TV sound no video DX L40 10A

[fatcat]

This tv has gotten progressively worse. Problems began with the tv not starting up but after unplug and replug and on off a few times it would start up and work fine. This was happening for a few months. The problem worsened in the last couple of weeks with a loud and high pitch almost whistling sound. The sound was coming from the inverter board second transformer from the bottom. Wedging a piece of cardboard in there would stop the high pitch noise but a static sound would come and go. After a couple weeks video just stopped suddenly. Now when turning on, to get the led to go blue I have to turn off and on 2 to 5 times, the screen will flash showing the input graphic and immediately the video goes off, no back lights. Sound is working ok. I tested the fuses and mossfetts on the inverter board and they were fine. Power board outputs to the mb seem to be ok. I am getting the proper 24volt output to the inverter but some of the top wires on the output to inverter have some strange readings. I'm wondering what the correct values would be for the yellow,orange, red and especially the brown wires? I am getting crazy readings on the brown from 120.0vdc when power off to over 300vdc when power on. The decimal place will jump back and forth on the mm display from the first to the last decimal point constantly and readings tend to fluctuate up and down. What's up with that??? Any help is appreciated. Thanks.

FYI: I fiddle with repairing electronics but am not terribly knowledgeable about how it all works.

[CapLeaker]

Re: TV sound no video DX L40 10A

O.k. it sounds like you have an inverter problem. On the PSU top right there are 2 connectors. Turn the TV on and measure the DC voltage on each pin. Post the pin out names with the DC voltages measured. A Brown, yellow or blue wire doesn't tell us much, we really need the pin out names.

If the BLon and Dim pin is good, I'd be checking the capacitors and compare the output winding each of the transformers on the inverter board.

Please post a picture of your inverter board, and another one of the top right corner of the PSU, so we have the pin out names.

[fatcat]

Re: TV sound no video DX L40 10A

Here are the pin outs. The yellow, orange, red, and brown wires do not have any names or values on the board that I can see. They are the first four colored wires at the top of the connector to the inverter.

From top to bottom along the right side of the board are three connectors.

The multicolored connector going off to inverter board. (Top to bottom)
Unlabeled - Yw - 2.917v
Unlabeled - Or - 2.903v
Unlabeled - Red -4.10v
Unlabeled - Br - 2.593 to 259.3 up to 3.260 and 326.0 The decimal point constantly jumps back and forth
from after the first number to before the last number. Reading just now was 326.31v
Gnd - Bk - 0V
Gnd - Wh - 0V
Gnd - Gy - 0V
Gnd - Pu - 0V
Gnd - Bu - 0V
24V - Gr - 25.11v
24V - Yw - 25.11v
24V - Or - 25.11v
24V - Red - 25.11v
24V - Br - 25.11v

Below that is a 14pin connector going to main board:
GND - 0V
GND - 0V
STB - 2.833V
5V_S - 5.00V
5V_S - 5.00V
12V - 12.34V
12V - 12.34V
GND - 0V
BR1 - 2.903V
SW - 4.10V
GND -0V
GND -0V
5V_M - 5.25V
5V_M - 5.25V

At the very bottom right is a 4pin connector going to main board:
4 - GND - 0v
3 - GND - 0V
2 - 16V - 16.52V
1 - 16V - 16.52V

Haven't checked any inverter transformer outputs yet but I did post a pic of the inverter board in the first post but it doesn't have the cover removed.

[budm]

Re: TV sound no video DX L40 10A

"Unlabeled - Br - 2.593 to 259.3 up to 3.260 and 326.0 The decimal point constantly jumps back and forth
from after the first number to before the last number. Reading just now was 326.31v" More likely to be mV, look at the meter really well, if it is really 326V you would have seen smoke by now.
Lets see the pictures of the inverter board and its connector.

[fatcat]

Re: TV sound no video DX L40 10A

More likely to be mV, look at the meter really well, if it is really 326V you would have seen smoke by now.

Ha, I was thinking that seemed a little too much. Why would the decimal point dance around like that? Inverter pics posted.

[dick_barton]

Re: TV sound no video DX L40 10A

Are there any brown scorch marks on the back of the inverter board.

Watch the following video and test the mosfets as shown, Power to the set OFF.

https://www.youtube.com/watch?v=2QTfOy4BUpU&t=651s

[fatcat]

Re: TV sound no video DX L40 10A

I did see that video and tested the board accordingly but everything seemed normal even though the back of the board is scorched exactly like his video. The ground points were also blackened like the video and I re-soldered them. After watching that video I thought for sure I had found the problem and was a little disappointed the components tested ok, ha.

[dick_barton]

Re: TV sound no video DX L40 10A

Have you checked that the resistance of each of the transformers windings match each other?

