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SMD Capacitor value

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.

Reply to
r
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Peak Atlas make an LCR meter with digital readout - but its rather expensive at about £80 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 £35 for the add on kit!

Reply to
I.F.

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.

Reply to
Mark Harriss

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.

Reply to
andrew Gamlen

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

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

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Reply to
Alan

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.

Reply to
r

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