Power to board, no lights, will not power up.

This is a common problem for LG 42LN5xxx & 47LN5xxx LED TVs, the problem is defective LED back lights strips, it has nothing to do with main power supply & the main board.

Back - light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis. http://electro-medical.blogspot.com/
To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement. To some models sets, the back-light inverter and SMPS section circuit will be integrated at its main board itself. If so; the main board should be replaced. To some models of sets, all these section circuit will be integrated at its main board. If this is the case, you have to replace the main board.

Board is shot. Unless there is a cylinder fuse on board....but probably not.

bad power board

No one turned off your power switch up above the refrigerator, I trust. So, either your power supply or your main PCB is blown. Check the fuse on the main PCB (up on top of your refrigerator in the compressor area). The fuse will be right next to that round, black piezo electric speaker on the main PCB board as shown here:



If that's not it, then check to see if your power supply board is supplying power by measuring the voltage on JP11 of the Main PCB. You should see 26 vdc between pin 3 (GND) and pin 1. And, you should see 12 vdc between pin 3 (GND) and pin 2.

If you don't get those voltages, then you might have a bad Power Supply Board. It looks like this:


Also of note, your 120vac going into the Main PCB board comes in on JP8, pin 1 (WHT) and pin 5 (RED).

I don't know if you will be able to see the larger image of the schematic, or if Fixya will just give you a thumbnail, but I'll try to post it here, anyway:



Well, good luck and let me know if you need any more assistance.

these could be power supply , main board or both.

Hi,

It is possible that there is a problem with the connection from your power supply going to the main board of your laptop.
This is rather a technical problem and my best recommendation is to bring your laptop to a technician and have them check it.

Hope it helps!

Thanks!

It may be a fuse-resistor in the supply, FP5901. Test it.
If there are some questions - please on the mail - [email protected]

From Russia with love ;)
Vitaliy

Hi,

The blinking light means the controller QA01 in the AV_TERM system board is booting and driving the TIMER/REC RED LED light accordingly. This failure mode is true for many conditions, not exclusively for the main PS board PE0071. It could be caused by many things, LOW B, SEINE, AV_TERM, LCD, PROTECT, etc.

Specifically for PE0071+12VDC circuit failure, which is the most common , listen for the LINE relays SR80, SR81 coming online. If several (3) or more clicks are present when applying power to the TV set then suspect the +12, 20, +32 VDC inverter is faulty.

As a quick check, you can disconnect P807B. If the relays cycle every 1-2 seconds then is most definitely the +12VDC inverter. Check for voltage level at optocoupler Q881 pin 4 and this should not be cycling. This point is the VCC for the oscillator. Repair or replace board 75002913 as necessary.

TROUBLESHOOTING: (this is my own, not the OEM !, try at your own risk!)

1. Check for LINE1 input voltage level at inverter on sheet [4].
2. Check for LINE2 input voltage level at inverter on sheet [3].
3. Check for STBY +5VDC & +25 VDC ( observe correct GND REF) page [4]of PE0071 POWER
4. Check for +22 VDC out of regulator on page [3] out of Q822 Emitter
5. Check P809B connector for :

• P809B (12) POWER = 3.00 VDC (+/-0.2)
• P809B (11) POWER_SIG = 0.00 VDC (HIGH to Power on TV)
• P809B (10) PROTECT = 0.00 VDC

• P809B (9) ACDETECT = 3.00 VDC (+/-0.2)

1. Check for PFC_OUT = 368-371 VDC
2. Check for +12, +20 & +32 VDC inverter page [5] of schematic manual.
   

For +12 VDC Inverter, suspect components:

Q880 STR-W6765 PSR (works really hot!!)
C888-C890
D884A and related switching circuit components.

Good luck,

mrwindex

Yes this is a good list of the voltages to be expected from a newer power supply on just the main header