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circuit protektor sharp 20r200 with ix3098

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Understanding Sharp 20R200 Protection System

Sharp 20R200 with IC program IX3098 and Chroma M52340 is an older model, but it still frequently comes into repair workshops.

Entering Service Mode & Protector Bypass

  • Service Mode Switch (S1006): This model uses a hardware switch (S1006) located on the main PCB near the tuner, linked to pin-37 of the IC program. To enter service mode, flip the switch to the "SERVICE" position (which shorts pin-37 to ground).
  • Protector Input Pin: The protection circuit has its input at pin-38 of the IC program, where normal condition voltage is "zero". To paralyze the protector, pin-38 can be shorted directly to ground.
  • The circuit protector is directly related to the heater voltage from the flyback transformer.

Three Conditions That Trigger Protection

There are three main conditions that can cause the protection circuit to activate:

1. X-Ray / High Voltage Protection

Activates if flyback voltage exceeds normal levels. If flyback voltage rises, heater voltage also increases, causing Zener diode D610 to break down and push the protection pin voltage to "HIGH".

2. Low Heater Voltage / Lost Voltage Protection

Activates if heater voltage drops or is lost due to a broken flyback, horizontal circuit issues, or a shorted deflection yoke. When heater voltage drops or is lost, transistor collector Q603 goes to a "HIGH" voltage state (normal collector voltage is "zero").

3. Memory IC Issues

Data corruption or memory IC failure (this matter still serves as a question mark in certain cases).

Practical Repair Experiences

Experience 1: VCC Voltage Drop

  • A technician friend encountered a stubborn protection problem on this model. The protection circuit was inspected and found normal, and the memory IC was replaced.
  • Root Cause: The VCC voltage of the IC program dropped slightly due to a partially shorted (leaky) bypass capacitor on the 5V VCC line.

Experience 2: Crystal Oscillator Fault

  • When turning the TV on, the green indicator light turns on for a moment, then turns red and blinks. Trying again yields the same result.
  • Even with the circuit protector paralyzed, the issue persisted. Surprisingly, when switch S1006 was set to the "SERVICE" position, the TV turned on normally with a green indicator, but returning it to normal made the red LED blink again.
  • Root Cause: After hours of troubleshooting over 2 days, the problem was finally solved by re-soldering the crystal oscillator on the IC program.

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