Problem with DEC LSI11 / KD11-F

Mattis Lind mattislind at
Sat Nov 29 14:22:11 CST 2014

I have been browsing through some of my old Qbus boards and found one
KD11-F (M7264) CPU with 4 k word memory, a couple of KD11-HA (M7270) , a
KDF11-A (M8186) and some assorted memory boards and some SLUs.

All CPUs seemed to work except for the KD11-F board, which was a bit sad
since that was the original LSI-11 board.

I looked at bitsavers for schematics. Indeed there was one, but my board
revision seems to be older. It is not matching layout wise and it has
plenty of patches. Is there a print set for the older revision of the board?

Well, I am not giving up that easy. The clock signal was there so I
attached the logic analyzer over the control chip and was able to find out
the micro address (sampled at falling PH2 clock) and data (sampled at
falling PH1 clock).  The strange thing was that it was not starting at
address 1. It starts of at 89 hex, then steps to 8A and then to 39D. The
data returned is FFFF, FFFF and 708A (forever).
FFFF is supposed by NOP. 708A is also some other valid micro instruction.
(according to the EK-KUV11-TM_LSI11_WCS.pdf

Is the micro code source / dump for the LSI-11 available somewhere?

If I remove one of the MICROMs it starts at 1 and goes on 2,3,4,5,6, etc.
My guess is that one of the MICROMs are bad, forcing some bits low. Or
maybe the strange precharging isn't working?

Now, I have several M7270. I could sacrifice one board to get the other
working. But are the chips identical? The markings on the chips are not

The M7264 board has the following chips:

CP1611B-51  2111549
CP1621B451  23001C201
CP1631B-10   23088A501
CP1631B-07   23087A501

The M7270 board has the following chips:

1611H  21-15579
3007D  23-002B5
3010D   23-001B5
2007C   23-002C4

Is there a engineering drawing printset for the M7270 (KD11-HA) somewhere?


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