Emerson LF501EM4F turn on then off.

[erickeri1234]

Re: Emerson LF501EM4F turn on then off.

No cable between the power supply board and the main board, LED connector in place, do the resistor jumper for the PS-ON (P-ON-H2) as before, then another resistor between the jumper J106/ BL-SW and the 3.3V to force the backlight on, see if the backlights will stay on.
Pictures provided by shopjimmy.
http://www.shopjimmy.com/emerson-a3a...pply-unit.htm#
Emerson A3AU0MPW-001 Power Supply for LF501EM4 / LF501EM4F

OK I jumped 3.3v to j106. But backlight didn't come on.

[SLK001]

Re: Emerson LF501EM4F turn on then off.

Here's a good set of schematics for this board.

https://www.badcaps.net/forum/attach...1&d=1463019635

[erickeri1234]

Re: Emerson LF501EM4F turn on then off.

It might be my testing. Imy having a hard time finding a 1k resistor. From 3.3v to p-on_h2. I'm getting at the end of the resistor 3.3v but once I touch it to p-on_h2 it drops down to 2.0v. Which might be to low.

[erickeri1234]

Re: Emerson LF501EM4F turn on then off.

Here's a good set of schematics for this board.

https://www.badcaps.net/forum/attach...1&d=1463019635

Ty I'm having a hard time reading it. Little blurry

[budm]

Re: Emerson LF501EM4F turn on then off.

It might be my testing. Imy having a hard time finding a 1k resistor. From 3.3v to p-on_h2. I'm getting at the end of the resistor 3.3v but once I touch it to p-on_h2 it drops down to 2.0v. Which might be to low.

So when you put the resistor between the 3.3v and the P-OB-H2, do get the DCV at the P-ON 21V? if you do then the power supply is being forced ON OK. You did use 1K resistor, right? 2V should be more than enough to turn on all 3 switched Transistors on that power supply board.
Looking at the diagrams:
PROTECT 3 is the error signal generated by the backlights circuit to tell the main board the condition of the backlights circuit.
PROTECT 1 is the error signal if the power supply lost the AMP+13V or p-on+21V.
Normal condition the DCV at PROTECT 1 and 3 should be around 2~3VDC, <1V = bad.

[budm]

Re: Emerson LF501EM4F turn on then off.

Here's a good set of schematics for this board.

https://www.badcaps.net/forum/attach...1&d=1463019635

Do you have the rest of the service manual or the download link? Thanks!
I download this one and it looks the same.

[SLK001]

Re: Emerson LF501EM4F turn on then off.

Do you have the rest of the service manual or the download link? Thanks!
I download this one and it looks the same.

I downloaded from here

There is only the power supply that I found, but I had to search by the board number. You might be able to find more data with a search by board number of interested components.

[erickeri1234]

Re: Emerson LF501EM4F turn on then off.

So when you put the resistor between the 3.3v and the P-OB-H2, do get the DCV at the P-ON 21V? if you do then the power supply is being forced ON OK. You did use 1K resistor, right? 2V should be more than enough to turn on all 3 switched Transistors on that power supply board.
Looking at the diagrams:
PROTECT 3 is the error signal generated by the backlights circuit to tell the main board the condition of the backlights circuit.

PROTECT 1 is the error signal if the power supply lost the AMP+13V or p-on+21V.
Normal condition the DCV at PROTECT 1 and 3 should be around 2~3VDC, <1V = bad.

OK just picked up 1k 1/2 watt resistors. Tested it all over again.
Jumped 3.3v to j106/bl-sw with 1k resistor getting 3.2v there.
Jumped 3.3v to ps-on_h2 with 1k resistor getting 2.4v on ps-on_h2.
I'm getting 21v at p-on+21v and I'm getting 12v at amp+13v.
So PS is on.
I do have the backlights plugged in and they ARE NOT lighting up..

[budm]

Re: Emerson LF501EM4F turn on then off.

OK , you need to look for the BACKLIGHT-ADJUST jumper (BL-ADJ J137), it should have around 2~3VDC on it, if not we will need to use another resistor.

[budm]

Re: Emerson LF501EM4F turn on then off.

OK, I look at the diagram, it does not have any pull-up resistor for the BL-ADJUST, so you need to add another 1K between the BL-ADJ and the 3.3v stby.

[erickeri1234]

Re: Emerson LF501EM4F turn on then off.

OK, I look at the diagram, it does not have any pull-up resistor for the BL-ADJUST, so you need to add another 1K between the BL-ADJ and the 3.3v stby.

OK jumped bl-adj/J137 and backlight is on...

[budm]

Re: Emerson LF501EM4F turn on then off.

And they stay on as long as the AC is applied to the board?
Also check the DCV at the PROTECT 3 jumper to see if it has 2~3VDC on that jumper.
BTW, it the PROTECT 3 signal is OK, then we will need to look at PROTECT 1 signal.

[erickeri1234]

Re: Emerson LF501EM4F turn on then off.

And they stay on as long as the AC is applied to the board?
Also check the DCV at the PROTECT 3 jumper to see if it has 2~3VDC on that jumper.
BTW, it the PROTECT 3 signal is OK, then we will need to look at PROTECT 1 signal.

OK I just had the backlight on for 10 minutes no problem. Stayed on the whole time. I checked protect 3 in like 4 different spots but I'm not getting any voltage. The spot for protect1 there is no jumper there it only shows this sign. - - - - - - - - - - -

[SLK001]

Re: Emerson LF501EM4F turn on then off.

Zero volts on PROTECT3 indicates a failure mode for the LEDs. Are you sure all the backlight strings are on, or just one of the three, or two of the three? Pin 7 of the LED controllers are all tied together, so if one fails, PROTECT3 will be pulled to ground, indicating a failure mode.

I'm afraid that you're going to have to crack her open and examine those LEDs.

[erickeri1234]

Re: Emerson LF501EM4F turn on then off.

Yep I think I'm going to do that. Open her up and see for sure

[erickeri1234]

Re: Emerson LF501EM4F turn on then off.

Well I pulled it apart and guess what I found. Yep one strip of L.E.D's are not working. So I tested it with one of the other plugs. It acts up sometimes it comes on sometimes it doesn't and I see one led out on the strip but after like 10 secs it starts to flicker and it comes on.
I looked on ebay there is a set but they say Samsung these in mine are LG. but they look identical.

[SLK001]

Re: Emerson LF501EM4F turn on then off.

Samsung LEDs usually have the cathode on the larger pad. LG LEDs usually have the anode on the larger pad. DO NOT modify the pads to fit one where the other should go. The pads are the primary heatsink for the LEDs, which are usually driven to the max, thus requiring all the heatsinking that they can get.

At the head of the strip, you should see a (+) and a (-) and two small test points. Use your ohmmeter to determine which pad is which.

[erickeri1234]

Re: Emerson LF501EM4F turn on then off.

Samsung LEDs usually have the cathode on the larger pad. LG LEDs usually have the anode on the larger pad. DO NOT modify the pads to fit one where the other should go. The pads are the primary heatsink for the LEDs, which are usually driven to the max, thus requiring all the heatsinking that they can get.

At the head of the strip, you should see a (+) and a (-) and two small test points. Use your ohmmeter to determine which pad is which.

Pic

[SLK001]

Re: Emerson LF501EM4F turn on then off.

Have you identified the bad LEDs yet?

[erickeri1234]

Re: Emerson LF501EM4F turn on then off.

No not sure on how to test it. I seen what strip is having the problem but there are 2 boards on the strip.