As a first action I would try connecting a 3.3V serial port to see what's going on -- that's also quite easy to do, all you need is a USB-to-serial adapter on 3.3V level (e.g. CP210x, FT232L, PL2303, CH341, ...) and a recycled CDROM audio cable (find it in the electronics bin of your choice) with JST 4-pin 2.0mm pitch connector (the RT2300/EA8450 got a 6-pin JST, but 4-pin will fit and is sufficient, and much easier to find).
In case the serial console stays blank (or shows breakage before reaching U-Boot) you will have to fetch the bigger gun and wire up JTAG. This is a bit harder as it requires soldering 7 wires to tiny unpopulated 2.0mm pads and connecting it to an OpenOCD-compatible JTAG adapter (e.g. anything with FTDI FT2232H chip).