SMD Capacitor value

Guest
Hi all,

Can anyone tell me if there is a way of determining the value of an
unmarked SMD capacitor? Silly question, I know.
The device is about 1.5 x 1.5 x 1mm, it's yellow. I can only imagine
the value could be guessed at by it's physical size.

It's out of a series LRC oscillator circuit for the fill sensing in a
Fisher and Paykel IW708 washing machine (so getting a circuit diagram
is probably not possible) and its o/c. The circuit is a 5V supplied
74HC04 and the oscillator wouldn't until the cap was changed.

So far guessed at .22uF, but this is too large. Trial and error seem
to be the best bet at this point. The L goes up with water level, as
does the frequency of the circuit, so I'll have to drop the
capacitance value as it's overfilling. (i.e. correct frequency never
reached)

Any circuit advice would be appreciated, I've already had all the
advice I need on F&P washing machines in general. It's either fix it
or buy a new machine, and fixing is the cheaper option at present.

I had the darn thing fail three year ago with exactly the same
symptoms, got the F&P man out for a total of $270 to change out the
control board. I kept the old one, with the identical fault (bad batch
of caps?) and it'll be fixed as well, I hope.

TIA

- Rob.
 
<r@r.r.com> wrote in message
news:atsn42pto5vnts5ehmg6t1knttg58gqr70@4ax.com...
Hi all,

Can anyone tell me if there is a way of determining the value of an
unmarked SMD capacitor? Silly question, I know.
The device is about 1.5 x 1.5 x 1mm, it's yellow. I can only imagine
the value could be guessed at by it's physical size.

It's out of a series LRC oscillator circuit for the fill sensing in a
Fisher and Paykel IW708 washing machine (so getting a circuit diagram
is probably not possible) and its o/c. The circuit is a 5V supplied
74HC04 and the oscillator wouldn't until the cap was changed.

So far guessed at .22uF, but this is too large. Trial and error seem
to be the best bet at this point. The L goes up with water level, as
does the frequency of the circuit, so I'll have to drop the
capacitance value as it's overfilling. (i.e. correct frequency never
reached)

Any circuit advice would be appreciated, I've already had all the
advice I need on F&P washing machines in general. It's either fix it
or buy a new machine, and fixing is the cheaper option at present.

I had the darn thing fail three year ago with exactly the same
symptoms, got the F&P man out for a total of $270 to change out the
control board. I kept the old one, with the identical fault (bad batch
of caps?) and it'll be fixed as well, I hope.

TIA

- Rob.
Click to expand...
Peak Atlas make an LCR meter with digital readout - but its rather expensive
at about Ł80 still its a very handy piece of equipment. You can also buy an
add on lead/probe kit which includes a special pair of plastic tweezers with
contact tips for SMD chip components - Peak Atlas just keep on taking at
about Ł35 for the add on kit!
 
r@r.r.com wrote:
Hi all,

Can anyone tell me if there is a way of determining the value of an
unmarked SMD capacitor? Silly question, I know.
The device is about 1.5 x 1.5 x 1mm, it's yellow. I can only imagine
the value could be guessed at by it's physical size.

It's out of a series LRC oscillator circuit for the fill sensing in a
Fisher and Paykel IW708 washing machine (so getting a circuit diagram
is probably not possible) and its o/c. The circuit is a 5V supplied
74HC04 and the oscillator wouldn't until the cap was changed.

So far guessed at .22uF, but this is too large. Trial and error seem
to be the best bet at this point. The L goes up with water level, as
does the frequency of the circuit, so I'll have to drop the
capacitance value as it's overfilling. (i.e. correct frequency never
reached)

Any circuit advice would be appreciated, I've already had all the
advice I need on F&P washing machines in general. It's either fix it
or buy a new machine, and fixing is the cheaper option at present.

I had the darn thing fail three year ago with exactly the same
symptoms, got the F&P man out for a total of $270 to change out the
control board. I kept the old one, with the identical fault (bad batch
of caps?) and it'll be fixed as well, I hope.

