Specific Clock Test Points; General Visual Inspection Guidelines - Nokia N900 Service Manual

Specific clock test points

RCLK
Test point J6183 is the RCLK (Reference Clock) input to the device. This is typically 32.768KHz and is driven
from the sleep clock from the base band. When measuring this clock frequency, it may be seen to vary by as
much as +/- 120 ~ 200ppm. The device can only typically tolerate +/- 20ppm in order to maintain transmit
frequency accuracy. To overcome this, the software driver for the device calculates what the actual sleep
clock (RCLK) frequency is and periodically programs the device with this frequency.
The device then internally adjusts its dividers in order to maintain the required output frequency. Using this
method it is possible to reduce the effective ppm of the reference clock down to +/- 14ppm over the full
operating temperature range of -15 to +50 degrees Centigrade.

General visual inspection guidelines

• If the handset has the FMTx antenna in the B-cover then check the condition of the antenna springs and
trace.
• Check that the Si4713 device is placed correctly on the PWB and that there are no obvious signs of damage.
• Check the surrounding components and ensure correct placement on the PWB and that there is no visual
damage. Check that there are no missing components.
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