JYE Tech Forum

1) What is the accuracy of your ohmmeter on that range?

I'd just try it. If you really want 20mA through it then (5.0V - 1.85V) / .02A = 150 Ohms. Is it bright enough with the original resistor?

Try removing the trimmers and see what the response looks like. Even mis-adjusting either trimmer the test waveform "over-shoot" on my unit doesn't 0look anywhere as much as yours does. Maybe, a wrong component in the voltage-divider compensation networks.

The green plastic coating looks deformed. Maybe you damaged these parts as you placed them on the PCB.

Unless you answer my question about measuring their capacitance OFF the board I can provide no further help.

Ah, had a closer look at your picture. They looked like they have been "cooked", ie severely over-heated.

I have used this type of trimmer in many products and never seen them display a constant max capacitance value ... under fault conditions. Just to verify ... you have removed the trimmer from the board and while measuring capacitance have rotated the adjustment a full 360 degress?

Both of them? I noticed that the change on C6 is barely noticeable.

Can't think of a reason this would fail. As you seem to be aware you may need to adjust the LED current appropriately.

C21 from a stability point may not be relevant as L3 may be a high enough impedance at the frequencies where it might be unstable. IE, the regulator just "sees" C20 from a stability point of view. One would need to get Pspice or some linear simulator to analyse this. C22 is shown as 100uF ...

So, is the calibration signal always causing the trace to exceed the top and bottom of the screen? Go back to a finger test and see if you can get a trace within the bounds of the screen and then go through the different switch positions to see if you can change the sensitivity. Which firmware versi...