SMT caps question

[Ken_B]

I haven't worked with SMT's much, and have been trying to learn about the
codes. However I can find no information on the small caps that have no
printing on them whatsoever. The only variation I can detect between them is
slight variations in color, and some variation in thickness.

How does one determine the value of these caps?

Thanks.

 

[Roger Gt]

: I haven't worked with SMT's much, and have been trying to learn
about the
: codes. However I can find no information on the small caps that
have no
: printing on them whatsoever. The only variation I can detect
between them is
: slight variations in color, and some variation in thickness.
:
: How does one determine the value of these caps?
:
: Thanks.

A meter?

Some are marked, but in code, all are best read by a meter.

 

[Spehro Pefhany]

I haven't worked with SMT's much, and have been trying to learn about the
codes. However I can find no information on the small caps that have no
printing on them whatsoever. The only variation I can detect between them is
slight variations in color, and some variation in thickness.

How does one determine the value of these caps?

Thanks.

Read the label printed on the reel.

Best regards,
Spehro Pefhany

 

[David L. Jones]

I haven't worked with SMT's much, and have been trying to learn about the
codes. However I can find no information on the small caps that have no
printing on them whatsoever. The only variation I can detect between them is
slight variations in color, and some variation in thickness.

How does one determine the value of these caps?

Thanks.

The small ceramic caps don't have any codes on them at all. The only
way to tell the value is to measure it.
Once it leaves the bag or reel it came in you loose all track of the
value. A good reason not to have more than one type open and on the
bench at any one time while hand soldering!

Dave

 

[Ken_B]

So if one of those caps is bad, I'm out of luck without a schematic.

I'm not a technician, just a hobbyist, and I'm trying to repair a device
with an open smt cap. Does the variation in shade of color mean anything?

I'm thinking I could infer the capacitance of the open one by measuring one
that looks identical.

Thanks for the replies.

 

[Walter Harley]

So if one of those caps is bad, I'm out of luck without a schematic.

I'm not a technician, just a hobbyist, and I'm trying to repair a device
with an open smt cap. Does the variation in shade of color mean anything?

I'm thinking I could infer the capacitance of the open one by measuring
one that looks identical.

No, you cannot. My parts bins are full of SMT caps that cover a six decade
range of capacitances and that all look exactly identical. Variation in
shade probably means the caps came from different manufacturers or different
manufacturing batches. Which might mean different values or different
dielectrics; or it might not.

You might be able to infer the capacitance from figuring out what the
capacitor is doing in the circuit, even without a schematic. For instance,
if it's between a supply pin of an IC and ground, it's a bypass capacitor,
and 100nF is a likely value. If it's in a value-critical part of the
circuit, though (e.g., something that determines frequency), you're out of
luck. Unless it's in a stereo, in which case you might be able to find a
corresponding cap in the other channel.

 

[Tim Shoppa]

So if one of those caps is bad, I'm out of luck without a schematic.

I'm not a technician, just a hobbyist, and I'm trying to repair a device
with an open smt cap. Does the variation in shade of color mean anything?

I'm thinking I could infer the capacitance of the open one by measuring one
that looks identical.

Not necessarily... an 0603 cap could be anything from 0.1pF to 4.7uF, a
factor of almost ten million in capacitance.

But figuring out what the cap does (bypass? tuned circuit? interstage
coupling?) will give a better guess as to value(s) than just physical
dimensions.

Did the old (bad) cap crack in two, delaminate, blow up?

And maybe it wasn't even a cap... there are unmarked SMT resistors, diodes,
and fuses, too. (Diodes have a polarity but as long as they put the
tape and reel in the right way, the polarity doesn't have to be marked.)

Tim.

 

[Ken_B]

A nearby IC blew up. I measured the caps and resistors around it and all
seemed ok except no reading on one cap (had a C number next to it).

While they are miniaturizing everything, they should work on teeny-tiny
markings that a person could read through a magnefying glass!

No biggie, just some junk I thought I'd try to fix. Modern technology sure
is making that harder to do, huh?

 

[Tim Shoppa]

A nearby IC blew up. I measured the caps and resistors around it and all
seemed ok except no reading on one cap (had a C number next to it).

Testing components in-circuit isn't always reliable. While it's a bad
thing that a "IC blew up" and it's possible that a cap failure is
related (cause or effect), I still think that you have to understand what
that capacitor is there for before you can start guessing values or
reasons.

While they are miniaturizing everything, they should work on teeny-tiny
markings that a person could read through a magnefying glass!

No biggie, just some junk I thought I'd try to fix. Modern technology sure
is making that harder to do, huh?

12-layer PCB's don't make it any easier to trace the circuit

Tim.