Tait TB7100, Service Manual

Page: 288 / 370

290 Transmitter Fault Finding (50W/40W) TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 7 —
Check for Inhibiting
of Transmitter
If the transmitter is drawing no current or the wrong current, check
whether it is being inhibited. This check is also required if a
CO3
error
occurs in Task 1 .
1. If not already done, enter the CCTM command
33
to place the radio
in transmit mode.
2. Check the logic signal at the
TX INH
test point (see Figure 14.6 ).
The signal should be:
3. If the signal is inactive as required, go to Step 4 . If it is active — about
1.1V — the transmitter is being inhibited; go to Step 5 .
4. Enter the CCTM command 32 to place the radio in receive mode,
and go to Task 12 in “Biasing of PA Driver and PAs” on page 297 .
5. Check the logic signal at the
D TX INH
test point ; see Figure 14.18
on page 316 (B1 band) or Figure 14.6 (H5, H7 bands). The signal
should be:
6. If the signal is inactive as required, go to Step 8 . If it is active — about
3.2V — the temperature sensor is suspect; go to Step 7 .
7. Enter the CCTM command 32 to place the radio in receive mode,
and go to Task 8 .
8. The lock status is possibly no longer normal. Enter the CCTM
command
72
and check the lock status.
9. Enter the CCTM command 32 to place the radio in receive mode.
10. The normal lock status is
110
. If it is not, proceed to the relevant
section. If it is, go to Step 11 .
11. Check for short circuits on the
DIG TX INH
line from the
D TX INH
test
point .
12. Repair any fault, confirm the removal of the fault, and go to “Final
Tasks” on page 123 . If the repair failed or no fault could be found,
replace the main-board assembly and go to “Final Tasks” on
page 123 .
TX INH test point: about 0V (inactive)
D TX INH test point: about 0V (inactive)