CRT TV Power Supply Issues: Troubleshooting & Fixes

🔹 Introduction

CRT TV Power Supply Issues (Cathode Ray Tube) TVs have a primary power supply section that converts AC to DC and provides necessary voltages for different circuits. Over time, power failures are common due to component aging, voltage fluctuations, and faulty parts.

This guide covers common CRT TV power supply issues across all major brands, including Sony, Samsung, LG, Philips, Panasonic, Toshiba, Sharp, and Chinese models.

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Fixing CRT TV Power Supply Issues

🔹 Understanding CRT TV Power Supply Issues

Before troubleshooting, let's understand how the CRT TV power supply works and its key components.

🔴 Common CRT TV Power Supply Issues & Fixes

🔹 No Power – CRT TV Power Supply Failure

🔸 No LED, no display, no sound.

🔹 CRT TV Power Supply Clicking Sound Issue

🔸 Repeated relay clicking, but no startup.

🔹 Standby Mode – CRT TV Power Supply Not Turning On

🔸 Standby LED is ON, but the TV won’t start.

🔹 CRT TV Power Supply Low or Fluctuating Voltage

🔸 Screen dimming or sudden shutdowns.

🛠️ Advanced CRT TV Power Supply Troubleshooting

✔️ How to check B+ voltage and diagnose failures.

⚡ Section 1: Understanding the Primary Power Supply in CRT TVs

Before troubleshooting, let's understand how the primary power supply works in a CRT TV.

🔸 Key Components of the Power Supply:

✅ AC Input Circuit – Includes power cord, fuse, and EMI filter.
✅ Rectifier Circuit – Converts AC to DC using a bridge rectifier and filter capacitors.
✅ Switching Regulator (SMPS IC) – Provides regulated B+ voltage (90V-130V).
✅ Chopper Transformer – Steps down high-voltage DC for different circuits.
✅ Secondary Output Section – Distributes power to horizontal deflection, vertical deflection, and audio circuits.

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🔍 Section 2: CRT TV Power Supply Common Issues & Fixes

🔴 1. No Power – TV Completely Dead

🔹 Symptoms:

🔸 No LED indicator, no relay clicking sound, no display or audio.

🔹 Possible Causes & Fixes:

🔹 Blown Main Fuse – Check with a multimeter. Replace if blown but check for short circuits before replacing.
🔹 Faulty Power Cord or Switch – Inspect and replace if needed.
🔹 Bridge Rectifier Failure – If any diode in the rectifier is shorted, replace the full set.
🔹 Open Startup Resistors – Check high-wattage resistors (100KΩ - 1MΩ) in the SMPS circuit.
🔹 Shorted HOT (Horizontal Output Transistor) – A shorted HOT will prevent the power supply from working.

🛠️ Quick Fix:

1️⃣ Disconnect the B+ output to the horizontal section and check if the power supply turns ON.
2️⃣ If yes, replace the HOT transistor and check the flyback transformer.

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🔴 2. Standby Mode But Won't Turn On

🔹 Symptoms:

🔸 Standby LED glows, but the TV does not power up.

🔹 Possible Causes & Fixes:

🔹 Defective Standby Transformer – If the standby transformer has no secondary output, replace it.
🔹 EEPROM Corruption – Some CRT TVs have EEPROM issues causing boot failures. Try resetting it.
🔹 Dry Solder Joints in Power Circuit – Inspect and resolder cracked joints.
🔹 Faulty Remote Sensor or Power Button – If the TV works with manual buttons but not the remote, replace the IR sensor.

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🔴 3. Clicking Sound (Relay or Ticking Noise)

🔹 Symptoms:

🔸 Repeated relay clicking, but the TV doesn’t turn on.

🔹 Possible Causes & Fixes:

🔹 Shorted HOT (Horizontal Output Transistor) – A very common issue. Check and replace HOT.
🔹 Faulty Flyback Transformer – If B+ voltage is present but no high voltage, the flyback may be faulty.
🔹 Overloaded SMPS – Unplug the secondary loads and test the SMPS separately.

🛠️ How to Check HOT (Horizontal Output Transistor)?

1️⃣ Set the multimeter to Diode Mode.
2️⃣ Measure between Collector-Emitter. If shorted (0V), replace HOT.

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🔴 4. Low or Fluctuating Voltage Output

🔹 Symptoms:

🔸 CRT TV turns ON but has low brightness, distorted picture, or sudden shutdowns.

🔹 Possible Causes & Fixes:

🔹 Weak Electrolytic Capacitors – Bulged or leaking capacitors cause voltage instability. Replace them.
🔹 Defective Voltage Regulator IC – Measure the output voltage and replace if unstable.
🔹 Overheated Components – A faulty flyback transformer or HOT can cause overheating.

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🛠️ Section 3: Advanced Troubleshooting Techniques

🔸 How to Check Power Supply Output?

✔️ Use a multimeter to check the B+ voltage. It should be between 90V - 130V DC.
✔️ If the voltage drops under load, suspect dry capacitors or a weak transformer.

🔸 How to Isolate Power Supply Issues?

✔️ Step 1: Disconnect B+ line and check if the power supply works.
✔️ Step 2: If it works, check the horizontal deflection circuit for shorts.
✔️ Step 3: If it doesn’t work, test the SMPS switching IC and chopper transformer.

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📚 Other Lessons Links

🔗 How to Test a CRT TV Flyback Transformer
🔗 Troubleshooting Horizontal Deflection Issues
🔗 CRT TV Vertical Deflection Problems & Fixes

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🌐 External Reference (Wikipedia)

For more details on Switching Power Supplies, visit Wikipedia – Power Supply.