Wednesday, November 14, 2012

Repairing 4H.V1448.481 backlight inverter board from Insignia-NS-LCD37-09

A year ago I posted an article about replacing the original inverter in Insignia NS-LCD37 LCD TV with 4H.V1448.481 since it was more available and cheaper.

Well since then the newly installed inverter has also failed - in fact twice - and the second time I opted to repair it as opposed to replace it since I already had a dud handy.

The same backlight inverter 4H.V1448.481 is used in a good number of other LCD TVs such as Philips 32PFL5322D/37, PROSCAN 37LB30QD, Sanyo DP37647 and in fact many more, so hopefully this will help others in same boat.

Failure symptoms were the same both times - display will lit up for a split second and will then turn black, the TV otherwise still operating properly.

Inspecting the inverter I found a blown SMD fuse - one of several along the length of the board - and that told me in which section the problem will be.

Here is how the fuse looks like:
As can be sen from the picture the fuse is 3A/32V and is driving two power transistors, each of which in turn drives a transformer on the board (well the last can not be actually seen on this picture; just take my word for it, ok?).

So there is one such fuse for every two power transistors / transformers and you will be looking for a fuse that is blown and does not have continuity.

Once I got the group, I first ruled out the power transistors by comparing them and finding out that they have the same resistance as all others.

The culprit turned out to be - not surprisingly actually - one of the two transformers although I could not figure which one until I put a more powerful fuse (5A as opposed to 3A) and tried to see what happens.
But I do not recommend you do that.

As it turned out, the bad transformer could very easily be distinguished once pulled out of its place and inspected on the back.

Here is what it looked like:

Clearly it was the primary winding that has burned and because it has low resistance I could not find the difference with a meter.

The board itself also had traces of burning:

Replacing the transformer with a pull-out from the first defective board restored full functionality....for now.

Hope this helps!


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