Author: Dai Zhongqun
Hello radio electronics enthusiasts! In the last episode, I talked about forty years ago, and I installed a Venus C37-401 fourteen-inch color TV. In fact, it took a lot of effort in the process of assembling and debugging color TVs! Let me tell you today.
▲The Venus C37-401 fourteen-inch color TV set installed by the author of this article forty years ago is currently watching normally.
In 1983, after preparing a full set of materials, before assembling them, I first repeatedly read the two books "Color TV Set" purchased from the service department of Shanghai TV No. 1 Factory, read carefully and repeatedly to master the essentials, so as to be confident.
▲ The author of this article repeatedly and carefully read the two books "Color Television".
The color TV to be assembled, a total of 496 components, according to the Jinxing C37-401 fourteen-inch color TV circuit diagram and the finished printed circuit board purchased from the service department of Shanghai TV No. 1 Factory.
Some of these components are foreign products, in order to ensure that "one shot starts", at that time I tested these 496 components, part by part, after confirming that they were correct, and then welded part by part, among them:
▲171 capacitors of various kinds;
▲189 resistors;
▲68 semiconductors (including manifold blocks).
▲39 pieces of various coil transformers
▲29 other devices
▲The author of this article recalls the hardships and fun of welding assembly in those years.
In the end, all the welding and assembly were successfully completed in 7 days and nights.
After the assembly was successful, in order to be foolproof, I carefully read the 14-inch Jinxing color TV "Maintenance Manual" purchased from the service department of Shanghai TV No. 1 Factory
▲ The author of this article carefully read the 14-inch C37-401 Jinxing color TV "Maintenance Manual" purchased from the service department of Shanghai TV No. 1 Factory.
According to the discussion on TV adjustment in the "Maintenance Manual", the coarse and general tuning are carried out when the boot is carried out, and the test card broadcast by the TV station is clearly received (it was 11 o'clock at night, the TV program was finished, and the Mengshan transmitter only played the test card)
After a burst of excitement, I saw that only black and white images could be displayed, and I checked the relevant information and estimated that the fault was in the decoding circuit.
The next day, I moved on this color TV to the power supply bureau laboratory not far away, and used the SR-8 oscilloscope to measure the signal waveform at TP301 and TP501, and they were all normal.
After returning home, I looked at the relevant chapters in the book "Color TV", and estimated that the fault was in the peripheral circuit of the decoding circuit integrated block TA7193.
After careful investigation, there may be a problem with the D305 diode in the reverse trigger circuit, measured with a multimeter, and sure enough, D305 broke down the short circuit,
Replace with a new diode of the same model, after confirming that it is correct, as soon as the power is turned on, "another village", the color test card broadcast by the TV station appeared (the test time has passed the broadcast time of the TV program), the scene is really "after the three armies are all happy", the heart is sweeter than honey, Titus is excited!
▲The color test card broadcast by the TV station shown in the picture received after troubleshooting the decoding circuit that year.
▲The author of this article recalls the joy after receiving the signal that year.
Of course, there have been various situations in the process of use, "soldiers come to block, water to cover", there were many things encountered at that time about "climbing the hill and crossing the hurdle", I will tell my friends in detail next time. Thank you!
(Copyright notice This article is the author's original work.) Text Chinese words and pictures, without the consent of the author, may not be reproduced and quoted)
June 20, 2023