irwin@uiucdcs.UUCP (10/24/84)
The MS780C memory is the 4 meg (256k X 16 boards). You do not say how much you have, and if the two faulty boards are in the last two slots. The memory has to be continuous, so they need to be in the last two slots (not counting terminator) if you disable them. The probable cause of the machine hanging is that the controller is having compound errors. The memory is error correcting type, but if the controller is correcting an error and gets a second error at the same time it gets confused and hangs the buss. This happened on our 780. We were having single bit errors (correctable) so ignored them. When the errors got to confusing the controller, we had to get the bad boards repaired. If you have the 780 on DEC maintenance and if the diagnostic floppies are on site, you can boot the console floppy, enter micro diag #2 and type T on the console, it will test memory and point out the bad boards. When the machine hangs, if you do the ^p and H to get the >>> prompt, you can do a E 20002000/N:2 which is the examine of the memory controller registers at TR1. If you have the docs on the controller and decipher the printout you get on the console, you may determine what the controller is doing. If the above is not enough help, mail me at pur-ee!uiucdcs!irwin.