I seem to remember, when playing with oscillators, that there was
a condition that allowed (or perhaps permitted) the oscillator to
run at the wrong frequency.? It may be the drive to the crystal,
and I wonder if the actual VCC to the oscillator is somehow
wrong.? It was a long time ago, relatively, but I seem to remember
something that was stable suddenly running at twice the
frequency.? Since (as I remember the waveform here, zero counting
would ignore the peaks and simply say that it's twice the
frequency).? Might be a bypass cap, a feedback cap wrong, not
sure.? If it were a crystal problem, it almost seems as if it's in
overtone mode.
Harvey
On 3/7/2022 3:06 PM, Jinxie wrote:
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I believe Bruce is referring to the 100Mhz oscillator on A7A2
which is probably a good call to check next.
WRT Ozan's remarks, I would simply confirm it's not a probing
issue in this case. The waveforms are only barely recognizable as
a square wave when intermittently present if at all. In fact the
randomness of the duty cycle looks very similar indeed to that I
saw on HUL2 on A10A6; so much so I'd say they must surely be
related. Checking the power rail in the area of this fault also
looks like a good idea to me in case it's a reg playing up.
