TM8100 Mobile Radio Service Manual Diagnosis of Faults on Main Board 209
May 2004 © Tait Electronics Limited
Tas k 1 —
Check Power Supply
First check the power supplies for the transmitter circuitry.
1. Set the DC power supply to 13.8 V, with a current limit of 9 A.
2. Enter the CCTM command 326 5 to set the radio to maximum
power.
3. Enter the CCTM command 33 to place the radio in transmit
mode.
4. Check for more than 13 V DC at the drain of Q306 [at 3C3/3E3]
by measuring the voltage at the point on L306 [at 3D5/3F3]
shown in Figure 9.20 and Figure 9.21. Also check for more than
13 V at the common drain of Q309 [at 3F3/3E5] and Q310 [at
3F2/3D5] by measuring the voltage at the point on L310 [at
3F5/3F5] shown in Figure 9.18 and Figure 9.19. Use a needle
probe or else remove the
PAF TOP and PAD TOP cans. If the supply
is correct, go to Step 5. If it is not, go to Subsection 9.1 on the
power-supply circuitry.
5. Check for 9.0 ± 0.5 V DC between the 9
V0_TX and GND test points
[at 3A9/3J1] (see Figure 9.17). If the supply is correct, go to Task
2. If it is not, go to Subsection 9.1.
Tas k 2 —
Check Forward and
Reverse Powers
Next check the forward and reverse power for an indication of which
part of the circuitry is suspect.
1. Enter the CCTM command 318 to check the forward power.
The value returned is the voltage in millivolts corresponding to
the power level, and should be as shown in Table 9.6.
2. Confirm the above result by checking the level at the
FWD PWR test
point (see Figure 9.17) using an oscilloscope.
3. Enter the CCTM command 319 to check the reverse power. The
values returned is the voltage in millivolts corresponding to the
power level, and should be as shown in Table 9.6.
4. Confirm the above result by checking the level at the
REV PWR test
point (see Figure 9.17) using an oscilloscope. If the oscilloscope
momentarily indicates a very high reverse power, then the most
likely scenario is that the antenna VSWR threshold has been
exceeded and the PA has shut down to very low power. Check
the 50 W antenna load.
5. If the reverse power is momentarily too high, the directional
coupler, PIN switch or LPF is suspect; go to Task 11. Otherwise
go to Task 3.
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