SMD Capacitor value

[[email protected]]

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.

 

[Mark Harriss]

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.

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.

 

[andrew Gamlen]

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.

 

[[email protected]]

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.