Audio and Video Equipment Servicing
Audio and Video Equipment Servicing
This domain tests audio chains, speaker matching, television signal and display sections, and systematic fault finding in audio and video products.
Core rules
- An audio chain runs source, preamplifier, power amplifier, cable and loudspeaker. Match speaker impedance to the amplifier rating; too low a load can overheat the output stage.
- Distinguish distortion, hum, hiss and intermittent output; each points to different stages.
- Analogue TV standards differ: PAL 625 lines/50 fields and NTSC 525 lines/60 fields. Modern sets handle multiple inputs through scaling.
- An LCD/LED TV has a power board, main board, T-con board, panel and backlight driver. Sound without picture narrows the fault.
- HDMI faults can be cable, port, EDID or firmware; test with a known cable and source.
- CRT sets store dangerous anode voltage; discharge correctly and never assume the set is safe when unplugged.
Worked example
An LED TV has sound but a dark screen. Shine a torch at the panel: a faint image means the panel and T-con are likely working, so suspect the backlight. Measure the LED string voltage at the driver; if it is at the boost limit with no current, an LED is open. If voltage is low, check the driver enable and dimming signal from the main board. A single open LED can shut down the whole string, so test individual LEDs or replace the strip set after checking driver current.
Traps
Replacing a panel when only the backlight is faulty; condemning a TV without testing the HDMI cable; ignoring firmware; connecting a 4 Ω speaker to an amplifier rated only for 8 Ω; touching a CRT anode.