Sony KDL-40S4100 no backlight

[tibimakai]

I have picked up this nice TV, looks like new. It was packed almost like you would get it from the store for $60.
TV works OK, except no backlight. It has sound, image with flashlight, voltages are OK.
I don't have 2 sec. to black, it's completely dead backlight.
It's one big inverter transformer on the power supply and a bunch of small transformers on a separate board.
I have watched that Samsung similar setup which shows how to measure and bypass a bad transformer or ccfl tube.
I did not find anything bad there. All the transformers are the same resistance, 235ohm. Voltage at each test point is the same, if I wait a while it drops to 0.1Vacc. With the scope I'm getting a similar signal at all test points.
I feel like it's something very simple, I'm just over looking something.
Pictures are coming soon(camera is charging now).

[kevinm34232]

Re: Sony KDL-40S4100 no backlight

Gee thanks was looking for that video last couple days just found it tonight

Is there a BLON pin on that inverter?

[tibimakai]

Re: Sony KDL-40S4100 no backlight

Good call.
Yesterday I have done some measurement, but I forgot to write them down.
Nothing seemed out of place.
If I remember correctly there is one, but I will have to measure again.

[tibimakai]

Re: Sony KDL-40S4100 no backlight

Here are the pictures:

[tibimakai]

Re: Sony KDL-40S4100 no backlight

OK, I have the measurements for the CN303 connector:
BL-DET: 0.005V
BL-ON: 3.605V
BL-DIM: 3.325V
On the big capacitors I have 391V.

[tom66]

Re: Sony KDL-40S4100 no backlight

Check that 0.1 ohm resistor next to the large primary caps.

[tibimakai]

Re: Sony KDL-40S4100 no backlight

It's bad. I thought that I already checked that one and it was good. Weird. A great thanks Tom. How could I check it out if that fixes the problem? What would be the color code for a 0.1ohm/1w?

[tom66]

Re: Sony KDL-40S4100 no backlight

The colour code for this 0.1ohm appears to be "0.1OHM".

If it is bad, likely one of the diodes or FETs around there is short. Rare for it to simply fail open with no apparent short...

[kevinm34232]

Re: Sony KDL-40S4100 no backlight

Could that affect the backlights?

[tom66]

Re: Sony KDL-40S4100 no backlight

Easily. It provides the 391V for the backlight drivers, which drive the transformer, and generate the ~3.5kV. It goes without saying, do not attempt to measure the 3.5kV on a conventional DMM.

[tibimakai]

Re: Sony KDL-40S4100 no backlight

You were right, the diode(NXP BYC8X/600) it went south and the FET also(K3569=2SK3569). FET is available on Ebay.
The FET is not available at Digikey(it shoes up though), maybe it's a special order.
The diode is available at Digikey, but not sure which one should I get, there are two variants:
http://www.digikey.com/scripts/DkSea...=0&y=0&cur=USD

[tom66]

Re: Sony KDL-40S4100 no backlight

The diode is shaped like that? Or otherwise?

[tibimakai]

Re: Sony KDL-40S4100 no backlight

It is installed on the heatsink.

[tom66]

Re: Sony KDL-40S4100 no backlight

Ok, do the axial diodes near the green caps also test OK?

[tibimakai]

Re: Sony KDL-40S4100 no backlight

D312 is shot too. Man you are good. Noticed it though, but I thought that maybe it shows that way because of another component is connected in parallel. I was lazy to remove it to test it.
I was anxious to tell you about the other two bad components.
The FET is shot in every direction.
I haven't had a chance to look at the schematics and you are able to help me much faster. No need to check the schematics This way I won't learn , just kidding.

[tom66]

Re: Sony KDL-40S4100 no backlight

Maybe it's best to replace them all. For longer lifetime.

[tibimakai]

Re: Sony KDL-40S4100 no backlight

Which components shoud be replaced? Diode on heatsink, the other diode next to the green cap?

[tom66]

Re: Sony KDL-40S4100 no backlight

The four diodes and two fets.

[tibimakai]

Re: Sony KDL-40S4100 no backlight

OK, I have changed the two FETs, four diodes and the resistor and the TV is running great!
Has a very good picture this TV, I really like it.
Thank you very much for your help Tom.