On Tuesday, February 2, 2016 at 6:11:03 AM UTC-5, Miguel Giménez wrote:
Hello

I'm trying to repair a dead LG 32LS570S LCD screen. The backlight work
OK, all the power supply voltages are nominal and the unit turns on and
off via the remote or the keypad, but there is no image. The service
manual says "change the main board", but first I want to ask here if
this is a known fault.

Thank you

--
Saludos
Miguel Giménez

There are four causes of your problem: bad main, bad LVDS cable, bad tcon, bad display (display and tcon are often combined in cheap TVs). You can either start buying parts and throwing them at the TV or you can scope for differential signals and check the dc buck converters at the main and tcon for proper voltages.