Tait Limited TEL0024 用户手册
T856/857 Fault Finding
C5.3
Copyright TEL
5.1
Visual Checks
Remove the covers from the T856/857 and inspect the PCB for damaged or broken com-
ponents, paying particular attention to the surface mounted devices (SMD's).
ponents, paying particular attention to the surface mounted devices (SMD's).
Check for defective solder joints. If repair or replacement is considered necessary, refer
to Section 3 of Part A.
to Section 3 of Part A.
5.2
Component Checks
If you suspect a transistor is faulty, you can assess its performance by measuring the for-
ward and reverse resistance of the junctions. Unless the device is completely desol-
dered, first make sure that the transistor is not shunted by some circuit resistance. Use a
good quality EVM (e.g. Fluke 75) for taking the measurements (or a 20k ohm/V or bet-
ter multimeter, using only the medium or low resistance ranges).
ward and reverse resistance of the junctions. Unless the device is completely desol-
dered, first make sure that the transistor is not shunted by some circuit resistance. Use a
good quality EVM (e.g. Fluke 75) for taking the measurements (or a 20k ohm/V or bet-
ter multimeter, using only the medium or low resistance ranges).
The collector current drawn by multi-junction transistors is a further guide to their per-
formance.
formance.
If an IC is suspect, the most reliable check is to measure the DC operating voltages. Due
to the catastrophic nature of most IC failures, the pin voltages will usually be markedly
different from the recommended values in the presence of a fault. The recommended
values can be obtained from either the circuit diagram or the component data catalogue.
to the catastrophic nature of most IC failures, the pin voltages will usually be markedly
different from the recommended values in the presence of a fault. The recommended
values can be obtained from either the circuit diagram or the component data catalogue.
5.3
Front Panel LED Indicator
The green "Supply" LED on the T856/857 front panel will flash according to the condi-
tions described in the following table:
tions described in the following table:
Where two or more conditions occur at the same time, the precedence is in the order
shown above (i.e. T856/857 linked has the highest priority, followed by internal error).
shown above (i.e. T856/857 linked has the highest priority, followed by internal error).
Flash Rate
Condition
fast
(
sec. on/ sec. off
approx.)
T856/857 is linked with
PGM800Win
unequal
(
sec. on/1 sec. off
approx.)
microcontroller has detected an
internal communications error -
refer to Section 5.7.1