I have been tasked with trying to repair 2 CPU boards which have similar faults. Both will not boot correctly / successfully. The LED display sometimes shows just 2 dots, or a numeral '0', and if left for a while, on occasion has progressed to '3'.
Does anyone have some more technical info or advice on the CPU boards, specifically the bootup procedure / checking performed. I have gathered that once it reaches step 4, a RAM check is made, but I have no details on what is required for the earlier steps.

So far, I have checked the main supply voltage, 5V which appears stable at 5.1V under load. Checked the 12V lines too.

Replaced the ECL clock generator modules, replaced the DS12887 real time clock module, replaced tantalum capacitors on the board, resoldered PLCC socket etc etc.

I can see no physical reason for the boards not to work, and there is no obvious damage evident or smells.

At the moment, I have no further leads to pursue as tech info is limited.

My current hypothesis is a hardware inhibit such as a low voltage or missing clock is preventing the cards booting further, or age-related degradation of flash memory in the bios is the cause.

The first card failed unexpectedly while in service, and the second card was fitted as a spare replacement. The second card also failed after approximately 6 hours in service during the night.

Some pics of the card here:




Thanks in advance...