C5 calibration on new version

[jan]

Forum , Jye ,

What is the best workaround/solution to get C5 calibration working ??

on my board ( yes , this time a genuine one new version with latest firmware ) C5 is not changing anything when calibrating 3.3 V signal as described in the manual .

C3 calibration works spot-on.


Please advice .



jan

[johng]

When you say "new version", do you mean the recent board revisions?
I think this should still apply: the "FAQ, Tips, and Troubleshooting" post, pinned at the top.
There is a subsection "Calibrating C5 and C3"

If yes to the revised board, where did you get it?

[jan]

Indeed the new version .

i was wondering if there are forum user who are facing the same problem and wiggled around with the suggested options by jye ?

i bought my kit from Banggood and it turns out to be genuine.

[jan]

unfortunately ,


i have replaced C4 with the suggested 3cm awg28 twisted wire BUT , no change in the adjustments of C5 the screen remains the same ( no change in wave-form at all ).

i have tested without C4 and with the full 3cmm twisted.............

anyone with experience on this matter ??


jan

[jye1]

Can you post how the waveform look like without C4?

[johng]

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

[alphaseek]

John, I have the same board and firmware as you. Looking at the schematic, it seems that the input signal flows through two paths, one adjusted by C3 and the other adjusted by C5. The one being selected is chosen by the state of SENSEL3, which selects the output of the 74HC4053 from the two inputs.

I don't know what SENSEL3 is, but it seems that if C5 has no effect on the display, it may be because even at 3.3V the state of SENSEL3 still hasn't switched. So you're adjusting C5, but the input being selected is still the one adjusted by C3.

Has anyone compared the state of SENSEL3 when making these adjustments? When adjusting C5, it should be the opposite state from when adjusting C3. What I'm asking is whether .1V and 3.3V are within the same SENSEL3 state rather than opposite ones.

[jan]

Alphaseek ,


Your conclusion could be right , according to jye1 this should be the sensel table .

[johng]

@AlphaSeek - thanks for the pointer.

>> So you're adjusting C5, but the input being selected is still the one adjusted by C3.

That makes sense, but, If this is the case, then I think adjusting C3 should have some effect on the shape of the 3.3V signal, shouldn't it? (It didn't.)


>> Has anyone compared the state of SENSEL3

Just tested it: The state doesn't change. Using a DVM, I measured 0.003 - 0.005V.(Reading taken at pin 11 of U2 (the 74HC4503) on the Analog board.)


>> I don't know what SENSEL3 is

I traced SENSEL3 back to pin 14 of the STM32 chip on the main board (it goes through the 5x2 header that connects the 2 boards). So, I *think* that when we set the input sensitivity (50mV, 0.1V, etc), then the STM32 is supposed to set SENSEL3 according to values in the SENSEL table.

---

I tested the SENSEL3 state at the 74HC4503. It would be useful to test back at pin 14 on the STM32, to verify that there is continuity. I'm just not sure how to get at that point/pin with everything connected. Anyone have ideas?

@Jan...
Testing SENSEL3 state on your (newer) board would be useful, too. Again, with everything connected, I'm not sure if/how that can be done.


John

[jan]

i verified that changing the setting of C3 affects both 0.1 and 3.3 waveform.
it is even possible to get both waveforms nice in line with the horizontal grid , but the 0.1 has sharp edges , whilst the 3.3 waveform remains curved .

and indeed on my 2 dso150 units , with the correct settings 3.3 and timing , C5 does not change a thing...............

i also used the wire C4 , but no change to the adjustments to the 3.3 waveform.

as round edges should be indicating a too high value of C6 , i will try to get some caps to test a smaller C6


any futher info highly appreciated