Some Leds Faulty - Tait TM8100 mobiles Service Manual

Control-Head Board
Faulty
15.2

Some LEDs Faulty

TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
If neither the elastomeric strips nor the LCD are faulty, check the relevant
components on the control-head board:
1. Use an oscilloscope to display the signal at pin 5 of IC5
(see Figure 15.2). The signal should be a square wave with a fre-
quency of about 60Hz and an amplitude that alternates between 0.0
and 3.3V. If the signal is correct, go to
2. Replace IC2 (see
been removed, return to
to Step 3.
3. Use the oscilloscope to display the signal at pin 12 of IC7 (see
Figure 15.2). The signal should be a square wave with a frequency of
about 120Hz and an amplitude that alternates between 0.0 and 3.3V.
If the signal is correct, replace IC5 and go to
replace IC7 and go to
4. Test the user interface. If the fault has been removed, return to
Tasks" on page
control-head board.
If the display functions correctly but one or more (but not all) of the LEDs
D1 to D18 are faulty:
1. Disconnect the control-head loom. Remove the control-head board.
Reconnect the loom to the board.
2. Use a multimeter to measure the forward voltage across each faulty
LED. See Figure
go to Step 3. If it is not, replace the LED and go to
3. If the forward voltage is correct, the LED is functional but the
associated switching transistor is suspect. Replace the transistor
corresponding to the LED in question. The switching transistors
associated with the LEDs D1 to D18 are Q1 to Q4. See
Continue with
4. Test the user interface. If the fault has been removed, re-assemble the
control-head board, and return to
has not, replace the control-head board and return to
on page 155.
Fault Finding of Control Head with 1-, 2- or 3-Digit Display
Figure 15.2). Test the user interface. If the fault has
"Initial Tasks" on page
Step 4.
155. If it has not, the repair failed; replace the
15.1. The voltage should be 2.0±0.4V DC. If it is,
Step 4.
"Initial Tasks" on page
Step 3. If it is not, go to
155. If it has not, go
Step 4. If it is not,
Step 4.
Figure
155. If it
"Initial Tasks"
Step 2.
"Initial
15.2.
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