Hi Bill, The 11/40 has jumpers on a lot of the basic boards that have to looked at in relation to the optional boards (KE11-E M7238, KE11-F M7239, KT11-D M7236, line clock- M787, and stack limit option. Every option change require changing jumpers. Every memory set has to have the right starting address and parity jumpers. Shorten the bus to cpu and mininal memory, and try a few toggle in programs. If you have a scope, you can scope the unibus. good luck, and feel free to send me ant questions. Paul On Fri, Jun 17, 2011 at 4:53 PM, B Degnan <billdeg at degnanco.com> wrote:

What boards do you have in the system, in particular, what is the terminator at the 'far' end of the Unibus? On machiens with an M9302 terminator (this is common in 11/34 machines, but it can be used in others), a common caus of faults like this is an open grant chain, or a malfunctioning peripharal controller that's asserting a greant to deviced further down the bus when it shouldn't be. The M9302 terminaotr has a circuit that asserts SACK if a grant getrs as far as the terminaotr. The problem comes when that grant doesn't start deassert the grant line becuase it wasn't asserting it in the first palce. The machine thnn totally locks up. Another cause of this sort of problem in soem machines if if the ACLO or DCLO signals on the Unibus are sserted. This might indicate a problem with te appropratie circuitry in the power supply. -tony