LTV-32W6 HD has back-light issues with picture.

[Pioneerx01]

I am working on LTV-32W6 HD. It turns on fine, all the voltages on PSU are OK, has image with flashlight test only, but the back-lights are not coming on. TV "works" until you power it off, so there is no automatic error shut down that usually takes place on TV's with back-light problems.

When checking pins on the Inverter, all VBL and IL SEL are 24.65V, Grounds are good, BLON gives me 3.3V and fuses are OK. SEL and E-PWM are shown as grounded (or shorted to ground) I am not sure if that is normal and that is a questionable in my mind. When I unplug the cables, SEL and E-PWM are no longer showing as grounded.

I can't find out the purpose of SEL and E-PWM, but it seems like they should not be showing as grounded. In which case it would point to short on the main board. Am I thinking about this correctly?

Thoughts?
Thanks

[budm]

Re: LTV-32W6 HD has back-light issues with picture.

I-PWM is also 0VDC?

"SEL and E-PWM are shown as grounded" so they show as 0 Ohms.
I-PWM = INTERNAL PWM for backlights level control.
E-PWM = EXTERNAL PWM for backlights level control.
Only one of those two has to be selected.
What is the LCD Panel model number? I acn then look for the panel spec.
You should have Voltages at one of the PWM pins

[Pioneerx01]

Re: LTV-32W6 HD has back-light issues with picture.

When TV is off SEL = 0 ohm, E_PWN = 0 ohm, I_PWN ~ 13Kohm all measured to chassis ground
When TV is on SEL = 0 ohm (0V), E_PWN = 0 ohm (0V), I_PWN = 12.24Kohm (0.05V) all measured to chassis ground
Panel model number is V320B1-L01

[budm]

Re: LTV-32W6 HD has back-light issues with picture.

It is set for I-PWM and the main board is not sending the PWM signal to the I-PWM pin.
Disconnect that I-PWM wire only (that pin then should show >2vdc) and see if the backlights will come on and stay on.

[Pioneerx01]

Re: LTV-32W6 HD has back-light issues with picture.

Same issue. TV comes on, stays on, no back-lights, but picture is there with flashlight.
I read the voltage on the disconnected wire and it still reads 0.05V, and it is the same on the main board as well.

If I were to jump the BLON (3.3v) with the I-PWN (while the cable is disconnected from the pins) would that be a problem? It seems that I-PWN can take 2.0-5.0V.

[Pioneerx01]

Re: LTV-32W6 HD has back-light issues with picture.

Read that wrong (I think), it looks like I-PWM goes to 3.0V only. A resistor maybe?

[budm]

Re: LTV-32W6 HD has back-light issues with picture.

I-PWM is the pulse-width signal, around 200~300 Hz range. when you read with your DCV meter that will show the AVG DCV Voltage. The main key is that it cannot be 0V.
So with everything connected you do have 3VDC at the I-PWM pin? If that is the case, the Inverter board is getting all the correct signal, then you will need to dig deeper into the Inverter board to find out what is going on.

I will need the good clear pictures of the whole Inverter board next.

Which one of these is YOUR Inverter board?
http://www.shopjimmy.com/catalogsear.../?q=V320B1-L01

[Pioneerx01]

Re: LTV-32W6 HD has back-light issues with picture.

I get nothing on the I-PWM pin, connected or disconnected. The main board is not sending out any voltages to that pin in any case.

[Pioneerx01]

Re: LTV-32W6 HD has back-light issues with picture.

I have located the transistor on the main board that is responsible for sending the voltage to the I-PWM pin, and it is not functioning properly. It is so small and so close to other components, I do not have sufficient skill, dexterity or tools to replace something like that. And that is assuming that this is the only part not functioning properly. I believe it is safe to say that it is the main board issues.

[budm]

Re: LTV-32W6 HD has back-light issues with picture.

I have located the transistor on the main board that is responsible for sending the voltage to the I-PWM pin, and it is not functioning properly. It is so small and so close to other components, I do not have sufficient skill, dexterity or tools to replace something like that. And that is assuming that this is the only part not functioning properly. I believe it is safe to say that it is the main board issues.

So that is measured right at the I-PWM pin of the inverter board, right?
Then you can try using 1K resistor between 5VTSBY pin and the I-PWM pin to see if the backlights will come on.

[Pioneerx01]

Re: LTV-32W6 HD has back-light issues with picture.

I did try that with both 5V and 3.3V sources and I got nothing. same problem persists.

When I had the 5V pin jumped, I was was checking around the inverter board at random point and I can't seem to get any voltages on the board but the 24V. Which brings me back to changing out failed components if I find one. I won't be able to change those transistors even if I wanted to.

High res of the inverter board . This one is mine.

[budm]

Re: LTV-32W6 HD has back-light issues with picture.

OK, to the right of the CN2 BY PIN #12, there is a very small black fuse F1 with '20' printed on top, check and see if it shows <1 Ohms. That is the commonly failed fuse.

[Pioneerx01]

Re: LTV-32W6 HD has back-light issues with picture.

Holy $#!?, that is it. I jumped the fuse and the back lights came on. And that is without jumping 3.3V or 5V to the I_PWM with resistors.

The fuse in question; is it 20ma, 0.2A or 2.0A? I am not sure how to read it. I am sure that I do not have replacement like that around. I'll check other burned out components I have around to see if I can find a compatible fuse. At worst I will hot wire and external 5x20 fuse to the board. Or should I just bypass the fuse all together? Not really a sound decision, but at worst it will work.

I am very thankful for your time on this. I guess I could be more thorough on 1st diagnostic step of checking ALL (key word) fuses.

[budm]

Re: LTV-32W6 HD has back-light issues with picture.

If I rememember correctly that is 1.5A fuse with 36V minimum Voltage rating, I use PICO II fuse or 5X20mm fuse will be fine..

[Pioneerx01]

Re: LTV-32W6 HD has back-light issues with picture.

I took an amp meter to the fuse and it read only 40ma draw with back lights on. I found a 500ma fuse on other failed board, I can harvest that. It is a bit too much, but that is the closest I can get.

[budm]

Re: LTV-32W6 HD has back-light issues with picture.

the current draw may vary with how high the backlights level is set to, and also the surge current can also me higher when power is first applied. You can try the 1/2A to see how well it will hold up.
15 = 0.75A so 20 is higher than 0.75A.