RCA TV no picture, replaced all boards. Backlight ok

[budm]

Re: RCA TV no picture, replaced all boards. Backlight ok

""I checked the voltage at the main board with and without the LVDS cable connected. There was not 12v anywhere. (The highest was about 2.3v) The cable is not damaged or pinched." Since you do have 12V at the power supply, then you should have 12V at the connector of the main board. If you do have it at the connector then you have problem on the main board somewhere.

[Bfritz97]

Re: RCA TV no picture, replaced all boards. Backlight ok

Hello?

[Bfritz97]

Re: RCA TV no picture, replaced all boards. Backlight ok

So does this mean that the power supply is ok? And the main board is telling it to turn on, but could something else be wrong on the main board?

[budm]

Re: RCA TV no picture, replaced all boards. Backlight ok

You correct Voltages (Standby 5VSB, switched 5V, switched 12V, and STB (PS-ON) signal).

[Bfritz97]

Re: RCA TV no picture, replaced all boards. Backlight ok

From top to bottom (bottom being where CON5 is printed):
12.25
12.25
-0.02
-0.02
-0.02
5.08
5.08
5.1
4.23
5.08
5.08
-0.03
-0.03
This is on the main power board at the main connector. It is the only connector that has voltages printed next to it

[budm]

Re: RCA TV no picture, replaced all boards. Backlight ok

"I checked the voltage at the main board with and without the LVDS cable connected. There was not 12v anywhere. (The highest was about 2.3v) The cable is not damaged or pinched."
You have to have the switched 12VDC (It will be present when the power supply board receives the PS-ON from the main board) from the power supply board to feed the main board, then that 12V is fed through the switched Power MOSFET to supply the 12V to the T-CON when TV is powered on. The 12V is also used by the Audio circuit.
You should also report the DCV reading of each pins of the connectors of the power supply to see what you have and what you do not have.
Also post closed up pictures of this MEGMEET MLT-198TX power supply connector without the cable in place so we can see the labels of the connectors' pin.

http://www.shopjimmy.com/megmeet-mlt...wer-supply.htm

[Bfritz97]

Re: RCA TV no picture, replaced all boards. Backlight ok

Common issue on them panels is a shorted ceramic cap on the Tab bond driver Pcb which blows Tcon fuse. Do you know how to check for S/C ?

No, I'm not sure how although the tcon fuse is not blown

[ReeceyBurger123]

Re: RCA TV no picture, replaced all boards. Backlight ok

Common issue on them panels is a shorted ceramic cap on the Tab bond driver Pcb which blows Tcon fuse. Do you know how to check for S/C ?

[Bfritz97]

Re: RCA TV no picture, replaced all boards. Backlight ok

I checked the voltage at the main board with and without the LVDS cable connected. There was not 12v anywhere. (The highest was about 2.3v) The cable is not damaged or pinched.

I found the U3 voltage regulator. How could I test that? There are 3 terminals on one side and one large one on the other.

I tried to find the firmware update, but was unsuccessful. When I put in the serial number on RCA's website, it says the firmware is up to date and does not give me any other options. The website I tried was http://rca4tv.com/ The serial number of the TV is 2001-46la45r-a100238 if anyone can find the firmware.
The backlight does not automatically dim.

[dick_barton]

Re: RCA TV no picture, replaced all boards. Backlight ok

If there is no +12V on the Tcon then you need to find the reason why. There is an AM1117 (U3) voltage regulator on the main board which may be worth checking out.

[Diah]

Re: RCA TV no picture, replaced all boards. Backlight ok

why you do focus on the picture only which it had many steps and boards involved with it, just consider on the sound, if you get it the picture will be easy next step.

1- did the back light when it turn on after2 second dimming down or still same level ?

in case they are steady at light no dimming it mean the epprom didn't work as usual when no signal ordered dimming. and here we are at the same place that no sounds.

dont believe on any used boards you replaced that are free of fault unless you test them by your self and confirm they are fine.

epprom fault always going on 3 main fault.
a bad boot sector
b- bad corrupted boot software
c- bad soldering.

start and focus on this points you will be fine.

Tips:

to confirm epprom first flash the firmware on it with direct method, no need screen working.

go to the page of RCA to download the last firmware by interning the serial NO of your TV

put the software on USB root, IMPORTANT USB must not more 2GB, and empty,
turn off the tv and insert the USB disk in the services USB Port located at the side panel. then turn on the TV, you will have the TVs LED red and blue shining. give enough time for this upgrade process.

[dick_barton]

Re: RCA TV no picture, replaced all boards. Backlight ok

Check that you haven't pinched the LVDS cable wiring under the metal frame that it goes under.

[martino]

Re: RCA TV no picture, replaced all boards. Backlight ok

I would measure the voltage of the lvds cable at the mainboard side,then unplug lvds cable and measure again,see if its the tcon dragging the 12 volt down or not.Or a break in the cable itself perhaps.

[Bfritz97]

Re: RCA TV no picture, replaced all boards. Backlight ok

Update:
I found voltage markings on the power supply (next to the connector to the main board). All of the pins had what was written (5v or 12v respectively). I then followed that cable to the main board and checked the voltages again. I found 4 pins with 5v and 1 with 12v, so everything seems good there. I then checked the voltages at the LVDS cable at the TCON board. There was nothing higher than 1.4v on any of the pins.
So I suspect the main board is no good, but is there anything else I can do to confirm this?

Thanks

[Bfritz97]

Re: RCA TV no picture, replaced all boards. Backlight ok

Just to be sure,your volt meter on dc ,black prone on metal ground red prone on one side of fuse,then other side of fuse. Both sides 0.5 volts? Or 12 volt one side,0.5 other side?

Yes. Black on metal and red on the end of the fuse. Both at about .5 or .6 volts. Right above the fuse is says 125v ~3 amp I think

[martino]

Re: RCA TV no picture, replaced all boards. Backlight ok

Just to be sure,your volt meter on dc ,black prone on metal ground red prone on one side of fuse,then other side of fuse. Both sides 0.5 volts? Or 12 volt one side,0.5 other side?

[Bfritz97]

Re: RCA TV no picture, replaced all boards. Backlight ok

I was wrong. There is only about half a volt at the tcon fuse. Also, I'm fairly sure I ordered all the boards by part number and they look identical to the old ones.

[jetadm123]

Re: RCA TV no picture, replaced all boards. Backlight ok

Since you replaced all the boards, did you verify that the t-con and main boards were the corrects ones for your set?

[Bfritz97]

Re: RCA TV no picture, replaced all boards. Backlight ok

You will need to find out if you get DCV at both ends of the SMD fuse on the T-CON board with ref. to the chassis GND.

I believe I checked this at one point and there was voltage at both ends, but I will confirm that when I get home today and report the exact voltage as well

[budm]

Re: RCA TV no picture, replaced all boards. Backlight ok

You will need to find out if you get DCV at both ends of the SMD fuse on the T-CON board with ref. to the chassis GND.