TIA

- Rob.
Click to expand...

I've had similar units: MW059, with a sticker marked: Level sensor
calibrated. They appear to have some kind of software calibration for
individual units. Personally, I swapped sensors between a working
board and one with a different fault had problems with over filling.
 
r@r.r.com wrote:

Hi all,

Can anyone tell me if there is a way of determining the value of an
unmarked SMD capacitor? Silly question, I know.
The device is about 1.5 x 1.5 x 1mm, it's yellow. I can only imagine
Click to expand...
Most of the yellow smd capacitors I have seen are tantalums, however
most of them are much larger than yours usually atleast 2-4 mm. They
have a brown stripe at one end to mark the + polarity. And they are big
enough to have the value written on them.


the value could be guessed at by it's physical size.

It's out of a series LRC oscillator circuit for the fill sensing in a
Fisher and Paykel IW708 washing machine (so getting a circuit diagram
is probably not possible) and its o/c. The circuit is a 5V supplied
74HC04 and the oscillator wouldn't until the cap was changed.

So far guessed at .22uF, but this is too large. Trial and error seem
to be the best bet at this point. The L goes up with water level, as
does the frequency of the circuit, so I'll have to drop the
capacitance value as it's overfilling. (i.e. correct frequency never
reached)

Any circuit advice would be appreciated, I've already had all the
advice I need on F&P washing machines in general. It's either fix it
or buy a new machine, and fixing is the cheaper option at present.

I had the darn thing fail three year ago with exactly the same
symptoms, got the F&P man out for a total of $270 to change out the
control board. I kept the old one, with the identical fault (bad batch
of caps?) and it'll be fixed as well, I hope.

TIA

- Rob.
Click to expand...
 
On Mon, 24 Apr 2006 22:39:19 +1000, andrew Gamlen
<andrewgamlen@chainyahoo.com.au> wrote:

r@r.r.com wrote:

Hi all,

Can anyone tell me if there is a way of determining the value of an
unmarked SMD capacitor? Silly question, I know.
The device is about 1.5 x 1.5 x 1mm, it's yellow. I can only imagine

Most of the yellow smd capacitors I have seen are tantalums, however
most of them are much larger than yours usually atleast 2-4 mm. They
have a brown stripe at one end to mark the + polarity. And they are big
enough to have the value written on them.


the value could be guessed at by it's physical size.

It's out of a series LRC oscillator circuit for the fill sensing in a
Fisher and Paykel IW708 washing machine (so getting a circuit diagram
is probably not possible) and its o/c. The circuit is a 5V supplied
74HC04 and the oscillator wouldn't until the cap was changed.

So far guessed at .22uF, but this is too large. Trial and error seem
to be the best bet at this point. The L goes up with water level, as
does the frequency of the circuit, so I'll have to drop the
capacitance value as it's overfilling. (i.e. correct frequency never
reached)

Any circuit advice would be appreciated, I've already had all the
advice I need on F&P washing machines in general. It's either fix it
or buy a new machine, and fixing is the cheaper option at present.

I had the darn thing fail three year ago with exactly the same
symptoms, got the F&P man out for a total of $270 to change out the
control board. I kept the old one, with the identical fault (bad batch
of caps?) and it'll be fixed as well, I hope.

TIA

- Rob.

Most SMD capacitors do not have a value on them except the tantalums.
Click to expand...

Why not leave the oscillator not working and inject a frequency from a
signal generator to find what frequency you need to represent a full
machine. Once you know the frequency then you can select the
appropriate cap.

Otherwise start with a much lower value of C and work up till you find
the right one.

Alan

--
Sell your surplus electronic components at
http://ozcomponents.com
Search or browse for that IC, capacitor,
crystal or other component you need.
 
Thanks for all the replies, it turns out that the capacitor was only
there for de-coupling. It's value had no effect on frequency. Changed
it for a 0.1uF and all is back to normal. Now have a working spare
control board as well.

- Rob.
 
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