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Troubleshooting the Controller/Display
Keyboard
If the pull-up voltages are present at the end of the ribbon cable and the voltages are not
pulled down when a key is pressed, the problem is most likely on the A1 Keyboard
assembly. If the pull up voltages are present and are pulled down when a key is pressed but
the controller does not respond, the problem is most likely at the A7 Controller assembly.
The knob can be checked with an oscilloscope at the J4 connector on the A7 Controller.
When the knob is turned, pulses should be present on A7-J4 pins 19 and 21. When the
knob is pushed the level at A7-J4 pin 23 should change states. The A1 Keyboard end of
the ribbon cable should also be checked for +5 V on pins 15 and 16. If the signals are
getting to the A7 Controller the problem is most likely at the A7 Controller assembly.
Where to Go Next
If either the A1 Keyboard or A7 Controller assemblies measured in-correctly, go to
chapters 8 and 9.