I got my DSO138 several months ago, apparently based on all the signs it was an original one. The version I have had the SMDs already soldered on the board, and I only had to solder the through-hole components.
Once I got everything together and powered it up, the test-point voltages were a little bit off (4.0V instead of 3.3V, and 4.5V instead of 5.0V, etc...) but I didn't think its something to be worried about. When the scope worked, it didn't have any special problems with measuring - but the screen had lots of flickering and white lines on the top.
Lots of white lines, the faster the signal - more lines, etc... Lately I needed to use the scope and this problem really bothered me, so I went searching for similar posts and videos on youtube but couldn't find anyone mentioning it before.
Since I am just a beginner with electronics, it took me the past half year to learn why such a problem might occur. Especially since last week I was playing around with a 3.3V TFT screen - this made me realise that the 4.0V on the top +3.3V test point has something to do with the 1117-3.3 regulator. I tested the regulator a bit more closely, and indeed it would seem it returned 4.0V instead of 3.3.
The fix for this problem was desoldering the SMD AM1117-3.3 regulator, and replacing it with a new one. Luckily I had a whole bunch of these laying around. This fixed the problem completely, now the screen looks great and has no flickering - and the white lines are gone as well. This and the latest firmware upgrade remove the amount of noise on the scope as well in my opinion.
So just wanted to put this out there, if anyone else finds that the 3.3V point is returning more voltage than it should -- try and check if the voltage regulator has problems. I got my board with these already soldered on it, so I assumed it was okay, but assumptions are the root of all problems.
Hope this helps someone. Cheers!
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