Ready to Power up the 11/04

Hi Henk, Thanks for the info. I also appreciate the detail on your webpage about the KY11-LB. I think I have got to the bottom of the front panel problem. Initially I thought that it was related to the scanning technique that is used to read the keypad and update the 7 segment displays given the keypad gave the wrong values and sometimes the display was missing segments. After further research it appears not to be the case (which is good). The scanning signals all look good on the scope and the keypad matrix works correctly when tested with a meter. The insight came when I looked at which keys on the number pad worked and which didn't. I came up with the following table Pressed = Displayed 1 = 1 2 = 0 3 = 1 4 = 4 5 = 5 6 = 4 7 = 5 0 = 0 If you convert this to binary it becomes pretty obvious where the problem lies. The invalid display is for the items marked with * and all have the second bit set. If you mask out the second bit you get the displayed value. 0 = 0000 1 = 0001 2 = 0010 * 3 = 0011 * 4 = 0100 5 = 0101 6 = 0110 * 7 = 0111 * The front panel uses a 7447 BCD to 7 Segment decoder to drive the LED modules. If pin 1 (B) on this is not being set when required then the behaviour will be what I am seeing..... it isn't that the keypad is getting it wrong... but the display is showing the wrong value due to a missing bit. Need to do a bit more digging here but given that this line is pulled to +5V via a resistor on the front panel board I am hoping that the problem is either a connection problem on the front panel board with the line not being pulled up or the 7447 needs to be replaced. If there was a break in the ribbon table to the controller board then the bit would always be set and a different set of incorrect values would be displayed. Hopefully there isn't a fault on the controller board that is pulling the pin to ground. Apart from incorrect values, other behaviours of the front panel seem OK. The other display problems with odd segments missing on the 7 segment displays are due to them being socketed (clearly there was some concern about reliability in 1979) with dirty connections. I need to pull each 7 segment display and clean the pins. Pressing on a display that is missing segments will cause them to appear.... might need to solder joins touched up too. So that is all very positive about the front panel. If I can get down to the workshop tonight I will try to validate if it is the 7447 that is at fault. Tony - OK on testing the Grant lines. I will do that. It seems that if the CPU was already halted that a similar BUS Error would result. Apart from checking for address bus activity is there any other way of confirming if the CPU is running or already halted? I am going to recheck the DC LO and AC LO signals on the unibus as well using a scope. The "Hints on testing a dead PDP11" at has a comment that these can cause problems in the BA11-K chassis and cause the processor to halt. Regards Andrew On Sun, Jul 22, 2012 at 9:23 PM, Henk Gooijen <henk.gooijen at hotmail.com> wrote: