I recently inherited a completely dead LG 32″ LCD TV from my parents. Apparently this TV set was working fine one day and completely dead the next. So I thought I would have a look and see if I could get it back up and running. Upon receiving the set the first thing I did was try and power it up. Nothing completely dead. No standby light nothing. Checked the fuse in the plug (obviously) and that was fine. Time to dig a bit deeper.
With the current symptoms the obvious suspect is going to be the power supply. The internet is strewn with examples of power supplies going bad in these TVs and people on eBay are even selling repair kits for anyone wanting to repair them.
After carefully removing the back panel I had managed to expose the power supply board. I must say a bit of a beast by all accounts. But if you think about the job it has this is to be expected. Fortunately most of the connectors were labelled with the expected output voltages. Probing around on these pins showed no voltage on any of them. Checking the mains into the board gave a reading of around 230V AC. Checking the voltage after the 5A fuse on mains input read nothing. Turns out this fuse had blown. Question is why?
On closer inspection smoke damage can be seen on the large heat sink holding the power transistor, bridge rectifier and rectifier diode on the input stage. My first thoughts were one of these may have been damaged but on closer inspection it turns out the smoke was caused by a 220 pF 2Kv ceramic disc capacitor just in front of the heat sink (shown in the image above directly between the transformer and the heat sink) exploding. Which explains why the fuse may have blown. Probing around the remainder of the input stage the other components appeared to be fine as far as I could tell. Turning my attention to the electrolytic capacitors (shown above) on the output stage I could immediately see a number of these were starting to show the tell tale signs of failure with at least three of them having significant bulging. So I decided I would replace all of them just as a matter of course along with the ceramic disc capacitor that had blown.
Once all of the new components had arrived and been fitted along with a new fuse I powered up the board on the bench and now had a 5V standby voltage present. After fitting the board back into the TV and a quick press the power button on the side and the TV sprung back into action. Result. So a nice easy fix this one. Total spend was about £3 whereas a refurbished power supply board runs to around £30. And for a TV only worth probably that in the first place it hardly seems worth it.
Mikes Electronics Blog 