LG47LC7DF power supply issue- pics and some voltages

[links56]

Hey everyone, I'm trying to fix the power supply board on my lg47lc7df tv.

Problem:
No power
No power light

Things I've done:
replaced the 9 capacitors that usually go bad.

Things I've checked:
both fuses are good
I get a reading of 250 vac at fuse F 700
Both filter caps have 175vdc.
Connector P203 has twelve pins reads as follows
Pin1-.714v
pin2-.714v
pin3-none
pin4-none
pin5-.090v
pin6-.090v
pin7 Thru pin12 have no reading

I'm posting pictures of the top of the board, and the heat shield, also another picture of the bottom half of the board. I don't have pictures of the bottom yet but there are no burned spots or anything.




Let me know if I have left out any needed information or any other questions that will help in diagnosing what's wrong. Thanks.

[CapLeaker]

Re: LG47LC7DF power supply issue- pics and some voltages

You need to find the 5v standby voltage. Since there isn't any light on, I don't think it is present. You need to find a schematic and work on getting that standby voltage back. That standby voltage is there all the time, tv on or off.

[links56]

Re: LG47LC7DF power supply issue- pics and some voltages

Where should I check for 5v? Is there a spot with the schematics I could get it from? Thanks.

[CapLeaker]

Re: LG47LC7DF power supply issue- pics and some voltages

It must be on the ribbon power cable that goes from your power supply to the main board. As GND for your measurements use chassis ground. On the first pic of the power supply board are a bunch of ribbon cables at the top right... one of them goes to the main board. Some sets have a 3.3V standby line. Without that voltage being there, nothing goes.

[nomoresonys]

Re: LG47LC7DF power supply issue- pics and some voltages

what you got there, plasma, lcd, led?

[budm]

Re: LG47LC7DF power supply issue- pics and some voltages

The 3 white connectors with multiple wires have label for each pin to tell us what they are.
Take the Voltage readings and report the reading of each pin with the name of the pin so we can tell what voltages you are getting on each pin.
http://www.shopjimmy.com/lg-eay36781...upply-unit.htm

[links56]

Re: LG47LC7DF power supply issue- pics and some voltages

It's LCD I believe. Starting with the top connector P201

PIN1-ACD- 5.06v
Pin2-on/off-0.0v
Pin3-st5v-5.06v
pin4-GND-0.0v
Pin5-in ctrl-0.0v
Pin6-err-0.0v
pin7-burst dim-0.0
Pin8-st5v-5.06v
Pin9-GND-0.0v
pin10-adim-0.0v
Pin11-6.5v-0.0v
pin12-GND-0.0v
Pin13-3.4v-0.0v

Connector P202 has no voltage on any of the pins

Connector P203

Pin1-3.4v-.714v
pin2-3.4v-.714v
pin3-GND-0.0v
Pin4-GND-0.0v
pin5-6.5v-.090v
Pin6-6.5v-.090v
pin7-GND-0.0v
Pin8-GND-0.0v
pin9-12v-0.0v
Pin10-12v-0.0v
pin11-GND-0.0v
Pin12-GND-0.0v

Hope this helps.thanks.

[CapLeaker]

Re: LG47LC7DF power supply issue- pics and some voltages

So far this means that the standby voltage is actually available on the power supply and the problem is on the main board. You can see if there are any fuses on the main board, as it appears to be dead as a nit. You also can check if you get any shorts on the main board connector P201 pins from any power to GND.

The power flow works like this: STBY voltage is generated all the time on the power supply and goes to the main board. When you press the power button on the TV, the main board sends that STBY voltage back to the power supply and turns on all the rest of it, powering up the TV.
To check out the power supply, you can unplug the mainboard from the power supply, force the power supply and the backlight on using jumpers and check all voltages generated on the power supply.

[links56]

Re: LG47LC7DF power supply issue- pics and some voltages

The main board is the other circuit board in the center of the tv? I'll take the heat shield off and see what it looks like.

[budm]

Re: LG47LC7DF power supply issue- pics and some voltages

Connector P202 has no voltage on any of the pins
I will need the name of those pins also since P201, 202 do not have PS_ON pin.
So right now the main board is not sending the PS_ON to turn on the power supply.
We can force on the power supply using PS_ON pin.

[links56]

Re: LG47LC7DF power supply issue- pics and some voltages

Looks like P202 is :
Pin1-19v?
pin2-19v?
pin3-gnd
pin4-gnd
Pin5-6.5v
pin6-gnd
pin7-3.4v
pin8-gnd
pin9-12v
pin10-gnd


Connector P201 has pin 2 listed as on/off.

[CapLeaker]

Re: LG47LC7DF power supply issue- pics and some voltages

Can you make pic of the top right corner of the power supply with the 3 connectors unplugged, so we can see the pinout? Also maybe the main board and the board numbers of both boards.

[links56]

Re: LG47LC7DF power supply issue- pics and some voltages

Here ya go.

[budm]

Re: LG47LC7DF power supply issue- pics and some voltages

OK, I think I figure out the pin names:
Pin2-on/off-0.0v: This one is the PS_ON pin, >2.5VDC from main board = ON. At first I thought it is the ON/OFF control pin for the Inverter on/off until I saw the pictures on post 13. Right now the main board is not sending the ON (>2.5VDC) command to turn on the rest of the power supply.

Pin5-in ctrl-0.0v: This is the one that threw me off, you did not put down as INV CTRL as shown in your pictures in post 13. This is the inverter ON/OFF control. Right now the main board is not sending the on command either.

And then this pin that you report as "Pin13-3.4v-0.0v" but it is labeled with 3.4V ON, which I am not sure what that means yet. This one it may have to be present right now like the ST5V.
May have to get service manual for this one, more thinking for me to do.

[links56]

Re: LG47LC7DF power supply issue- pics and some voltages

Sorry about that, the auto correct kept changing what I was typing. Anyways I'm glad the picture helped clear that up. I appreciate you guys helping me.

[budm]

Re: LG47LC7DF power supply issue- pics and some voltages

Can I see the whole back side of the TV so I can see how all the boards are connected together?

[links56]

Re: LG47LC7DF power supply issue- pics and some voltages

Here ya go

[budm]

Re: LG47LC7DF power supply issue- pics and some voltages

Service manual:

So the 3.4V is not on until PS_ON is present.

[links56]

Re: LG47LC7DF power supply issue- pics and some voltages

How would I go about forcing the power supply to start? Apply 5v to the on/off pin? Just want to make sure the power supply is working. Thanks.

[budm]

Re: LG47LC7DF power supply issue- pics and some voltages

Use 100~1K 1/4W resistor between the 5VSTBY and the PS_ON on the power supply board pin, but you MUST remove the wire going back to the main board first, we do not want to backfeed the force on Voltage back to the main board.