Williams Johnny Mnemonic
Machine acquired February 2007
Here's a list of problems and solutions found for this machine:
Problem: Display Jailbars
Solution: 6116 RAM chip had bit 7 stuck on.
Problem: Hand switch error.
Solution: There was no hand switch present when I bought the machine, they are no longer available through established channels, and fabricating one proved to have limited success. Since the hand seemed to work well despite the switch not being there, my main goal was to get the "BONG BONG BONG" error report to go away on power up. After several attempts ar getting a switch placed in the hand (that never fit or cleared other mechanism parts, or that actuated reliably with a ball), or a switch actuation that would work based on mechanism movement, I came to the solution here:
So far, this solution seems to work well, and I have not seen any negative effects from not having the standard hand switch.
Problem - After a period of time, the display would only light up the dots on the lower rows, appearing as "garbage". Voltage measurements near the row driver chip across the zener diode would measure very low, and the resistor would get hot, indicating that the chip was locking up.
Solution: At first I thought that the row chip was the problem, but after having no success sourcing a replacement, it hit me one day that you CAN lock up a chip if the control lines are driven with noisy or erratic data. I replaced the data line chip resistors near the data connector (100 ohm and 47K) and the problem went away!