Cable Digital TV Fault Maintenance Case Examples

Example 1

A group of users in a certain area reported that digital TV signals were intermittent in recent days. Maintenance staff went on-site for inspection. Using a field strength meter, they found that the signal level was normal. When measuring the input voltage of the addressable device, it was 42V, which was within the normal range (above 38V is considered normal).

The technician initially suspected a poor cable connector. After cutting and reconnecting, the same intermittent signal problem still occurred. Based on previous measurements showing normal signal level, the maintenance team shifted their focus to the power supply voltage and measured the voltage section by section along the cable connectors.

Eventually, they found that the output voltage of a 4A power supply unit (with alarm system) was only 48V (normal output is 60V). It was judged that the power supply unit was faulty, so it was replaced with a new 3A alarm-equipped power supply.

After reconnection, the power supply alarm was triggered again and the output voltage dropped to only a few volts. The technicians concluded there was a short circuit in the line. They then isolated each power-feeding branch in turn for troubleshooting. It was found that disconnecting one branch cable stopped the alarm.

However, after careful inspection of that cable, no obvious problem was found. When it was reconnected, the alarm reappeared and there was a significant voltage drop. The maintenance staff then disconnected the input terminal of the downstream power splitter on this cable, and the alarm stopped while the voltage returned to normal.

They suspected the power splitter was faulty and replaced it with a new one. After reconnection, the output voltage returned to normal and the fault was resolved.

This case shows that a short circuit in a power-feeding splitter can cause the output voltage of the 4A power supply to drop (even though it may still appear within a “normal” range). Although the distant addressable device can still work, it becomes unstable, leading to intermittent TV reception. Such faults are not very common, but maintenance personnel should pay sufficient attention to them in future work.

Example 2

A user reported mosaic (pixelated) distortion on some digital TV channels. Maintenance staff went on-site and measured the signal level, which was 66 dBV and normal. They checked the user’s indoor splitters and connectors and found no issues, but the mosaic problem persisted.

The technicians then checked the outdoor addressable device and measured the -5 cable connector for this user. The output level was 73 dBV, which was normal. However, the -5 cable from the outdoor point to the user’s home included more than ten meters of buried line.

It was discovered that at a manhole corner, part of the cable shielding had been damaged by rats, leaving only the copper core.

After replacing the -5 cable, the digital TV returned to normal.

This case shows that even when signal level measurements appear normal, damage to the shielding layer (such as rodent damage) can allow interference signals to enter easily, causing abnormal reception. Maintenance personnel must carefully investigate less obvious potential causes of faults. Only by thoroughly analyzing and identifying the root cause can better service be provided to users.