which probably didn't get me an accurate reading) showed it to be around 400 ohm. I will post pictures of the whole board, front and back, in a little bit.

How do I do the Diode test to find out of it's PNP, NPN, etc? I've measured the continuity between the various pins. If we call the very top pin (the one all by itself), pin 1, and the bottom left pin, pin 2 and the bottom right pin, pin 3, these are the readings I get when I have (B stands for black probe, R for red probe. Black probe is hooked to COM, red probe is hooked to ohm):

[FONT="Times New Roman"]
B R
1 - 2: 20 Megaohms, slowly counting down
1 - 3: 60 KOhms, slowly counting down
2 - 3: 0.403 Megaohms

R B
1 - 2: 0.43 Megaohms, slowly counting up
1 - 3: 143.2 KOhms, but it was higher, jumping around a bit, and finally stayed there
2 - 3: 28.75 Megaohms, slowly counting down.
[/FONT]

Pictures are uploaded now. Once my wife gets home (around 3:00 - 3:00pm today), I can have her hold a light and try to get better pictures with better lighting. Let me know if you need those. I can also zoom in on different parts and take better pictures there.

[Spork Schivago]

Re: Need help identifying value of this bad SMD cap.

Is it possible that there's more than just two layers here? I use my needle probes and I put them on that hole next to the bad cap. Then, on the other side, I've tried every hole around there and I can't get any readings at all. But if I have one of my probes on that hole and test the continuity to a capacitor or resistor, I get continuity. Really high resistance though, like .405 Megaohms. So I'm certain my needle probes are small enough to get into the hole...

[Spork Schivago]

Re: Need help identifying value of this bad SMD cap.

Pulled the little tiny resistor and measured it at 393 Ohm. I'm guessing it's supposed to be a 400 ohm resistor. Gonna try getting it back on. It's really, really, really tiny. Never played with suuuuchhhh a small resistor. There'd be no way to hand solder it because of how small it is. Even the tip on my micro soldering iron is a lot bigger than this whole resistor. The pads I can barely see. Gotta use a magnifying glass.

[budm]

Re: Need help identifying value of this bad SMD cap.

Test in Diode mode both directions of the probes.

[Spork Schivago]

Re: Need help identifying value of this bad SMD cap.

Test in Diode mode both directions of the probes.

My DMM doesn't have a Diode mode Budm. It's a very old Craftsman True RMS DMM. It's Craftsman True RMS AutoRanging Digital Multimeter, 82357

Here's a link to the one I have:
http://www.machine--tools.com/By-Typ...ter-82357.ASPX

[Spork Schivago]

Re: Need help identifying value of this bad SMD cap.

In Ohm mode though, with black probe on D (C), I get
D (C) -> G (B) = 20 Megaohms, slowly counting down
D (C) -> S (E) = 60 KOhms, slowly counting down

With red probe on D (C), I get
D (C) - G (B): 0.43 Megaohms, slowly counting up
D (C) - S (E): 143.2 KOhms, but it was higher, jumping around a bit, and finally stayed at 143.2 KOhms.

With black probe on G (B) and red probe on S (E), I get 0.403 Megaohms.
With red probe on G (B) and black probe on S (E), I get 28.75 Megaohms, slowly counting down.

[budm]

Re: Need help identifying value of this bad SMD cap.

The Ohms mode so far showing it is not shorted out, you need diode mode to test the PN junctions.

[stj]

Re: Need help identifying value of this bad SMD cap.

too bad i cant make out the writing in those foto's
i refuse to believe that a meter with true-rms and a serial interface is lacking a diode test.