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STM32F405 Won't Oscillate ?!?

Question asked by roofie01 on Jun 15, 2015
Latest reply on Jun 16, 2015 by roofie01
Hello:

This problem has me totally dumbfounded. Please see the attached image and screen shot of schematic. An absolutely simple circuit, yet it does not want to oscillate. This is the second board (different PCB, different mfr) so it's not that, or parts. So what does that leave?  I have made the identical circuit before, and in fact just copied the micro schematic page and used that. So this is really difficult to understand...I have:

-checked every pin's connectivity, and adjacent pins for shorts
-every Vdd has a cap
-vcap1, and vcap2 are installed, and show 1.23V when 3.3V is applied to the board.
-the oscillator circuit is identical to the Discovery board. Resistor is 220 ohms, caps are 20pF, and oscillator load is 20pF

Yet....the oscillator is silent. Unexplainable...can someone please provide a clue as to what is going on? Any tips on what I can do to determine what is going on?

BTW - have tried scope with both AC/DC coupling, probe at 10x

Thank you...




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