TM8100 Mobile Radio Service Manual Servicing of Control Head 159
May 2004 © Tait Electronics Limited
Tas k 3 —
All LEDs Faulty
If the display functions correctly but all the LEDs are faulty, repair the
control head as follows:
1. Disconnect the control-head loom.
2. Replace IC3 [at 1D5] which drives the switching transistors for
the LEDs. See Figure 7.3.
3. Reconnect the loom and test the user interface. If the fault has
been removed, return to Subsection 5.2 (on page 109). If it has
not, the repair failed; replace the control-head board as described
in Subsection 7.4 (on page 163).
Tas k 4 —
Display and All LEDs
Faulty
If the display is faulty as well as all the LEDs, repair the control head as
follows:
1. Use a multimeter to measure the 3.3 V DC supply voltage across
C1 [at 1D2] (see Figure 7.2). If it is correct, go to Step 3. If it is
not, go to Step 2.
2. Check for shorts to ground of the 3.3 V supply. Repair any fault
and go to Step 8.
3. Use the multimeter to check that the
RST line at pin 6 [at 1E10] of
IC7 is high. The level should be 3.3 V. If it is, go to Step 5. If it
is not, go to Step 4.
4. Check for continuity in the LCD driver circuitry (D22, C12,
R27) [at 1E9 and 1E10] (see Figure 7.2). Repair any fault and go
to Step 8. If there is no continuity fault, replace IC7 and go to
Step 8.
5. Use the multimeter to check that the
OE line at pin 8 [at 1F10] of
IC5 is low. The level should be less than 0.6 V. If it is, replace IC7
and go to Step 8. If it is not, go to Step 6.
6. Check that the voltage at pins 4, 10 and 14 of IC5 is 3.3 V DC.
Also check that pin 7 [at 1J8] of IC5 is at ground. If the voltages
are correct, replace IC7 and go to Step 8. If they are not, go to
Step 7.
7. Check for continuity between IC5 and the control-head
connector SK1. Also check for shorts to ground between IC5 and
SK1. Repair any fault and go to Step 8.
8. Confirm the removal of the fault, and return to Subsection 5.2. If
the repair failed or no fault could be found, replace the control-
head board as described in Subsection 7.4.
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