The workstation only post the low level bios (vga bios on black screen), but no srm or arc console ...
I have try to swap the 2 flash eeproms with working one but nothing.
Is there a jumper for NVRAM factory setting like the alphastation 255's jumperblock (JP1 and JP2)?
You could try to use a firmware update disk. This could give you output to the serial console port. I have done this on an AXPpci33 to get it going - IIRC after a similar issue than what you describe - vga bios message on black screen. I needed to set the SROM select jumpers (from the AXPpci33 OEM manual
page 40 (labelled 2-22)) to "Boot from fail-safe floppy loader", insert the firmware update disk and cycle power. Afterwards the machine gave me console output after an endless 48 seconds and allowed to update the firmware.
I assume the AlphaStation 500 could have a similar functionality and you could update the firmware to the original (no real change to your current config, albeit it might work again afterwards) or the latest firmware depending on what you desire.
The AlphaStation 500 manual
also has SROM selection jumpers (see page 120 (labelled C-12)). I assume "Floppy loader" is the relevant configuration.
It could be that I also had to remove the graphics card before using the fail-safe floppy loader to make sure console output goes to the serial console (also make sure that no keyboard is attached!). If it doesn't print anything with the graphics card installed you could retry without it.