I was called by a friend last night, who said that his friend’s TV in the workshop had broken down for a few days, and he missed some important football matches. He asked me to help fix it. To be honest, I was really looking forward to watching Germany vs Argentina—the game of my favorite team. But there was no way around it; I had to go and repair the TV, which meant missing out on some great moments. Still, saving people is always important, even if it means sacrificing a bit of fun.
I arrived at the workshop, an aluminum alloy factory, and found a Panasonic 25V42G lying quietly in the office, 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 TV, I first tested the tube and found it broken. I thought maybe there was something wrong with the reverse capacitor, so I checked the correction circuit, the crystal oscillator, and other components—but everything looked normal. Then I noticed that the protection circuit had been removed, which explained why the tube kept blowing. I restored the protection circuit, disconnected the high-voltage line, and confirmed that +B voltage was stable at 145V.
Next, I checked the line current, which was over 800mA, triggering the protection circuit. After ruling out other possible causes, I focused on the high-voltage package. Upon closer inspection, I saw signs of breakdown near the focus and acceleration poles. Using a scorpion pick, I found it burned into carbon. The market for this kind of high-voltage package is nearly out of stock, but my apprentice had an old machine and sent one over within 30 minutes.
After installing the new part, I turned on the TV. The line current was at 320mA, the filament was bright, and I thought the problem was solved. But the screen remained black—no image, no picture. I adjusted the accelerating voltage, but the screen stayed dark.
I checked the RGB output from the tail end, and they were around 160V, which meant the output circuit was working. Then I measured the ABL resistor R522 (22K), and it was normal. That was strange. If the luminance signal channel was faulty, the screen should have responded when I increased the brightness. So the issue must still be with the high-voltage package.
My apprentice mentioned that when he first got the TV, it showed signs of severe aging, and the high-voltage package was supposedly fine. Based on experience, I suspected a focusing issue. I opened the socket cover and measured the resistance between the focus line and ground—it was less than 3K. When I unplugged the high-voltage package, the resistance became infinite.
Then, the apprentice removed the stem and opened the focus pin. What I saw made me shake my head—there was a lot of black carbon between the focus pin and the grounding pin. That was the problem! The severe leakage caused the focus voltage to short to ground, resulting in a black screen.
After replacing the tube seat, the TV worked perfectly. I asked the user if the image was blurry every time he turned off the TV before it broke. He said yes, and it took longer each time before the image appeared. At first, it was just a few minutes, but later it took almost an hour. He thought the TV would work normally again, but instead, it completely failed.
I shook my head and told him that people often ignore small problems until they become big ones. A simple header failure led to a major burnout of the high-voltage package.
Now, the game between Germany and Argentina is about to start. I packed up the tools, and the user agreed to watch the match together. He said he’d call me if anything else went wrong.
For beginners: When dealing with a color TV that has no picture, check the tube first. If the TV has been used for a long time, there might be multiple issues. First, make sure the +B voltage is normal. Then check the reverse capacitor and related circuits. If the TV uses a crystal oscillator, test it for leaks or abnormal excitation. Otherwise, if the upstream tube is turned on, the tube may blow again, causing unnecessary damage. Also, using a multimeter to detect line current—if you notice any abnormalities, disconnect immediately to protect the tube.
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