Service | Model 8904A |
A2 DIGITAL ASSEMBLY TO A1 KEYBOARD ASSEMBLY INTERFACE
Description
The following procedure will help identify whether a keyboard failure is due to the keyboard itself or the controller. It does this by checking signals on the interface between the two assemblies.
If the tests pass but the instrument does not respond to keyboard inputs, the A2 Digital Assembly should be replaced. If the tests fail, trace the signal to the A1 Keyboard Assembly. Retest the line that was faulty to determine whether the fault is in A2 or its interconnection to Al . Refer to Table
Equipment
Oscilloscope .......... ... . ....................................... HP 1740A or Tektronix 2235
Procedure
la. Quick Key Check
NOTE
This check will quickly verify that the keys operate properly. If this check fails, run the following check to pinpoint the failure.
a.Check that switches 1and 2 of the Service Switch, S1, on the A2 Digital Assembly are open and switches 3 through 10 are closed.
b.On the Multifunction Synthesizer, press SHIFT PRESET. After the instrument presets, key in
SHIFT SERVICE
fl (Keyboard Check)
c.Press each key and check that the name of the key which appears in the lower, left hand of the display agrees with the key pressed.
NOTE
Abeep will also be heard after each keypress. Press f4 twice to exit this mode.
1b. Key Check
a.Check that switches 1 and 2 of the Service Switch, S1, on the A2 Digital Assembly are open and switches 3 through 10 are closed.
b.On the Multifunction Synthesizer,press SHIFT PRESET. If the instrument does not preset, switch LINE to OFF and then to ON. If the instrument does not preset, the A2 Digital Assembly or A4 Power Supply is probably faulty.
c.After the instrument presets, connect a dc coupled,
