I am trying to figure out an issue that I have with LM317 regulator.
It is producing ~ 1.7V at VOUT instead of desired 5V.
I've used this design in several other PCBs with no issues.
The schematic is following:
The layout from both sides:
Couple of observations:
- Vin measures stable 12V at first pin of LM317 as well as other places of the system - F1 fuse is not damaged (measured resistance between pin 5 of J7 and pin 1 of U10 is 0.9Ohm)
- Voltage at ADJ pin is ~ 0.4V while powered on
- There is no short between VOUT and GND: measured resistance is 898Ohm as expected - individual resistors R31 and R32 also measure according to the schematic
- 5V is connected to supply of several of CMOS ICs each of which has 0.1uF capacitor near its power supply - none of the ICs are heating while powered on
- Replacement of LM317 with brand new IC did not produce any observable change
I would appreciate if you could point out what may cause this behavior in my prototype and what additional measurements I should do.