Repairing a CRT TV is almost complete, but the high-voltage package is a component that often wears out. It's not uncommon to find yourself without the right parts, which can be frustrating. However, giving up isn't always the best option. With some courage and careful thinking, you can still get your old TV working again. Even though it might not look exactly like it did before, there's something special about bringing it back to life.
The high-voltage package, also known as the line output transformer, plays a key role in CRT TVs. Its main function is to generate the anode high voltage and provide focus, acceleration, and G1 voltages. It’s important to note that the deflection current doesn’t come from the high-voltage package itself, but from the S-correction capacitor. When the line tube turns off, the B+ voltage charges the S capacitor through the high-voltage package and the deflection coil. This process involves passing current through the high-voltage package, making it a critical component in the system.
Due to its operation under high temperature, high frequency, high voltage, and large current conditions, along with exposure to moisture or dust, the high-voltage package is prone to failure. Common issues include breakdown of internal capacitors, short circuits between windings, leakage or breakdown of the high-voltage silicon stack, aging components, and reduced insulation performance leading to internal or external arcing.
Understanding the key terms related to the high-voltage package is essential for proper diagnosis and repair:
- HV (Anode High Voltage): Typically ranges from 23KV to 29KV depending on the picture tube size.
- FV (Focus Voltage): Usually obtained via a resistor potentiometer at the HV terminal, ranging from 3KV to 10KV.
- SV (Acceleration Pole Voltage): Also derived from the HV terminal, usually between 150V and 1000V.
- AFC (Automatic Frequency Control): Refers to the synchronization signal used by the scan chip and CPU.
- ABL (Automatic Brightness Control): Monitors the HV current to regulate brightness.
- Primary and Secondary Windings: The primary has fewer turns and is less likely to fail, while the secondary has many small turns and is more prone to short circuits.
- Inductance: The opposition to changes in current in a coil, measured in millihenrys (mH).
- Forward/Reverse: Refers to the direction of current flow during scanning cycles.
- Rectification: The process of converting AC to DC, with forward and reverse rectification producing different voltage levels.
- Polarity of Winding: Critical when rewinding or replacing the package; incorrect polarity can lead to improper voltages.
- Field Power Supply & AFC Adjustments: Can be adjusted using self-wound coils if original parts are unavailable.
- Circuit Board Traces: Sometimes need to be cut and reconnected carefully to ensure correct functionality after repairs.
When working with high-voltage components, always use appropriate tools like a 100K ohm range multimeter or megohmmeter to check for shorts or leaks. Be cautious—high voltages can be dangerous if mishandled. If you're unsure, it's better to consult a professional or refer to detailed schematics.
Below are some common high-voltage package data sheets for reference:
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