New file: fixing startup problem on old ADAs.

Hi All,

I had the MP1 open, so I took a shot of a fix that I did to make it
start up reliably.

I spent weeks debugging the issue a couple of years ago, and then I
finally pinpointed
it down to the flaky NMI-signal generating circuit whose purpose is to
cause the Z80
CPU to jump to some safe infinite loop when the power is cut.

Unfortunately, NMI is edge-triggered and the circuit can flake out at
startup,
generating a spike to that input, causing the CPU to enter that same
frozen state
like when power is cut.

I found this myself, and then I learned that they fixed it in later
units
(mine is from 1987).

Here is my fix: cut the trace to the NMI pin (17), and jumper
pin 17 to pin 11 (pulling NMI to +5V).

Annotated image:

http://www.kylheku.com/mp1-files/mp1-repairs/ADA-MP1-kaz-startup-fix.jpg