40khz Crystal Oscillator Problem

[mvilla]

Hello everyone, I have a problem with a 40kHz oscillator that I am building with a crystal. My problem is the stability of the signal.
Because although the frequency and amplitude is correct, the signal is unable to maintain a zero or reference line, as this all the time jumping all the signal from positive to negative.
If anyone knows how I could fix this I'll be very grateful. defase since this signal, I also moved to the driver of ultrasound transducers.

regards
and thanks!

diagram:
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Video Signal Oscilloscope
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[MikeMl]

It looks like it is beating with the 50/60Hz power line frequency. How is the scope connected to the circuit, particularly the scope ground?

 

[mvilla]

hello, I use a laboratory power supply. But I've also used a 9v battery. and occurs the same effect. : (

 

[ericgibbs]

hello, I use a laboratory power supply. But I've also used a 9v battery. and occurs the same effect. : (

hi,
How are the two spare inverters in the IC, connected.?? any unused inputs should be grounded.

 

[MikeMl]

Is the scope analog, or a digital sampling scope?