More PDP-11 questions

Hi Toby, the problem in your 11/34 sounds like a non-continuous grant chain. Especially when you remove the terminator at the end, and the system does not hang any longer! Start with a minimal system. So the DD11-PK (first backplane) only contains the 2 CPU boards, the M9312, the console interface board M7859, and the SLU M7856 for the console terminal. Remove the memory module, and put the terminator M9302 in the 9th slot, in positions A-B. Put in *all* other slots that have position C and D free a G7273 card. (I hope you have those, you need 5 of them). (I assume that are the cards you have in your 11/34) With the G7273's you made sure that NPR grant chain is intact. When you power up the /34, RUN should stay off, or pressing CTRL and HALT should make it go off. If you reached this condition, you can remove the G7273 from the slot where you want to install the memory board and install the memory. Test again. Then remove one by one, one G7273 and replace it with a G727A, aka knocklebuster. At a point the RUN LED will no longer go off. That slot has the NPR wire (pin CA1-CB1 connection) cut. That is a slot you can use for a "DMA" device like the RL11 interface. If that slot is not used, you must have an G7273 inserted there, or a G727A *and* re- wire pin CA1 to CB1. In the end, some slots will have G7273's and some will have G727A's. Needless to say, that for preservation of the hardware, switch off the power before swapping even a module that has no components like the G7273. And do not switch the system on within one or two seconds after switching off. A few seconds delay will not hurt! - Henk, PA8PDP.