Troubleshooting

1
Troubleshooting

• Some methods of isolating defects
• Visual observations with power off.
• Cautious physical touching of components for
  temperature.
• Voltage checks.
• Signal tracing
• Signal injection.
• Resistance testing.
• Component testing.

2
Troubleshooting

• Some test equipment used
• Oscilloscope
• DMM
• Appropriate I.F., R.F., and video signal
  sources.(Ex. NTSC signal generator)
• Curve tracer
• Variac
• Isolation transformer

3
Troubleshooting and Localizing Faults

• Important practices
• Visual checks with power off.
• Use schematic diagram to identify and locate
  components.
• Clear power supply and PS network.
• Note a horizontal defect can disable vertical
  sweep voltages. Why? (scan derived supply)
• Select appropriate troubleshooting method in
  order to localize the fault.

4
Troubleshooting Deflection Circuits

• Vertical deflection symptoms and causes
• Fuses open, CB or relays open.
• - shorts or heavy leakage from major power
  components such as transistors, diodes, and I.C.s
• No vertical deflection.
• - vertical oscillator or sweep generator
• - vertical driver or outputs
• - loss of B - open yoke

5
Troubleshooting Deflection Circuits

• Vertical deflection symptoms and causes contd.
• Reduced height
• - reduced B ( possible adjustment or bad
  component)
• - transistor leakage
• Poor linearity
• - shorted windings in output coupling
  transformer
• - complimentary symmetry imbalance
• - poor adjustment of height and linearity
  controls
• Ex. Method isolate sync by signal tracing or
  signal injection. If sync is good go to
  driver/outputs.

6
Troubleshooting Deflection Circuits

• Vertical deflection symptoms and causes contd.
• Single white line across CRT.
• - integrator
• What would cause the symptom of a picture with a
  strip across the centre of the screen?

7
Troubleshooting Deflection Circuits

• Horizontal deflection symptoms and causes
• No raster or sound.
• - possible shutdown mode
• - no B
• - no sweep voltages
• - may need to do a manual start up (ch 11)
• No raster sound is normal.
• - a component in the oscillator circuit (or
  B to oscillator if it is not a scan derived
  system)
• - if scan derived check HV d.c. circuit

8
Troubleshooting Deflection Circuits

• Horizontal deflection symptoms and causes contd.
• Narrow raster.
• - low B
• - oscillator sawtooth amplitude is low
• Poor horizontal linearity.
• - sawtooth waveshape is non linear
• - possible transistor leakage or component in
  sawtooth circuit.

9
Troubleshooting Deflection Circuits

• Horizontal deflection symptoms and causes contd.
• Horizontal foldover.
• - too long a sawtooth time constant.
• Non linearity on left side of screen.
• - damper diode (capacitor)
• Picture tearing, horizontal pull, horizontal
  jitter etc.
• - oscillator or AFC components, defective
  I.C.
• Weak or intermittent sync.
• - oscillator freq. Drift, unstable AFC, poor
  reception.