JUMA TX-500 first power up. No display

[NE5U]

I finally finished the power supply wiring for my TX-500 today. Unfortunately first power up didn't go very well.

Current limited supply set to 14V 1.5A
Press the green power button. No display. If I hold the button in the current comes up to 1.25A then drops to 750mA. When I release the button the power drops (as measured at the two test points) to zero.

There is a jumper on the display board, J1. It's not clear which pins are jumped for MAX232. J4 appears to be a "test" jumper.

Maybe I missed them but documentation seems to be pretty sparse, as in only schematics and a few photos. No firmware has been loaded. Is that the problem (doubt it)?