Ericsson PF 768 Troubleshooting Instructions page 38

PF768, Standard Electrical Repairs
Make sure the S820 and S821 (both of class A) switches are intact and correctly sol-
dered.
Measure the resistance of the switch that isn't functional. You measure between pin
1/3 and 2/4 (fig. 7.2). The resistance should be >100 kohms when not pressed and
~0 ohms when pressed.
Fig. 7.2
• If the resistance is high all the time, replace the corresponding switch.
• If the resistance is low all the time, replace the corresponding switch first.
* If that doesn't help, check the solderings at D600 pins 1, 123, 124 and 128.
* If the solderings are correct, replace D600 (class B, fig. 7.3).
• If the switches work as they should, replace the volume keys and try again.
* If that doesn't help, check the solderings at D600 pins 1, 123, 124 and 128.
* If the solderings are correct, replace D600 (class B, fig. 7.3).
7.3 One or more keys of the keyboard aren't
functional.
Open the phone and check for liquid damages.
Remove the dome switches and check for liquid or mechanical damages, especially
around the keys that aren't functional.
Clean the keypads thoroughly. Mount a new dome switches and make sure the key-
board isn't damaged. Assemble the phone and check the function of the keys as in
7.1.
4/00021-2/FEA 209 544/11.C
Fig. 7.3
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