Voltage reading problem

[miki]

Hello everyone,
I am new in the world of electronics (only hoby), this is my first scope

I have assembled and soldered everything according to the guidelines, rechecked things couple times, everything seems to be in normal. Voltages references (V+, V-, V1... etc) seem to be ok.
I also went through troubleshooting, H-L levels are ok.

What i have problem with are voltage readings for test signal. 1kHz is displayed, but voltage levels depend on voltage scale selected.
PS. It also seems that whether test signal is activated or not (by pressing ADJ for 3 sec), test signal is in output.

I have tried to combine everything in one picture, if it is problematic to see i will change.
You see, depending on voltage scale selected, Vmax is displayed. And it should be 0.1V . And for 1V and bigger, frequency is not displayed.

I am not so strong in electronics, so i would appreciate any help, where to look and what to check.

(Version is 113-15001-111) ordered through banggood on 16. january and received it yesterday.

Thanks in advance,
Miki

[miki]

If T.S. Amp is 0.1V , shouldn't Vmax be also 0.1V (in any voltage scale (Vpos) - 5mV, 10mV, 20mV...)?

Instead i get (from pictures):
Vpos: 5mV - Vmax: 24mV
Vpos: 10mV - Vmax: 49mV
Vpos: 20mV - Vmax: 99mV <- good one?
Vpos: 50mV - Vmax: 249mV
Vpos: 0.1V - Vmax: 0.49V
Vpos: 0.2V - Vmax: 0.98mV
Vpos: 1V - Vmax: 0.36V
Vpos: 2V - Vmax: 0.73V
Vpos: 5V - Vmax: 1.82V
Vpos: 10V - Vmax: 3.65V

[jye1]

There are a couple of factors that cause the reading errors. The most significant is the scope background noise. This noise is independent of sensitivity setting. So when sensitivity is set to low (like 5V, 10V, etc) the noise will cause large reading error. You can compare by setting couple to GND and changing sensitivity from 5mV to 20V. You will see its difference.

The second factor is the error in the gain of analog channel. I couldn't verify this since the photos did not have complete amplitude displayed. We can check it if you post a waveform with complete amplitude within screen.

Another factor that cause the error is the VPos offset if it is not cleared. You need to perform VPos alignment (by holding V/DIV button for 3 seconds) to clear it.

[miki]

Thank you for response!

I made a video, so it is easier to see all levels in different sensitivity.
From 0:00 to 0:34 is noise level (as you explained it to me, set to GND and go through 20V to 5mV).
From 0:45 starts DC settings, also from 20V to 5mV, with T.S. Amp set to 0.1V .

https://www.youtube.com/watch?v=6zdtqL2V_0w

I rechecked resistors on the board, everything seems to be ok (except R3 is 1.0M instead of 1.2M).
I am very close to resolder all of them, but would like to check if problem can be somewhere else.

[jye1]

The video is too small. I couldn't see it clearly. But I saw that the 3.3V test signal appeared only about 1V on screen at 1V/div scale. This is incorrect. However, the displayed amplitude matches the voltage reading. This indicates the analog gain might be wrong.

[RobNL]

Not connect ?

[miki]

I connected with yellow cable directly to the pin soldered to the board (same happens with provided connector, this was debugging )

@jye1 gave me direction to think about. From 20V to 0.5V resolution, voltage function drawn is only one square high (not 3.3V or 0.1V, but one square any time), but reading is good (1 square at 20V resolution is measured as 20V, 1 square at resolution 2V is measured as 2V...). So i am rechecking all resistors and analog gain once more.

Another problem happens below 0.5V resolution, because voltage function jumps out of bounds, as on video.
I am checking the scheme, but don't have experience so it takes time

If i still have problem, i will record video one more time with better resolution.

PS. If anyone has any advice or suggestion, i am ready to hear

[miki]

I have checked with magnifier all solder joints, and it turned out that i have few bad ones. Inexperience
After resoldering, everything seems to be working now.

Thank you for you time and for your help!