Tait TB7100, Service Manual

Page: 139 / 370

TB7100 Service Manual Interface Fault Finding 141
© Tait Electronics Limited October 2005
Task 2 —
Check Input Lines
For an input line suspected or reported to be faulty, proceed as follows:
1. For a suspect
CH ON OFF
line, go to Step 4 . For all other input lines go
to Step 2 .
2. For the suspect line, apply a 3.3 V DC test signal to a connector mated
to the radio connector in question.
3. Check the internal signal for the line under test. If 3.3V DC is
present, go to
Step 7 . If it is not, go to Step 8 .
4. For the
CH ON OFF
line, apply a short to ground on pin 5 of a connector
mated to the control-head connector. Check that there is 3.9 V DC
present on the
ITF ON OFF
line, and that
PSU ON OFF
is approximately
equal to the radio’s primary supply voltage, nominally 13.8 V DC.
5. Remove the short on the connector. Check that, with
CH ON OFF
open-circuit, both
ITF ON OFF
and
ITF PSU ON OFF
are close to 0.0 V.
6. If the voltages given in Step 4 and Step 5 are observed, go to Step 7 .
If they are not, go to Step 8 .
7. The fault lies with the radio’s internal circuitry. If the power-supply
circuitry or the CODEC and audio circuitry is suspect, continue with
the fault diagnosis as in
“Power Supply Fault Finding” on page 127
and “CODEC and Audio Fault Finding” on page 343 , respectively.
If the digital board is suspect, replace the main-board assembly and go
to
“Final Tasks” on page 123 .
8. The fault lies in the filtering, basic processing, or connector for the
line under test. Re-solder components or replace faulty components
as necessary. Confirm the removal of the fault and go to
“Final Tasks”
on page 123 . If the fault could not be found, replace the main-board
assembly and go to “Final Tasks” on page 123 .
Task 3 —
Bi-directional Lines
For a bi-directional line suspected or reported to be faulty, proceed as
described below. In the procedure the direction of the line will need to be
configured. For information on this topic consult the on-line help facility
on the programming application’s
“Programmable I/O”
page.
1. Configure the suspect line as an output, and then carry out the
procedure given in
Task 1 .
2. Configure the suspect line as an input, and then carry out the
procedure given in
Task 2 .