GH688,GA628, Standard Electrical Repairs
4/00021-2/FEA 209 544/1.G 12 (112)
back cover and run the phone through the test again. This applies espe-
cially for the GA 628.
• If the output power is too low or the Rx-quality value is too high, send the phone
to the next level.
• If the Rx-level value is too high, the phone has to be calibrated and therefore you
have to send the phone to the next level.
• If the Rx-level value is below 40 steps at –68.5dBm signal strength or below 6
steps at –102dBm signal strength, the problem is Rx-related.
Open the phone and check for liquid damage.
Check the antenna connector, X401 (class A, fig. 2.2), and make sure that it isn’t
damaged or dirty (glue, varnish, oxide…) and that the solderings aren’t faulty.
Measure the resistance from C426 (fig. 2.2, measure from the marked side) to
ground (>1 Mohms). The resistance is usually only a few ohms when Z200 (class B,
fig. 2.7) is broken.
Fig. 2.7
Measure the resistance from the anode of V403 (class B, fig. 2.2) to ground (~60
kohms).
• If it’s less (a few kohms), lift one of the V402 pins from the pad and measure
again at the same place.
If it’s correct (~60 kohms), replace V402.
• If the resistance is still too low, replace both diodes.
Measure again after replacing the component(s).
• If the resistance is still too low, measure the resistance of R421 and R422 (both
of class B, 100 kohms, fig. 2.2). Both the resistors are 100 kohms but when you
measure them the instrument will show ~60 kohms.
Check the solderings at C826 (fig. 2.4), Z201, Z500, Z501 and Z502 (fig. 2.3).
Measure the resistance of C540, C541, C542, C543, C544 and C545 (all of them
class B, >200 kohms, fig. 2.3)
If the problem isn’t solved, send the phone to the next level.
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