Hi there,
i have an AP66300 (A) that gives me a 5V from 14V. After that i got a regulator (R)(MCP1703) that puts out 3.3V, but these 3.3V have some kind of noise (pretty exact 400Hz) (is that terminology right?).
On that 3.3V i got a few components, that are on the pictures. Not to forget the uC, but which i disabled via reset.
I think i can rule out the can (C) unit, since i do not measure a corresponding signal over R727, just a regularly signal. The same applies to pin 1 to gnd on that unit.
For the Hallsensor AH1913 (H), i put a magnet over it, which did not change anything.
I got also an oscillator (O) on the 3.3 rail with 24Mhz, but i dont think it would make a noise that has 400Hz?
That EEPROM (E) is on the other side of the board, and i cant access it.
When i turn off the board (not disconnect plus or minus), the noise is gone.
The AP66300 and the regulator are 15mm apart, and the rest is on average 50mm away. In between there is nothing.
Probing around with a spring loop, did not show a source of this noise. Nor did a holding the tip on those.
Docs:
https://www.diodes.com/assets/Datasheets/AP66300.pdfhttps://ww1.microchip.com/downloads/en/DeviceDoc/22049f.pdf (MCP1703)
https://ww1.microchip.com/downloads/aemDocuments/documents/MPD/ProductDocuments/DataSheets/24AA32A-24LC32A-32-Kbit-I2C-Serial-EEPROM-DS20001713.pdfhttps://ww1.microchip.com/downloads/en/DeviceDoc/20001667G.pdf ( CAN MCP2551)
https://www.diodes.com/assets/Datasheets/AH1913.pdf