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Thread: Need help with 11/23 system

  1. #11


    The BDV11 terminators is soldered into place while the backplane one are in sockets. You probably need to remove the backplane to get the terminating resistors out of their sockets. I had to do exactly this a year ago when building a PDP-11 from an old ex uVAXII BA23 chassi.

    While checking the BDV11 you could also check if the 22 bit ECO has been applied. There should be connection between BC1 .. BF1 and the E1 terminating resistor pins 12..15. Probably not a show stopper, though.

    BTW. Today I fiddled with a BDV11. It turned out that the toggle switches on the BDV11 didn't made contact very well which made the system remain in HALT very often, even though the switch was in the right position. The switch is going to a pair of inverters forming a SR flip flop and sometimes they were stuck in HALT enable...

  2. #12


    Looked at what was involved in getting to the terminating resistors from the backplane. Wow, that is a hassle!! I did get PDP11gui running and even with other boards in place it continued to run when I was examining I/O which takes a long time to run. So still don't know what is the culprit for the sporadic behavior during normal startup. I do want to run a TU58 emulation so I have to get another cable for the DLV11J so that will be several days. The BDV11 does not have the 22 bit ECO applied.



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