February 2012 23 – 375
Measure
key matrix
An almost complete statement about the condition of the keys can be made by way of ohmic
measurement of the key matrix.
8 Shut down the control and switch off the machine.
8 Remove the keyboard from the console.
8 Place the front panel of the keyboard on a soft surface.
8 Leave the ribbon cable to the screen soft keys connected.
8 Set a multimeter to "alarm" (acoustic signal) or to ohmic measurement.
8 Hold the needle tips to the pins of the key to be examined.
--> See figure "Terminal strip X57 for the key matrix“.
Use the key matrix with the pin layout.
--> See ”Key matrix of the keyboard units” on page 23 – 382;
--> See ”Key matrix of the screen soft keys” on page 23 – 392.
8 Press the key to be examined. If the key functions, the multimeter will "ring". If you use ohmic
measurement, the measured resistance is approx. 1 ohm (consider the resistances of the measuring
lines and the test adapter).
Terminal strip X57
for the key matrix
Figure: Terminal strip X57 for the key matrix (lower row: pins 1a to 25a; upper row: pins 1b to 25b)
Observe the ESD precautions. --> See ”Important information” on page 29 – 515.
Limitation:
The alarm method cannot be used to test the cross points of the scan lines (SL) and the
return line 0 (RL 0).
There are logical gates between RL 0 and the related keys. These gates serve for keyboard
identification of TE 6xx.
Direct ohmic measurement is thus not possible here.
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