Posted on December 12, 2017 at 11:52U4 shouldn't get hot - it's just a switch, not a linear regulator or anything like that.
How do you apply power?
How have you set the links on JP3?
Does LD6 glow at all? What voltage do you measure on the +5V line (e.g. pins 1,3,5 of JP3)?
Does LD5 still glow if you remove all links on JP3 and then apply power?
It's possible that your board has a short-circuit from a power rail to ground. Possibly a bit of wire or a solder splash.
Or maybe a blown-up chip. As to why it blew up, it could have been from an electrostatic discharge (all semiconductors are vulnerable to a greater or lesser extent) or applying over-voltage or reversed power - even for a tiny fraction of a second.
In a work environment, I'd consider the board as scrap and buy another one. I know that's not a welcome choice for the hobbyist who spent hard-earned/pocket money and has to wait days for a replacement board with the worry that the same thing might happen to it.
Have you had success with other ST demo boards? Do you have access to a known-working set-up?
Sorry I can't be much help,
Danish
