Just TomC has concentrated to psu board, I am thinking to focus to the adapter board.
I don't have the time to make a schematic for all this board but I'll search some dc-dc convertors, difference btw Ver 3.0 and 3.2 and so on.
At the first I am looking the AOZ1094AI dc-dc convertor that produce the 5.5V.
What Owon makes at the the two versions? Look at the attachment photo (left is 3.2, right is 3.0 version).
At the version 3.2 corrects the badly cutting of gnd that previous was made (point 1). Removed the smd capacitor C36 (point 2), adding a second inductor 5.6uH with some smd decoupling capacitors (point 3). The changes was few and very easy to make but is that according to AOZ1094 datasheet?
The next schematic is from datasheet of convertor, a general proposal for 3.3V output. For 5V output the factory suggests L1=5.6uH, Rc=31.6KOhms, Cc=1nF.
For what reason the Owon uses two 5.6uH inductors? For what reason has made mods by hand on version 3.0 with adding a 10uH inductor? Of course was the eliminate the noise but what are they compute.... ?
If you looking more carefully at the schematics, missing some components!
Where the C5=1000pF capacitor that joined the AGND and Enable?
Where is the parallel to diode Rs and Cs components?
At the output the factory suggest two 22uF electrolytic capacitor or some combination : "For lower output ripple voltage across the entire operating temperature range, X5R or X7R dielectric type of ceramic, or other low ESR tantalum or aluminum electrolytic capacitors are recommended to be used as output capacitors."
Have all these in my mind I'll make a check again and I am going to follow the datasheet...
Please, if someone looks the values of smd resistor R18, R19, R20 and R21 on Version 3.2