waveform problems on oscillator circuit

2 years 6 months ago #29535558 by Harold123
Part Number:  SN74AHC1G04
Other Parts Discussed in Thread:  SN74LVC1GU04  Hi: all, sorry I post two as there is something wrong in the first one but i  did not find the delete button.
Here is the new one.
i'm working on an old board on which a pierce oscillator circuit is mounted: 
Quartz Crystal is TQX6800/A Nominal frequency 9,0316 MHzC42 C0805C479C1GACTUC43 C0805C120J1GACR74 R75 R66 smd resistor.The problem i've been having these days is that a normal waveform on the output of SN74HC1G04 shows some distorsions as you can see below (purple trace on right figure).

 Most of times the problem is solved by replacing the inverter IC with one in another reel. Sometimes it is solved by adding capacitance in parallel to C42.Could you help me What could be due to the malfunction?Let me know.

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