Atari 800XL power issue - Atari NEWBIE

[JoeG]

I'm new to Atari computers, and the 800XL I purchased off of ebay is my first. It was sold, and shown in the listing, as working. Unfortunately, it doesn't now. My intention was to learn about the Atari 800XL before I started to attempt to repair one. Well, I advanced ahead to the learning how to repair one now.

Here's the issue:
- When I plug the male power plug into the Atari 800XL female power port while their is power to the plug, the voltages drop from +5v to zero. Even with the separate power switch off or on.
- The power plug has been checked to ensure that pins 1 and 4 are +5v, and that pins 3 and 5 have a good ground. The other pins are not used. Everything looks good.
- When I connect the male power plug (without power to the plug) to the female power port on the Atari 800XL and check for continuity from the plug pins (by using a small hook clip wire lead between the plug and the power port) and the corresponding power port legs that connect to the PCB, they all have continuity as they should. To restate this, there is continuity from plug pins, the power port female connectors on the Atari, and to the power port legs that connect to the PCB. All good.
- As an aside, I have no video signal as well as a result (not a surprise with no power).

It appears that I have ground short? Not sure. I've never seen anything like this before when I've been repairing Commodore PC's. If it is a ground short, where's a good place to start checking for the short? All the chips are in sockets, so I could pull those if needed.

I'm at a loss on my next step. Any help is appreciated!

Thank you!

Joe