Delayed TOS screen, 15 - 20, amidst "burps" undoubtedly the floppy trying to read (it's empty). It stays on for a while, then reboots and starts the shenanigans all over again! My mashoogunna Atari I call it.
It might be that the one unit that boots fast has a disconnected drive? It's bouncing around inside. I'm just amazed and elated both work. Now I can pull the p/s from one of these and test my 1040stf and that French 520st Mobo.
The cutouts for the drives differs between the two.