ProScan PLED5529A-C: No image, Backlights good

[good_ol_Wes]

I got my hands on a broken 55" ProScan LED TV. I used this site heavily to determine that the original issue was that there was a burnt out backlight LED that would cause all the Backlight LED Strips to fail/turn off. I replaced the backlight strips and put the TV back together. Now when I turn the TV on, no image shows during startup (not even manufacturer logo shows up) and the screen is black. it is very obvious that the backlight LED's are working perfectly fine and on, but now the screen will not show images. Before replacing the backlight strips, I was able to see images on the TV when shining a flashlight on the screen at an angle, so I know the screen worked before replacing the backlight strips. can anyone help me determine what the problem is now/how I can go about determining the problem?

[vinceroger69]

Re: ProScan PLED5529A-C: No image, Backlights good

have you tested the voltage on both sides of the tcon fuse marked p 2016 also maybe worth removing one end of a ribbon cable on the tcon and turn the tv on do you get a image on half of the screen? then try the test with the other ribbon cable removed.

[good_ol_Wes]

Re: ProScan PLED5529A-C: No image, Backlights good

I checked the voltage going through P2016 = o.oV. I also tried removing one end of the ribbon cable, with no changes. tried the other side, nothing happened. its hard to tell if anything changes since the screen is black with no image on it.

[budm]

Re: ProScan PLED5529A-C: No image, Backlights good

0V on both ends of the fuse with ref. to the chassis GND? If that is the case, then
the main board is not sending the switched 12V to run the T-CON.
I would inspect solder joints of that black multi-pin connector that link the PS board and the main board, look real close with magnifying glass or re-solder them all.

[good_ol_Wes]

Re: ProScan PLED5529A-C: No image, Backlights good

ok with reference to ground I measure 8.25V across P2016, so it looks like Tcon is getting power afterall

[budm]

Re: ProScan PLED5529A-C: No image, Backlights good

ok with reference to ground I measure 8.25V across P2016, so it looks like Tcon is getting power afterall

What do you mean 'ACROSS' when it is being measured ref to GND?
So black probe on the chassis, red probe on one end of the fuse and you get 8.25VDC, the you move the red probe to another end of the fuse you also get 8.25VDC?
The reading should be 12VDC for 55" panel.
http://www.shopjimmy.com/catalogsear...an+PLED5529A-C

[CapLeaker]

Re: ProScan PLED5529A-C: No image, Backlights good

Are you sure that the LVDS cable from the main board to the TCon isn’t in backwards on the TCon side?

[good_ol_Wes]

Re: ProScan PLED5529A-C: No image, Backlights good

Yes Budm, you are correct. Digital voltmeter set to Volts DC, black probe touching chassis, red probe on either side measures 8.25-8.30 Volts. Where did you you find that information on shopjimmy.com? I looked all over the website and couldn't find details like that.

Yes I am positive that the LVDS cable isn't backwards because the connect only allows you connect one way. you cant flip it over and connect. you can flip sides on the main board side, but that does nothing but send 1 volt to TCon.

if Budm is correct (and I am assuming you are since your the expert) then it sounds like I'm losing a couple volts somewhere and that the TCon board isn't getting enough power to run. I measured the volts on both sides of the LVDS cable and they both read 8.3Volts, with reference to ground (chassis). there are two thin red wires on the LVDS cable, one read 8.3 Volts, the other read 0 volts, on both ends of the cable.

[budm]

Re: ProScan PLED5529A-C: No image, Backlights good

You can verify what the T-con Voltage and the Current requirement are by looking up the spec sheet for your LCD panel.

[budm]

Re: ProScan PLED5529A-C: No image, Backlights good

https://www.badcaps.net/forum/attach...5&d=1510525482
Did you inspect the solder joints of of the black connector that links the main board and the power supply board as my suggest in post #4, it is known for bad solder joints due to poor mechanical support.
There is 12V power supply in that power supply board, it is fed to switched MOSFET that feed the T-CON board, so make sure you do have 12V to begin with, look at that black connector pin 13 & 14 on the power supply side and on the main board side.

[CapLeaker]

Re: ProScan PLED5529A-C: No image, Backlights good

it may be that there is something shorted on the TCon and dragging the line down. So you may want to disconnect that too and check.

[good_ol_Wes]

Re: ProScan PLED5529A-C: No image, Backlights good

I inspected the solder joints of the black connector under magnifying glass. they all seemed to be fine. I measured the voltage on pin 13 & 14 on both mainboard and power board sides. when referencing the picture I posted, starting from the bottom (closest end to power cord) pins 13 are: 12V,3V 3.75V,0V,0V,0V,5V and is the same on both power and main board sides. I could not accurately measure pins 14, because of difficulty accessing the pins (I don't have steady enough hands to reach between the upper 13 pins to get to the lower 14 pins).

How will disconnecting the TCon board help? I did and nothing changed. where am I supposed to be measuring?

Kemmnok: what do you mean the black connector wasn't linked to the main board? like there wasn't a solid connection or that it was not a bridge between boards? did you have a Proscan PLED 5529A-C too?

so I see 12V going from power board to main board, but somewhere on the mainboard it steps down to 8.25V before it reaches the LVDS cable and eventually the TCon board.

[budm]

Re: ProScan PLED5529A-C: No image, Backlights good

So you do have 12V on teh power supply board side and 12V on the Main board side?
'Kemmnok: what do you mean the black connector wasn't linked to the main board? ' he means that there was connection problem due to bad solder joints so the Voltage from the power supply board do not get to the main board side, which as I indicated as the common failure.
'How will disconnecting the TCon board help? I did and nothing changed. where am I supposed to be measuring?' you will first find out which pin of the T-CON connector on the main board wire is the one that is connected directly to the surface mount fuse of the T-CON board, then you just check the Voltage on that pin of the main board when the T-CON connector is removed to see if the 8V will swing up to 12V or not, but At this point it looks to me that if you do have 12V feeding the board but you are only getting about 8V at the T-CON then I suspect bad switched MOSFET on the main board as the problem. Locating that switched MOSFET on the main board is not going to be easy for beginner.

[good_ol_Wes]

Re: ProScan PLED5529A-C: No image, Backlights good

Yes 12V on both the power supply board and the main board. Ok since I get power on both sides, that means that the black connector is ok. I found out which pins of the connector cable (main board side) send power down to the surface mounted connector on the T-CON board. When the T-CON board is connected: the pins read 8V. When the T-CON is disconnected it jumps up to 12V.

If it is a bad switched MOSFET, any tips on how to ID the one affected?

[budm]

Re: ProScan PLED5529A-C: No image, Backlights good

Check the resistance (200 Ohm scale) between any of the two red wires 'A' (connector in place) and 'B', 'A' and 'C'.
I expect one of the reading will show <1 Ohms (depends on your meter's resistance).