40" RCA L40FHD41 No Picture + No Audio

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

on the transformers, resistance test the output pins that i have marked out.
no power applied during testing.

these are the output pins that drive each backlight ccfl. you would not put your meter anywhere near these with power applied. very high voltage.


check all of the transformers, top to bottom. the top one will have a different resistance to the others, but we still need to know how it reads. you are looking foe one output that is noticeably different to the others.

p.s. i'm guessing these pics are off of a phone, as they are tiny when i extract them to my desktop.

weird the resolution of those pictures are ~2600 x 3000,

resistance test would be ohm setting on my meter right?

I am grounding by black lead to metal chasis and red probe to pins, power cord is unplugged, inverter board connector is connected to PS board

this isn't giving me any readings...

Am i testing it right?

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

Idk if i tested it right, but, each transformer has 4 pins or 2 pairs of two. So i put black lead to 1 pin and red to pin next to it. Or was i suppose to ground black lead to metal chasis then check red?

I tried to do so and my meter only showed 1

So probing black lead to pin and red lead to pin testing for 200k OHMS i did manage to read 01.6 on all of the transformers except the top one, which i got 01.1 for the top

[budm]

Re: 40" RCA L40FHD41 No Picture + No Audio

There are two SMD fuses (white body with gold ends), both of them are good? You can check and see if you do have 24VDC at both ends with ref. to GND.

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

Budm, I think the fuses are good. Did an ohm reading on them and the results were 0.00 which is good right?

I still don't know how to test the transformers, I tried the output pins on them and got strange readings

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

I took the inverter board off to reveal the backside and it is definitely showing blemishes of high heat on the board, which leads back around to the top transformer, maybe even the 2nd one underneath it as well.

I took a picture of what i'm talking about and also the solder joints on the transformer to the board itself, looks charred up a bit...

[attainteddragon]

Re: 40" RCA L40FHD41 No Picture + No Audio

on the output side of the transformers (panel side), there are 4 pins, put one lead on the outer pin and one one the pin next to it. then do the bottom pair. i have one of these inverters here somewhere, but not sure where. i am fairly sure that is the right legs without having it infront of me. it will most likely be in the m-ohm range.

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

I think I am testing them correctly, certainly how you're instructing me; I am getting 1.058k OHMS on top transformer and 1.673k OHMS on the other transformers

The top transformer is about 2/3 the size of the rest of the transformers, so maybe that's a normal reading...

If i test the bottom pins which i assume may be the input side? I get .740 on the top inverter and ~1.300 on all the others

I also did a continuity test between the 4 pins and the top transformer is giving me readings of ~1050 and the rest of the transformers are reading ~1550

My meter beeps at me when touching the two middle pins on the top transformer (pins 2 + 3) so that circuit must be closed and good, yes?

However, testing the other 3 transformers, my meter wouldn't beep when touching pins 2 + 3...

edit

it's a surface mount board, i thought maybe you said to test panel side as in the back side of the inverter board

[attainteddragon]

Re: 40" RCA L40FHD41 No Picture + No Audio

each inverter has 2 output (which you are testing) and each output powers a ccfl globe in the panel.

i think you have 4 transformers, i can;t find a full pic of the inverter board.

can you relist the readings of each output pin from top to bottom like this. it will just make it easier to see values better for me.

1.058k
1.673k
1.673k
etc
etc


one other thing to note, when you removed the inverter, you pulled the board up from the ccfl sockets. you could of slid the board out from the plastic connection strip by pulling towards the ps board. unfortunately now, you will have to remove the panel to reseat the ccfl connections back into the connecting sockets.

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

T1 = 1.058k
1.058k

T2 = 1.637k
1.674k

T3 = 1.637k
1.638k

T4 = 1.637k
1.637k

These may be a couple of hundredths of an ohm off but those were the readings

That does suck but if the bulbs are bad it would need to come off anyways, but i did not know this :/

[budm]

Re: 40" RCA L40FHD41 No Picture + No Audio

Never mind, after looking at the pictures of T1, that may be normal reading then.

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

So if the transformers are good then the inverter board is good or can some other components on it still cause backlights to shut off?

[attainteddragon]

Re: 40" RCA L40FHD41 No Picture + No Audio

ok. bud is the expert when it gets down to the circuit side of things, so i may not be able to help much more.

there is most likely a feedback loop for each transformer that would let you know if a bulb isn't lighting up, but i'm not sure where you would test for it, and you would need the ccfl's hooked back up, which means opening the panel anyway.

could even be some balast caps inside that may have issues, but i can't say for sure.

if it was me, i would open up the panel and inspect the ccfl bulbs and connections, but i get very over zealous at times.

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

Update:

I've taken apart the panel and have access to the ccfl bulbs, they seem to just clip into a metal connector very simply. No soldering like i thought.

How do i tell if the bulbs are good or a problem at all? I see some carbon buildup on some of them near the tip.

Any advice on where to go from here, i greatly thank you.

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

If it were a better more expensive tv I would consider converting it to LED strips, these ccfl bulbs are $9USD each

Even if the bulbs were bad theres at least 12 bulbs, maybe only a few bad ones.

Honestly the TV, is probably worth more for parts, but i am still determined to fix it if I can.

If i can reach the conclusion that all the boards are good and working, the LCD display is GOOD, but if it costs too much to repair maybe i can part it out.

edit

there are plastic clips inside the panel behind the film light reflector screen, they hold the ccfl's in place, uniformly. However, the extreme heat made them brittle and some are breaking, which is making this slightly more difficult...

[attainteddragon]

Re: 40" RCA L40FHD41 No Picture + No Audio

if you have the panel out, have a look at the bulbs as they light up. curious if any don't strike properly.


the holders always break. as long as there is enough support to hold them in place then it is ok. i have glued them in place without any issues.

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

Looking at the light reveals only the left side (inverter side) lights up... There are 15 ccfl tubes total and all of them only light up half of each tube.

They all turn on/strike together but only half way.

If the bulbs aren't bad, everything I'm reading online says inverter board or more specifically the transformers or one of the transformers. Unless I'm not testing them right they seem to be giving good OHM readings

[budm]

Re: 40" RCA L40FHD41 No Picture + No Audio

That means the drive Voltage for the lamp is too low or the Lamps ground return has high impedance.
So it can be be Inverter board and will need indepth troubleshootihng.
Can we get the model number of the LCD panel to see how the other ends of the lamps are grounded?

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

I tested the two SMD fuses on the inverter board again with my DMM...

I get a reading of 0.00 resistance on both using, currently using this setting on my multimeter tool (see picture)

It's a 7A fuse and IDK if my red probe is in the right socket on my DMM

[ajsterr4]

Re: 40" RCA L40FHD41 No Picture + No Audio

Can we get the model number of the LCD panel to see how the other ends of the lamps are grounded?

Taken from backside of LCD panel

[budm]

Re: 40" RCA L40FHD41 No Picture + No Audio

When checking fuse, you will use the lowest Ohm scale the meter can do, in this case it will be set to 200-Ohm scale.
Please read post 77.