I'm repairing owon pds5022 where the power supply is bad. The U3 chip is
burn beyond any real markings. It is 5 pin smd, SOT-25 package.
I've drawn the schema on paper and it looks like pin3 is input ( fed via
resistor), pin2 is ground, pin1 could be feedback. Pins 4&5 are
connected together and act as output, there is also connection to pin1
to connector with small condensator and inductor.
The markings are so small that I cannot read them even with magnifier
glass (I'm getting old:-( ) , need stereomicroscope to read them.
The U3 could have markings 510B but cannot tell if that's correct.
The B can also be some manufacturer logo, code could also be upside down.

I've ruled out a couple smd regulators ( Torek brand ) , any idea what
component could really be ? Owon has not answered to my query.

ismo