Hi,
As it is stuck during the initialization phace it looks like the software is broken. I know that you can update (or also overwrite to reflash) the firmware on the keyboard by preparing a compact flash card with files you can get from Roland's website. I did that to update my firmware, maybe be executing this procedure you will fix/rewrite the software/firmware on the keyboard. It is at least a test of CPU and the flash rom.
What you could also try boot with just the mainboard (with CPU) and the display (LCD) connected to the jack board (which is providing power) (connection 4 in the wiring diagram on page 14 of the service notes) to see if boots then to see if the other boards are not causing an issue (short/wrong signal etc.).
My reference: I fixed a Elektribe EMX recently, by exchanging mainboard as there was an error on the LCD during the initialization (not blank LCD), the power was provided correctly (common fault is that FUSE1 is blown, which is providing the voltage to the CPU). The only way to fix it was to replace the mainboard with an entire other mainboard from another broken unit (and fix its FUSE1) to get a working unit, so I could only conclude that the software/flash/CPU was broken on the old mainboard. I didn't check any signals or so, just voltages going to the CPU.
Coming back to this it could just as well be that the flash chip with firmware has gone bad... OR that the capacitors C38 & C34 near the power input (next to the warm voltage regulator) have dried up and need to be replaced, make sure that you replace them anyway as they will fail at some point in the future (saw that in a youtube video, the sound would get unstable)
Next to IC13 on the panel-c board what looks like three switches and an indication (Normal vs Debug) could this be the area to hookup a debug console? It says CN14 (Serial and etc) for Connector 14 (CN14) in the wiring diagram. Even on page 32 it says GDB (which seems to be some debugger) next to CN14 and COMP_RXD, COMP_TXD & COMP_CTS & COMP_RTS . I am not sure how to use this. I found the following pointers on
https://ftp.gnu.org/old-gnu/Manuals/gdb/html_node/gdb_125.html The GDB remote serial protocol and
sh-stub.c For Hitachi SH architectures.
What the stub can do for you
The debugging stub for your architecture supplies these three subroutines:
set_debug_traps
This routine arranges for handle_exception to run when your program stops. You must call this subroutine explicitly near the beginning of your program.
handle_exception
This is the central workhorse, but your program never calls it explicitly--the setup code arranges for handle_exception to run when a trap is triggered. handle_exception takes control when your program stops during execution (for example, on a breakpoint), and mediates communications with GDB on the host machine. This is where the communications protocol is implemented; handle_exception acts as the GDB representative on the target machine. It begins by sending summary information on the state of your program, then continues to execute, retrieving and transmitting any information GDB needs, until you execute a GDB command that makes your program resume; at that point, handle_exception returns control to your own code on the target machine.
breakpoint
Use this auxiliary subroutine to make your program contain a breakpoint. Depending on the particular situation, this may be the only way for GDB to get control. For instance, if your target machine has some sort of interrupt button, you won't need to call this; pressing the interrupt button transfers control to handle_exception---in effect, to GDB. On some machines, simply receiving characters on the serial port may also trigger a trap; again, in that situation, you don't need to call breakpoint from your own program--simply running `target remote' from the host GDB session gets control. Call breakpoint if none of these is true, or if you simply want to make certain your program stops at a predetermined point for the start of your debugging session.
Maybe you can catch an exception fault through the serial debugging session?
I hope this input helps you with resolving your issue
