JVC LT-42EM59 no picture no sound

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

Pin 1 is BLon and that is bad, Pin 4 is the dim voltage and pin 5 is GND. Since we know this, now it is the time to check all voltage rails again on the other connector.
After that, I want you to be really careful as there could be more than 360V DC so be warned that in the primary you are connected to the mains. Take both leads of your DMM and measure the filter cap and see what voltage you get.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

I apologize, but which connectors would you like me to check voltage on now? Are you talking about the set between the power board and the Master backlight inverter?

With the TV just plugged in, or with after I actuate the power button?

Also, which is the filter cap?

Thank you for the patience.

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

O.k. download the schematic that budm provided in post 16. First page, the is a stamp that sez "Live". Underneath is the bridge rectifier and to the right there are 2 capacitors. Measure from C9011 negative pin to C9010 positive pin. You should have 375V or so cording to the schematic.

With the other connector I meant CN9005. Measure everything there again.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

I had time to grab the voltages on pins 1-15 again before work this morning. I will have to take the board loose to get to the cap pins later on today. Pin 15 was 24VAC, sorry for the messy hand writing.

have a good one

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

So to recap things in a nutshell:
Now the TV turns on but it doesn't have any backlight, right? So if you shine a flashlight into the screen, you should see a picture? In any case it won't be good if the backlight isn't working. The main board isn't sending BLon to the PSU, so we force it on. This way we can check if there is one or two problems and where the problem lies.

So unhook the main board again, leave the backlight connected, take two 1k ohm resistors and jump one from STBY 5V to PSon and the other one from STBY 5V to BLon. Plug the TV in and see if the backlight comes on.

[budm]

Re: JVC LT-42EM59 no picture no sound

He will need 3 resistors:
1 for the MAIN_POW pin 6 of CN9006.
1 for the PFC_POW pin 8 of CN9006.
1 for the BL_ON pin 1 of CN9006.
He also needs another one for the DC_DIM (pin 4), or PWM_DIM pin 2.
If he does have signals at MAIN_POW and PFC_POW, then he only needs to remove the BL-ON wire and do the backlights force on.

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

good catch... had forgotten about the PFC POW. lets see what he gets.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

I dont have any 1k ohm resistors, so let me grab some at radio shack today. I'll get you the results as soon as I can.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

Just so I understand and not just got through the motions:

Unplug CN9005 and CN9006. Place resistors between STB5V and CN9006 Pins 1,4,6, and 8. I'm guessing I use the male pins on the power supply board so that we can send power to the back light inverters??

Also, capleaker, i see no picture when I use a flashlight.

[budm]

Re: JVC LT-42EM59 no picture no sound

Find out first when you have everything all back up together to see if you do have these two signals first:
MAIN_POW and PFC_POW

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

smells almost like a new main board is needed then

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

I measured 0VDC with just the TV plugged in and after I pressed the power button, I still have 3.1VDC on each of those points.


So, now do I do the resistor checks like this?:0

Unplug CN9005 and CN9006. Place resistors between STB5V and CN9006 Pins 1,4,6, and 8. I'm guessing I use the male pins on the power supply board so that we can send power to the back light inverters??

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

or solder them on the bottom of the board. I wouldn't use the pins, as it is harder to clean them off afterwards.

[budm]

Re: JVC LT-42EM59 no picture no sound

"I measured 0VDC with just the TV plugged in and after I pressed the power button, I still have 3.1VDC on each of those points.:"
So you have 3.1VDC for the MAIN_POW pin 6 of CN9006.
So you hvae 3.1vdc for the PFC_POW pin 8 of CN9006.
You will leave every thing connected, but you need to remove the wire for the BL_ON pin 1 of CN9006 that goes back to them main board and then use a 330~1K resistor between pin 1 of CN9006 and the 5VSTBY Voltage to force on the backlights, the reason we need to remove the wire is we do not want to back feed the force on signal back to the main board.
Do the same for the PWM DIM and the DC_DIM pin since you also have 0Vdc on the PWM_DIM, DC_DIM pin.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

I ask for a day or two to get back to this project. Work has been keeping me very busy. I didn't want you to think I've abandoned this. Thank you for your patience.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

I have no wire in PWW_DIM.

I placed two resistors coming out the back of STB5V. One resistor jumped from there to DC_DIM.

I took out the wire from CN9006 Pin 1 (BL_ON). The other resistor went from STB5V to this pin location.

I plugged in the TV, pressed the power button and heard the click. It still clicks back "off" after about ten seconds. Still no picture. I cant see anything with a flashlight either. I did measure 5VDC at DC_DIM and BL_ON.

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

with the main board disconnected? You should be able to press the button on the TV as it is "hardwired" to On. Just plug the TV in and the BL should come on.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

I followed the instructions in budm's post #34, except for that I dont have that wire in PWM_DIM.

I left everything plugged in and just removed the BL_ON pin from the CN9006 connector, then added the resistors.

I turned off the lights and made the room completely dark so I could try to see if something would flicker when I pressed the power button...it seems like the backlight is what's flashing, once, for a fraction of a second when I press power. Then, ten seconds later or so, I hear the board click again and it has turned itself off.

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

O.k. I thought you were doing #26.
Unplug the inverter board and measure the output of each transformer (with your DMM in Ohms range)and compare them to each other. If one is out more than 3%, that's your candidate. There are 4 inputs and 4 outputs on each transformer. if the output is facing you, lets number them from left to right as 1,2,3,4. So measure 1-2,3-4 and 1-4 on each. If you find that a 1-4 reading is more than 3% to the other transformers, it is bad.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

Do I put everything back to factory positions, or do I leave the resistors in place? Is this with just the tv plugged in?

Thank you