Humax 40″ LCD TV repair

Introduction

I was taking a walk with my girlfriend when we came by a house with a 40″ LCD TV standing against the wall outside, on our way back to the apartment the TV was still standing there. I knocked on the door and asked if I could take it if it was just for the trash. I got it for free and they spared themselves a trip to the recycle station.

Dragging the 38 Kilogram heavy TV home was a less pleasant part of this great deal

 

Safety

WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.

Read this document about safety! http://www.pupman.com/safety.htm

What to look for

I turned the TV on and got a picture with no signal noise, but the back light was flickering at about 10 Hz making the picture absolutely useless to watch.

Taking the TV apart was no problem, just some few 30 screws around the frame and we are inside to view a main board and a power supply board.

Previous knowledge tells me that if there is a picture, noise or not, on the screen, the main board is okay. Looking at the power supply board it quickly became clear where the problem was to be found. 3 clearly popped CapXcon capacitors is likely to be the fault.

The red circles on the above picture shows where the three capacitors were located. The two large capacitors are the smoothing capacitors for the 24VDC supply to the back light inverter boards, these were measured to only 300uF capacity. The reduced capacity to around 1/5 of the original explains the ripple current in the 24VDC supply that makes the inverter boards emptying them before the power supply board can charge the capacitors. Thus making the back light flicker.

I found some 2200uF capacitors that I de-soldered from other electronics to replace the popped CapXcon capacitors, turning the TV on revealed that it was fixed and now able to show a steady picture.

All I used was some common electronics knowledge, a soldering iron and 3 capacitors that I had from other old electronics.

Bottom line: I got a free 40″ Humax LDE-40A LCD TV and spent about an hour repairing it.