Good ay all,
So I have the same problem on my Atari 400 the Shift, Cntrl, and Break appear not to work. This thread has been a wealth of information. I have checked all the connections, reflowed the solder and checked continuity, all seems to be okay. When I look at the signal on the Pokey pin 16 (KR2) it changes state from 5V to around 4.5V when the shift key is pressed. Is this enough of a drop to trigger the Pokey chip?