These are pretty old 'scopes now (have one, only it's
TDS3054, not DPO3054). You might be better off looking
for "for repair" busted ones that purport to have working
power but some other issue.
What service manuals say, and what's really wrong, do
not necessarily relate. Start with why the power supply
is not putting out, is my advice. Fuse? Back panel tamper
switch? Fried PWM chip down in the guts? You might get
lucky chasing repair schematics on the Web if you get
the keywords right (like, maybe omit all of those spaces
one time and see if results get more useful).