TM8100 Mobile Radio Service Manual Diagnosis of Faults on Main Board 195
May 2004 © Tait Electronics Limited
4. The VCXO tank circuit (Q501, D501, D502, XL501 and
associated components) or the crystal XL501 [at 5D3/5E4] is
faulty (see Figure 9.12). If not already done, remove the main-
board assembly from the chassis, and remove the
VCXO BOT can.
Locate and repair the fault, confirm the removal of the fault, and go
to Step 9. If the repair failed, return to Subsection 8.1 and replace
the complete main-board assembly.
5. There is a fault in the CODEC 2 circuitry or with the digital
signals to and from IC205 [at 2P2/2D12]. The CODEC 2
circuitry comprises IC205 and associated components under the
CDC TOP can (see Figure 9.16 in Subsection 9.5) as well as R246 [at
2Q1/2C13] under the
CDC BOT can (see Figure 9.3 of
Subsection 9.1). If not already done, remove the
CDC TOP can.
6. Check the signals
DIG CDC2 LRCK at pin 10 of IC205, DIG CDC2 SCLK
at pin 12,
CDC2 DIG SDTO at pin 8, and DIG CDC2 SDTI at pin 9 [at
2Q2]. The signals should be active 3.3 V digital signals to and
from the digital board. If the signals are correct, go to Step 8. If
they are not, go to Step 7.
7. If any or all digital signals are missing, check the connections
between IC205 and the digital board. Repair any faults such as
open circuits, and return to Step 1. If the connections are not
faulty, then the digital board is faulty. Return to Subsection 8.1
and replace the complete main-board assembly.
8. The CODEC 2 circuitry identified in Step 5 is faulty. Locate and
repair the fault, confirm the removal of the fault, and go to Step
9. Note that, if the circuitry is functioning properly, probing the
TP501 test point [at 5F5/5G5] (see Figure 9.11) during power-up
will show a five-step staircase signal followed by a random nine-
step staircase signal — this is the expected power-up auto-
calibration sequence. If the repair failed, return to Subsection 8.1
and replace the complete main-board assembly.
9. Replace all cans. Repeat Steps 1 to 3 to confirm the removal of
the fault. If the repair failed, return to Subsection 8.1 and replace
the complete main-board assembly.
To Next Page
Loading...
