C5 has no effect

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Bobmoo79
Posts: 4
Joined: Thu Jan 04, 2018 10:06 pm

C5 has no effect

Post by Bobmoo79 »

Hello all,

Just checking in because I have a problem with the DSO Shell kit (SMD pre-installed).
After solving an issue with the rotary control (my fault completely) I've found that I cannot calibrate the scope properly. With the 1.1v test signal I am able to adjust the shape using cap C3 without a problem, but when I set the test signal to 3.3v I find that C5 does nothing at all. I have given the board the once over but can't see anything wrong so I wondered whether you guys have seen thisproblem before.

I should also say that the 3.3v text signal actually looks pretty good without adjustment (see picture) but rather than being a comfort it makes me more suspicious that something strange is going on!

Anyway, any help you can give would be appreciated.

Thanks (in advance)

Image
robocog
Posts: 64
Joined: Tue Sep 12, 2017 10:06 am

Re: C5 has no effect

Post by robocog »

Both mine are the same - but just as in your case - the signals are fine and do not need adjusting any (thankfully!)

Regards
Rob
Bobmoo79
Posts: 4
Joined: Thu Jan 04, 2018 10:06 pm

Re: C5 has no effect

Post by Bobmoo79 »

Well at least it's not only me! I could just live with it I suppose but I'd rather get to the bottom of it if I can
Bobmoo79
Posts: 4
Joined: Thu Jan 04, 2018 10:06 pm

Re: C5 has no effect

Post by Bobmoo79 »

bumping because I would still like some help with this...

Jye, any ideas??
RobNL
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Joined: Mon Dec 25, 2017 3:11 pm
Location: The Netherlands
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Re: C5 has no effect

Post by RobNL »

CU, Rob
LupinIII
Posts: 6
Joined: Wed Jan 10, 2018 8:19 pm

Re: C5 has no effect

Post by LupinIII »

Although the square wave was fine for me to begin with (E version of the analog board), C5 does change the signal for me, but it is very subtle, if you have a full period of the square wave on screen. The change is about 2pixel in height visible for the first pixel of the corner of the square wave. It goes from one pixel "undershoot" to 1 pixel "overshoot". Did you ever zoom in when doing the probe calibration? There's no need to have a full period of the square wave on screen. It is only the edge that's important. The change is much more visible there.
Bobmoo79
Posts: 4
Joined: Thu Jan 04, 2018 10:06 pm

Re: C5 has no effect

Post by Bobmoo79 »

Thanks for the help guys, I'll get the Shell out again tonight and have another go at fixing this issue.

LupinIII I never zoomed in, I just used the display settings stated in the calibration procedure. I'll try changing the V/div and time settings to see if there is just a minor change in the waveform as you described.

RobNL, thanks for link. I thought I had checked the FAQ but I guess not! I'll try the twisted wire method and see how it goes.
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