Black Screen iMac G4 - Tried multiple things

PS: depending on which exact build series iMac G4 -between 700MHz through 1.25GHz- one has

Here's online linked PDF version 'service manual copy' Last iMac G4 USB2.0 ~ for 1.0 - 1.25GHz..

Another link to original content:

Has nice images and details for this model series from 2003.

• Resetting the iMac (Flat Panel) Power Management Unit (PMU) - Apple Support

https://support.apple.com/en-us/HT1712

[..thermal paste and iMac G4 repair - search result duckduckgo..]

{..older iMac user guides & 'power management resets' info + locations : weebly + X-labs..}

One of the things to Avoid, would be to try to disassemble the Chrome Arm. There are

no user-servicable parts inside ~ just big springs and most difficult bits to put back in.

I used to have more information for 1.25 model, & still have three complete IN-OP ones.

While you had the base unit open, did you install a new '1/2AA 3.6V Lithium' clock battery inside?

One of the symptoms of you state (black screen) has been known to relate to failed clock battery.

There are other potential causes to the symptom, in the circuitry for display; both power and data.

Any wires loose? Connectors not snug? Fusible links?

You may be able to locate online a source for original Apple Service Manual in PDF (or published

original for use by tech, in addition to digital copy) for USB2.0 iMac G4, or earlier models. You may

be able to see one online from powerbookmedic.com, or ifixit; some still had repair manuals.

Good luck & happy trails!🌞🍀