18V25 no 3.3V no lights 5V is there

For the simple motor controllers, does anyone know which IC is the 3.3V regulator as I think I fried this part…I have the 18V25. With USB or with 20V supplied, I see no leds at all… but the 5V is still active so I’m wondering if the 5V to 3.3V regulator is all that is blown (assuming that is where the 3.3V comes from). The 5V actual value is about 4.7V with either USB or 20V as the supply. The 3.3V actual value is about zero.

Hello, Lowell.

I am sorry you are having trouble with the Simple Motor Controller.

The 3.3V regulator is the 5-pin part right next to the USB connector. If you measure 3.3 V on the pin labeled “3V3”, that would mean the regulator is working. If you measure a significantly lower voltage on that pin, then it could either be the 3.3 V regulator’s fault or it could be the fault of another component on the board which is drawing too much current. Be careful; the 3.3V regulator might get hot when you apply power!

If you give us more information about your system and tell us what you were doing just before it stopped working, we might be able to figure out what went wrong.


Hi David,
I connected an external power supply (5V) to the 5V pin on thi 18V25 to eliminate some crosstalk issues. This worked fine until I accidently connected this 5V pin to a higher voltage and all went dead. After writing the above post, it occurred to me to try to supply the 3.3V from an external power supply which I tried yesterday and in doing this, all seems to work ok. So I could just use my own regulator to bring the 5V down to 3.3V (such as using an lm317 which I have on hand). Or I could just buy the correct 3.3V regulator if I knew the correct part number. I spent hours looking for the id of the part, based on the marking on the package (AG3D). But I never found this exact marking. Then there is Pin 4 which is troubling as I do see a voltage present on that pin on the 18V25 so I bet the part is similar to On Semi part NCP700B which has pin 4 used as a “bypass”. Anyway, if you can tell me the part, I will replace it myself… otherwise, I’ll do a 3.3V regulator of my own… I have the room.
Thanks very much for taking the time to reply.

The 3.3 V regulator is the FAN2504S33X. There are many similar regulators with the same pinout. On the PCB, there is a 2.2nF capacitor between GND and the bypass pin, and there is a 4.7uF capacitor between GND and the output pin.


Hi David, thanks very much for the info. I should be able to repair this easily now. I like your company and products.