Ericsson GF 768 Troubleshooting Manual page 41

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• If the resistance is too low, replace Z200 (class B, fig. 8.3). The resistance usually becomes a few ohms when
Z200 breaks.
Give the board power and start it up by pressing the On/Off key (in the fixture or in the back cover with a dummy
battery inserted, mount system connector to make the board lie steady in the back cover).
Measure VRAD at C458 (fig. 8.3, ~3.8V).
• If VRAD is too low, usually ~3V, replace N453 (class A, fig. 8.3).
If the fault remains, send the phone to the next level.
8.3 Connect a call at powerlevel 5 and –68.5dBm signal strength.
If you can connect a call, go to 8.4.
If you can't connect a call, open the phone and check for water damage.
Make sure the back cover is of the correct model since there is two kinds. Fig. 8.1 shows what kind of back cover
is to be used with which board.
Replace the antenna connector (if it hasn't been replaced yet) and try again. Note that there are different models of
the connector. It's important that you don't assemble the wrong one. Fig. 8.2 shows the different kinds of connec-
tors and which boards they belong to.
• If you were able to connect a call, go to 8.4.
The fault is probably Tx-related or there's a feed voltage fault if you still can't connect a call.
Give the board power and start it up by pressing the On/Off key (in the fixture or in the back cover with a dummy
battery inserted, mount system connector to make the board lie steady in the back cover).
Measure VRAD at C458 (fig. 8.3, ~3.8V).
• If VRAD is too low, usually ~3V, replace N453 (class A, fig. 8.3).
If the fault remains, send the phone to the next level.
Fig. 8.3
Troubleshooting guide
41