I was called to repair a TV last night by a friend of a friend. He mentioned that the TV in his workshop had been broken for a few days, and he missed some important football matches. He asked me to help, and I couldn't refuse. To be honest, the Germany vs. Argentina match was my favorite, and I really didn’t want to miss it. But when someone needs help, you have to step up, even if it means sacrificing your own entertainment.
So I went to his workshop, which is an aluminum alloy factory. In what they call the office, there was a Panasonic 25V42G lying quietly, as if silently recalling its past glory. It probably won’t be used much longer, now that LED TVs are more popular.
After disassembling the set, I tested the CRT tube first, and it was already dead. I thought maybe the problem was with the power supply or the capacitors. I checked the reverse diode capacitor, the correction circuit, and the crystal oscillator, but everything seemed normal. Then I noticed that the protection circuit had been removed. That’s why the tube kept burning. I restored the protection circuit, disconnected the high-voltage line, and confirmed that +B voltage was stable at 145V—no power issues.
Next, I measured the line current, and it was over 800mA, which triggered the protection. So the problem must be in the high-voltage package. Upon closer inspection, I found signs of breakdown near the focus and acceleration poles. The package had burned into a carbon shape, clearly damaged.
The high-voltage package was almost out of stock, but the apprentice had an old one from another machine. Within 30 minutes, we had a replacement. I installed it, turned on the TV, and the line current dropped to 320mA. The filament was bright, and I thought it was fixed. But the screen stayed black. No image, no picture—just a blank screen. I tried adjusting the accelerating voltage, but nothing changed.
I checked the RGB output from the deflection board, and each was around 160V, so the output circuit was working. Then I tested the ABL resistor R522 (22K), and it was fine. This was strange. If the luminance signal was faulty, the screen should have responded to brightness adjustments. So the issue had to be with the high-voltage package itself.
The apprentice said the TV had been in good condition when he bought it, and the high-voltage package was supposedly okay. But after checking, I found that the focus line had a resistance of less than 3K to ground. When I unplugged the focus and acceleration leads, the resistance became infinite. That meant the focus pin was shorted to ground.
Inside the tube socket, I saw black carbon buildup between the focus and grounding pins. That explained the black screen and no image. After replacing the tube socket, everything worked perfectly.
When I asked the user if the screen was blurry every time he turned off the TV before it broke, he said yes. At first, it took a few minutes for the image to clear, but later it took nearly an hour. He thought the problem was just a minor glitch, but it ended up causing serious damage. I shook my head and told him that people often ignore small issues until they become big problems.
As I packed up, the Germany vs. Argentina game was about to start. I laughed and said, "You guys will have to watch the game together!" He promised to call me if anything else went wrong.
For beginners, remember: when dealing with a color TV that has no picture, always check the CRT first. Also, make sure the +B voltage is stable, and test the reverse diode capacitor and the correction circuit. If the TV uses a crystal oscillator, check for leakage and ensure proper excitation. Otherwise, you might burn the tube again. And always be cautious when testing line current—any slight anomaly should prompt you to disconnect immediately to protect the tube.
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