Ericsson PF 768 Troubleshooting Instructions page 40

PF768, Standard Electrical Repairs
Measure the voltage at the unmarked side of the R630-R634 resistors (~3.2V).
• If the voltage is too low at one or more of the resistor, measure the resistance of
the corresponding resistor (all are of class A and ~100 kohms).
* If all the resistances are correct, check the solderings at D600 1, 120 and
122-128.
* If the solderings are correct, replace D600 (class B, fig. 7.3).
• If the voltages at both sides of all the resistors are correct, but the keyboard isn't
functional, check the solderings at D600 pin 1, 120 and 122-128.
* If the solderings are correct, replace D600 (class B, fig. 7.3).
* If it doesn't help replacing D600 remove the dome switches again.
Check if there's VDIG (~3.2V) voltage at the marked sides of all the key-
pads in the row that isn't functional (fig. 7.6). Note that there's VBATT
(~4.8V) voltage at the marked side of the "No" keypad.
* If VBATT voltage is missing at the "No" keypad there's a foil dam-
age and the phone is to be discarded.
* If the VDIG voltage is missing at a part of a row (as described in fig.
7.4) there's a foil damage and the phone is to be discarded. This can
easily be verified by measuring the resistance from the marked side of
a functional keypad to the marked side of a non-functional keypad (~0
4/00021-2/FEA 209 544/11.C
Fig. 7.6
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