If you don't have a scope, maybe you could stick a LED between A9 and 3.3v and see it it at least flashes on boot? Espruino should transmit its logo at startup so you should see it flashing if that's the case.
If that works then you can narrow it down to something with the USB TTL dongle... You have connected GND as well as RX and TX?
I did what you said. The LED connected between A9 and 3.3V is not flashing. I made a second board from fresh components just in case I broke something but had the same effect. Looks like the chip is not sending anything to this UART. Maybe there is a pin configuration issue? Maybe because the default package for STM32VLDISCOVERY is LQFP64 and mine is LQFP48 (i changed it in board's config file) there is some pin mismatch? Or some connections on my board make the chip think that it is connected via USB, so it sends nothing to A9, A10 pins?
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