TB7100 Service Manual Interface Fault Finding 139
© Tait Electronics Limited October 2005
Task 1 —
Check Output Lines
For an output line suspected or reported to be faulty, compare actual and
expected signals as described below. If necessary, determine what an
expected signal should be by copying the faulty radio’s programming file
into a serviceable radio and measuring the relevant points on the latter.
1. Check the electrical signal at the appropriate pin of a connector
mated to the radio connector in question. If the expected connector
signal is not present, go to Step 3. If it is, go to Step 2.
2. If the expected signal is present, there might be no fault on that line
or there could be an intermittent fault. Subject the radio to mild
mechanical shock or vibration, or to a temperature change. This
might expose any intermittent contact, in which case go to Step 3.
3. If the expected signal is not present, check whether the expected
internal signal is present. If it is, go to Step 5. If it is not, go to Step 4.
4. 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.
5. The fault lies in the filtering, basic processing, or connector for the
line under test. Re-solder components or replace damaged or 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.
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