TV sound no video DX L40 10A

[fatcat]

Re: TV sound no video DX L40 10A

I'm getting a somewhat stable reading at 0.23 v on the brown, but it does still fluctuate a bit.

[dick_barton]

Re: TV sound no video DX L40 10A

I would say the transformers are fine.

Take a read through the following.
https://www.badcaps.net/forum/showth...hlight=sem2107

[budm]

Re: TV sound no video DX L40 10A

I'm getting a somewhat stable reading at 0.23 v on the brown, but it does still fluctuate a bit.

Anything <1V is considered as LOW state so minor fluctuation does not matter, and since it is in mV your meter may be picking up noise.
You need to leave meter on that that pin when TV is OFF, then turn the TV on to see if the Voltage jumps up and how high.

[fatcat]

Re: TV sound no video DX L40 10A

Anything <1V is considered as LOW state so minor fluctuation does not matter, and since it is in mV your meter may be picking up noise.
You need to leave meter on that that pin when TV is OFF, then turn the TV on to see if the Voltage jumps up and how high.

Ok, I can try that. It went as high a 0.41v as low as 0.19v.

So basically it is either the inverter or the tubes. I just checked in a dark room and when I turn it on the screen lights up in a < shape. The right side lights up well and on the left it narrows to a point. With a flashlight the full screen has video. Since most of the tests on the inverter showed ok, I'm thinking it might be the ccfl tubes. The other thing would be if the icu is messed up. I really didn't want to open the screen. Any thoughts?

[fatcat]

Re: TV sound no video DX L40 10A

I checked the brown on start up and there were no big spikes or anything, reading were low.

I re-checked the screen at boot up in a dark room and approximately 3/4 of the screen lit up from right to left. It looked like all the tubes were lighting but it shuts off immediately so maybe the tubes just didn't have enough time to fully light up all the way to the left? This would indicate a bad inverter would it not?

[budm]

Re: TV sound no video DX L40 10A

https://www.badcaps.net/forum/attach...5&d=1527484887
BTW, both fuses are good?

[dick_barton]

Re: TV sound no video DX L40 10A

I have not tried this myself but in the link I posted (reading post #45) it says "I connected pin 7 to ground and the backlights came on and stayed on" If you're willing to try this it may show you whether or not you have problems with any tubes.

[fatcat]

Re: TV sound no video DX L40 10A

https://www.badcaps.net/forum/attach...5&d=1527484887
BTW, both fuses are good?

Yes, both fuses tested good.

I have not tried this myself but in the link I posted (reading post #45) it says "I connected pin 7 to ground and the backlights came on and stayed on" If you're willing to try this it may show you whether or not you have problems with any tubes.

I'll have to check that again. Might give it a try, thanks for the tip.

[fatcat]

Re: TV sound no video DX L40 10A

So I tried pin7 to ground and it didn't make any difference. If it was the tubes, it is unlikely they would all burn out at the same time so something should have lit up with this test.Thing is, the guy in the other discussion obviously had a good working inverter board so I'm thinking it has to be the board. I'm attaching a pic of the scorched back side of the inverter. The worst burn marks are under what looks like a set of 4 resistors.

[budm]

Re: TV sound no video DX L40 10A

https://www.badcaps.net/forum/attach...3&d=1527484887
You should check those 8-pin power MOSFET's Source and Drain pins closed by that small inverter transformer. Can you read the P/N on them?

[fatcat]

Re: TV sound no video DX L40 10A

Can you read the P/N on them?

4614
bv9v2h

The only test of mosfets I did was a continuity type test.

[dick_barton]

Re: TV sound no video DX L40 10A

Post #6 gives a link to a video showing how to test them if you want to do a double check.
It certainly looks as though the mosfets have overheated and I would be checking all the 0 ohm resistors in that area for open circuit

[budm]

Re: TV sound no video DX L40 10A

4614
bv9v2h

The only test of mosfets I did was a continuity type test.

So check the resistance between Source and Drain.
So what resistance does it show in continuity mode anyway (if the meter also shows resistance in continuity mode)?
I use Ohm mode to check resistance, continuity beep just telling you you have connection point 'A' to point 'B'

[fatcat]

Re: TV sound no video DX L40 10A

Post #6 gives a link to a video showing how to test them if you want to do a double check.

Using that method all mosfets checked ok, no beeps.

I would be checking all the 0 ohm resistors in that area for open circuit
Today 01:44 AM

Using the same method? They all beep.

[fatcat]

Re: TV sound no video DX L40 10A

So check the resistance between Source and Drain.

Can you explain how to do that?

[dick_barton]

Re: TV sound no video DX L40 10A

Here's the pinout of the Mosfet

[fatcat]

Re: TV sound no video DX L40 10A

What kind of readings should I be getting and should all those mosfets have approximately the same readings?

[budm]

Re: TV sound no video DX L40 10A

We are looking for low resistance reading between Source and Drain pin so just report the reading for those two pins for us to look at.

[fatcat]

Re: TV sound no video DX L40 10A

I'm not sure I'm testing right, I get a bunch of different readings and they fluctuate. I understand these are dual mosfets with 4 drains and 2 sources with 2 drains per source, so when testing do I put the red lead to drain or source?

[budm]

Re: TV sound no video DX L40 10A

You test in both directions with the meter, typical failure mode for the MOSFET is shorted circuit or low Ohm resistance reading between S and D, so just report what you are getting, make sure to read the meter correctly to see if it is showing in Ohm, K Ohm, or M Ohm.