It's been a while since I last posted here. Today, I came back to share an emergency repair of a color TV that had no character display. I used the "shifting wood" method, which is more of a trial and error approach than actual technical expertise. The technician from Bo Jun just smiled and said, "If it doesn't work, don't even try to spray it."
I was working on a Changhong 1238 model TV with a CHT0827 CPU. The user reported a color issue, and upon turning on the TV, it turned out the system settings were wrong. But when I tried pressing the buttons, there was no response at all—seemed like the buttons were broken.
So I grabbed the original remote control and tried pressing the menu button, but nothing happened. Was the remote broken too? I used a remote detector and found that the remote was actually working fine. Then, by accident, I pressed the standby button, and the TV turned off. Pressing it again turned it back on. When I pressed the volume down button, the sound decreased, but there was no volume icon on screen. Worse yet, there were no characters displayed at all!
I opened the cover and took a closer look. I noticed that there was no inductor between the CPU crystal and no other inductors nearby. It made me think that maybe the middle part was the character oscillation inductor. So I removed the Zhongzhou coil and checked it—it wasn’t broken. However, one of the attached tubular capacitors was severely leaking, and its resistance was only around 20 ohms. I replaced it, and suddenly, the long-lost characters appeared on the screen!
But something still felt off. The characters were shifted to the upper right corner, not centered. I realized I needed to adjust the video position. I grabbed a 47PF blackhead capacitor from the high-frequency head and connected it. That helped a bit, but the characters were still slightly off the screen. So I took another 82PF blackhead capacitor from the same area and connected it in series with the 47PF. Now, the character display was almost perfectly aligned.
These two capacitors are normally used as IF output coupling capacitors in the high-frequency section. Since this TV didn't require RF reception, removing them didn't affect the overall performance. After that, I used the remote control to enter the menu and changed the color system from NTSC 4.43 to the automatic setting. Everything returned to normal.
It’s amazing how a small component can cause such a big problem. Sometimes, it's just about testing, adjusting, and being patient. This kind of repair always feels rewarding, even if it takes a few tries to get it right.
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