VII. FAULT FINDING procedure :
Step-1 : Check for any physical damage by opening front panels.
Step-2 : Check the Aux. fuse (300mA) & PT fuse (100mA). If necessary, replace
them. (Do not interchange the fuses). Tighten them properly.
Step-3 : Confirm that the Display PCB's 40 pin connector mate properly with the
Main PCB's 40 pin connector
Step-4 : Connect 'Aux’ supply & PT supply & Switch ON the unit. If the unit does
not get switched ON, then check Power ON switch.
Step-5 : Measure DC voltages on TP5, TP6 & TP4 w.r.t.TP3. They should be
+12V, -12V & +5V respectively. If the voltages are not correct,
remove 40 pin connector and check once again. If the voltages are
correct then there is problem with the Display PCB. Replace the
Display PCB. If the voltages are still not OK, check the mains
transformer. Replace the mains transformer if faulty or else replace
Main PCB.Confirm all DC voltages are OK.
Step-6 : Keep the selector switch to 'N'set position and vary 'N' set control to read
99V to 121V on display. Set 'N set' control to 110V. Keep the selector
switch to 'R' set position and vary 'R' set control to read 104.5V to 109.5V
on display. Set 'R set' control to 108V. Set selector switch to 'L' set
position and vary 'L' set control to read 110.5V to 115.5V on display. Set
'L set' control to 112V. If any of the settings are not obtainable, it means
Display PCB is faulty. Check potentiometers for their open/short
conditions & replace if necessary. If not, IC6 or IC4 or selector switch on
Display PCB may be faulty. Replace the faulty component.
Step-7 : Put selector switch to PT I/P position. Vary the PT/IP and read the
display. If display does not vary then measure AC Voltage at TP4 on
Display PCB w.r.t. GND. It should vary from 0 to 5V AC, when PT/IP is
varied from 0 to 150V AC. If the voltage is not coming, it means that the
sense transformer is faulty. Replace the sense transformer. If the voltage
is OK, check on Main PCB 7.5V DC on TP9 for PT I/P = 110V. If DC
voltage is not OK then IC10 is faulty. If it is OK then either selector
switch on Display PCB is faulty or IC8 on Main PCB is faulty. Replace
the faulty component.
Step-8 : Vary the PT I/P to less than 80V (UV level), then the UV indication
alongwith ‘R’ indication should come. Increase the voltage above
85V then UV command goes “off”. However ‘R’ command remains
“ON”. Increase PT I/P voltage slightly more than 108V, ‘R’ will go
off. This is Bandwidth condition. Increase PT I/P slightly more than
112V, ‘L’ indication should come.
9
To Next Page
Loading...