Haier TV repair case; TC-2125C TV can search automatically, but does not remember 23.
### Fault Phenomenon:
Pressing the PRE key enters the automatic search mode. The TV cannot identify and memorize the test signals emitted by the signal generator, but it can accurately memorize subsequent TV programs.
### Fault-Related Circuit:
Peripheral circuit of N101 (LA7680).
### Fault Location:
Variable VD06.
### Methods, Techniques, and Tips:
The function and role of the consistency detector and consistency detection signal.
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### Analysis and Repair:
Manually searched for channel 1's program. The image had severe horizontal drift, and the sound was intermittent. It was suspected that the output signal from the consistency detector might be faulty, causing alternating periods of silence and normal audio. Upon measuring the voltage at pin 30 of N101 (LA7680), which is the output end of the consistency detector, the voltage was unstable: 7V when sound was present, and 0V when there was no sound. Analyzing further, the consistency detection signal originates from the line and field synchronization separation circuit, so the fault should lie in the video signal at pin 33 of N101.
It was found that everything worked normally under AV input mode. Additionally, during format conversion, it was noticed that the automatic search function worked correctly in S-3 state, with no horizontal drift while watching. This indicated that the issue still occurred in the PAL system common circuit. Suspecting VD06 to be defective, its terminals were directly shorted with tweezers. As a result, normal sound and image appeared in both S-1 and S-2 states. After removing VD06 for measurement, it was found that its forward resistance was too high. Replacing VD06 (1K188FM1) resolved the fault.
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### Haier TV Repair Case:
TC-2125C TV can perform an automatic search but does not memorize channels.
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### Beijing Haier TV Repair Center
整理日期：August 10, 2011
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### ★ (Line) Consistency Detector (or Conformance Detector):
Initially mainly used in ICs produced in Europe, it is now widely integrated as a unit circuit in the line-field oscillation circuit. The consistency detector primarily checks whether the TV has received a television (or video) signal and whether the TV is in (line) synchronization. Generally, the output signal of the consistency detector can indicate the presence or absence of a TV signal, thus serving as various control signals. Besides being sent to the CPU, it can also be directed to other circuits within the TV. For example, it can be directly sent to the audio circuit as a noise reduction control signal or used as a control signal to temporarily disable the AFT (Automatic Fine Tuning) in the high-frequency head during channel switching.
The English name for the consistency detector is **COINCIDENCE DETECTOR**. Common abbreviations in circuit diagrams include **COINDET**, **COINC DET**, **COINCID DET**, **COINODENCE DET**, **DEENCF DET**, **TV TRANSMIDENT** (TV Signal Transmission Identification), etc.
