VAX-11/750 EMC Memory Board LEDs

On 7/8/09, Ian King <IanK at vulcan.com> wrote: One possibility is an ECC fault. ISTR that since the boards fire up with zero or random contents, most/all of the locations don't have the right check bits. The board sets the checkbits all at once at power-on, possibly with some sort of startup/refresh counter, so it might take a noticeable time to strobe through the array. Another possibility is that they are a simple access light - I think I've seen those on some 3rd party board - again, at power-on, things aren't stable yet, so you get solid lights until the memory board finishes its own startup. Do the yellow lights seem to vary in brightness under different loading conditions during normal operation or are they essentially dark? Are your RAM chips socketed by chance (probably not - the last socketed memory I remember seeing was Qbus memory for PDP-11s and the uVAX-I). If so, you could pull one chip from one board, forcing an ECC error and watch the behavior. If you have a red LED, too, that might be a hard fault, so the yellow could be soft fault or access. It's been a long time since I've played with 3rd party memory on a VAX, so forgive me if I'm tangling my own memories here. -ethan