[dick_barton]

Re: TV sound no video DX L40 10A

Have you checked both the white ceramic fuses on the inverter board are OK

Inverter transformers

[fatcat]

Re: TV sound no video DX L40 10A

Have you checked both the white ceramic fuses on the inverter board are OK

Inverter transformers

Yes, the fuses checked out ok. Thanks for the little graphic, that was perfect. Here are the readings from top to bottom of the board:

1.04 k ohms
1.05 k ohms
0 ohms

1.47 k ohms
1.48 k ohms
0 ohms

1.51 k ohms
1.51 k ohms
0 ohms

1.52 k ohms
1.52 k ohms
0 ohms

[budm]

Re: TV sound no video DX L40 10A

Yes, the fuses checked out ok. Thanks for the little graphic, that was perfect. Here are the readings from top to bottom of the board:

1.04 k ohms
1.05 k ohms
0 ohms

1.47 k ohms
1.48 k ohms
0 ohms

1.51 k ohms
1.51 k ohms
0 ohms

1.52 k ohms
1.52 k ohms
0 ohms

Remove that 1.04K and look at the bottom side of the transformer.

[fatcat]

Re: TV sound no video DX L40 10A

Remove that 1.04K and look at the bottom side of the transformer.

Well, I would like to remove it but I am having a hard time to do so. My iron is not very good and my solder sucker isn't the best either. I don't have any braided wire but I could try with a regular copper power wire. I don't have a hot air pen either but I have used a heat gun to do a re-flow before. That might be a bit much in this situation. How would you remove it?

The transformer in question is smaller than the other three and is under less load, so would the values change or should they still be similar to the other transformers?

Do you feel confident that the inverter board is where the problem is? Replacements from China seem to be reasonably priced.

[dick_barton]

Re: TV sound no video DX L40 10A

The reading appear to be in line with one I have in front of me. Same model inverter board.
The last transformer (T104) measures 1.07K on the two windings. It's wire up slightly differently to the others and only drives two tubes while the others each drive 4 tubes. Had't noticed it until I saw your readings and then double checked.

[fatcat]

Re: TV sound no video DX L40 10A

The reading appear to be in line with one I have in front of me. Same model inverter board.
The last transformer (T104) measures 1.07K on the two windings. It's wire up slightly differently to the others and only drives two tubes while the others each drive 4 tubes. Had't noticed it until I saw your readings and then double checked.

So does that mean all transformers are within specs?

[dick_barton]

Re: TV sound no video DX L40 10A

Did you sort out the odd reading you gave in post #37

Unlabeled - Br - 2.593 to 259.3 up to 3.260 and 326.0 The decimal point constantly jumps back and forth
from after the first number to before the last number. Reading just now was 326.31v

Do your backlight flash when you first switch on the set?

[fatcat]

Re: TV sound no video DX L40 10A

Did you sort out the odd reading you gave in post #37



Do your backlight flash when you first switch on the set?

I'm assuming the reading was mv not v. I'll check again.

Yes, it takes a few tries to get the tv to turn on out of standby but when it does, the led turns blue and the screen turns on briefly and it shows the input mode in a little graphic, but the back lights then immediately shut down.

[fatcat]

Re: TV sound no video DX L40 10A

Ok, couple of things. First, I re-soldered the top two transformers and the values changed a bit. The small top one now shows 1.07 kohms on both outputs and the next one down shows 1.49 kohms on both outputs.

I put the inverter back in, booted the tv, screen flashed and back lights shut down. I re-tested the questionable brown wire on the psu output to inverter. In auto mode I get the readings like I first posted with the decimal jumping back and forth. I changed the mm range to mv manual and I get an out of range reading. Seems there is a problem there, but what? Could it be the psu capacitors?

[budm]

Re: TV sound no video DX L40 10A

That is ERROR pin for that Brown wire (Inverter connector) pin 11.Put meter on higher Voltage range than 200mV, put it to 2V, if it is still OL, then put in 20V.
https://www.badcaps.net/forum/attach...5&d=1527484887
It can be the inverter board or the lamps.

[budm]

Re: TV sound no video DX L40 10A

The reading appear to be in line with one I have in front of me. Same model inverter board.
The last transformer (T104) measures 1.07K on the two windings. It's wire up slightly differently to the others and only drives two tubes while the others each drive 4 tubes. Had't noticed it until I saw your readings and then double checked.

Thanks for the verification.

[fatcat]

Re: TV sound no video DX L40 10A

That is ERROR pin for that Brown wire (Inverter connector) pin 11.Put meter on higher Voltage range than 200mV, put it to 2V, if it is still OL, then put in 20V.
https://www.badcaps.net/forum/attach...5&d=1527484887
It can be the inverter board or the lamps.

You are right, I didn't catch that. I'm not sure what it means exactly. Does that mean the inverter sends out an error? I'm having a hard time getting a proper reading on that one. Values seem to change and fluctuate. I'll keep trying.