[johnnym]

A common fault that these boards do have is the failure of a tantalum capacitor in the PS/2 keyboard circuit. In the case of my board, the cap was factory placed with the wrong polarity. (Later revisions of the board had the cap placed the other way around, so when I replaced it I orientated it in that way.

Didn't know that, thanks Irinikus, I'll check that on mine when I find the time.

[...]
I think there's a problem during the power up routine because of the led...

I have a lot of this mothers and I need some of them...so I'll be working hard on it.

Just to be sure:

• Are you using an original PSU to power the MLBs? Are all voltages (you wrote "tension" earlier but surely meant "voltages", which is interesting, because in Germany we have the same word for tension and voltage, which is "Spannung", is it similar in Argentina?) correct and match the numbers giving in the manual on page 114?
  
• Does any of the bigger chipset chips get really hot during operation (maybe use an infrared thermometer)?
  

Then:

1. Do you get anything on the serial console (w/o keyboard attached)?
   
   
2. How many memory modules do you have installed? It needs at least 4 of them because it has a 128 bits of data + 4 bits of parity memory bus width. And what happens if you start w/o memory modules installed, any beeps then?
   
   
3. Does it make a difference if the riser card is installed? I have a 255 4/300 myself (in storage at a remote location), but can't remember if the riser is passive or has any active components, I believe the older 200s had an active riser with Digital PCI bridge and Intel southbridge on it and wonder if they would POST at all w/o them installed. But from your pictures it looks like these chips are on the MLB, so the riser could be passive. But still, it could make a difference when it is installed, so give it a try.
   
   
4. Have you tried a different setting for the CPU speed? Maybe try at slowest setting 6, 7, 8 all ON (see page 118 in the manual (Digital AlphaStation 255 Family User Information, EK-VLLXA-UI. B01)).
   
   
5. You could also give it a try to start w/o the battery inserted or the plus side insulated. That should produce a NVRAM/TOYclock "error".