I don’t think any external hardware could prevent booting. The problem is, as @Bjoern pointed out the mainboard and the display have separate code and the versions have to match.
Measure your power supply output.
You could load up Prointerface and try to connect via USB. There is a USB to serial chip on the mainboard. Most of them use generic drivers but if your PC won’t show a com port when you plug in the usb cable don’t bother trying to establish a serial connection.
My strong suspicion is your mainboard is toast. There was another thread not too long ago where someone found a source for a new (old stock) SV04 mainboards.
There is (as far as I know) no drop in replacement for your mainboard. There are boards with enough drivers for an IDEX setup but none I’ve seen support 3 heaters out of the box.
The other consideration is the ribbon umbilical cables that plug into the SV04 mainboard. To use a generic board you’ll have to cut the connectors and identify all the wires or build an umbilical from scratch.
Quick and dirty - disable one extruder and use a generic 4/5 driver board. I seem to recall someone (in this forum) was plugging Creality Sprite umbilicals into the SV04 board so I would assume there is a matching mainboard… Don’t know which model it is. It would be possible to sync up 2 boards under Klipper and get back to IDEX.
The other option is put a mcu board on each extruder and use a low cost 4 driver mainboard. You’d need a host computer to run Klipper to talk to the 3 MCU’s. The good part is the umbilical reduces to 4 wires per toolhead.