by johng » Sat Aug 05, 2017 4:05 pm
My experience...
Firstly:
1) When I compare circuit diagrams (older vs newer boards), this portion of the
circuit is exactly the same, with same values. I expect tuning to have similar
results for both boards.
2) I have an older board, dated 2016, with #54 firmware. There is a known bug
to do with reading the test signal with this firmware version, so I used an AC
(not DC) connection.
What I saw (using a 'scope probe set at 1X):
C3) (0.1V test)
When I play around with C3, I can modify the waveshape to have rounded corners,
and I can easily bring it back into square shape.
C5) (3.3V test)
Adjusting C5 made no difference to the waveshape, but the waveshape is already a
fairly clean square (with a bit of overshoot) anyway. I got curious as to whether
changing C4 to the pigtail trimmer would make a difference -- it didn't, as far as
having C5 be able to modify the waveshape. I used #30 wirewrap wire, and actually
started with approx. 6cm length, for good measure. However, it did introduce
significant overshoot, until I cut it quite short.
Final test...
I untwisted the 0.5cm wires so they were standing separately -- adjusting C5 made
no difference, and there was no difference in the waveform, so I didn't bother taking
a picture.
YMMV,
John
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