LG 47LH90 No standby voltage

[Wingryder]

Simple enough with a few twists I need some help with.
1. First off when I download the service manual http://www.manualslib.com/manual/987...90.html#manual
, I get the correct tv.. until I get to the schematics. Nothing matches. It has IC's in the 700 mine are 500. Don't understand

2. P.O. told me he took off the back and looked at the caps. check the inverter picture. He more than looked at them. Underneath ok. but still very concerned about this board.

3. Which brings me to the first and real problem. No 5 volts with main board unplugged so I know it is on the ps board. This supply runs the bridge rectifier at 160 volts on standby all the time. Then it jumps to around 380 when powered up.
Ok.. here is where I need help. Since I cannot find a power supply diagram or schematic for this.. I do not recognize the 5 volt supply path from the bridge rectifier to the output connector. . I have 166 volts on the Bridge Rectifier. (power off) and measuring from neg side of large cap (circled on pic) I have 46 volts when measured on both sides of the fuse (also circled).

Don't know if that is way low or ok... and I am stuck at this point.

I can run a multimeter, measure voltages, check diodes, resistors, fuses.
not so sure of myself testing mosfets, regulators and chips but I am learning.

so if you can help me find the missing standby.. I would appreciate it.

[budm]

Re: LG 47LH90 No standby voltage

Can we see the whole back side of the TV so we can see how all the boards are connected together?
Also need straight shot pictures of the whole power supply board top side and the bottom side.

[budm]

Re: LG 47LH90 No standby voltage

IC501 is part of the 5VSTBY SMPS.
What is the P/N of IC501?
There are four small lytics caps in that section, some of them are for startup/running cap for the STBY supply.
Did you also already test the rectifier diodes in the cold side of the STBY power supply?

[Wingryder]

Re: LG 47LH90 No standby voltage

Bud

It is XK942015x04
ICE 3B0365J
G0930L0P

Hard to read hope it's correct. Working on the requested pictures.

[Wingryder]

Re: LG 47LH90 No standby voltage

Here are the requested pic. No sun today so....

[budm]

Re: LG 47LH90 No standby voltage

Here is the spec of the IC ICE3B0365J.
I will have to wait to see the pictures of the whole board to see if there is and fusible resistor for feeding the B+ to that STBY section or not.

[budm]

Re: LG 47LH90 No standby voltage

Check R501 (fusible for b+ feeding the STBY SMPS), R503.
Should be <1 Ohms.
Check the RESISTANCE of Zener DIODE ZD502.
Check the rectifier DIODE D201.
C506 is the startup/running cap.

[Wingryder]

Re: LG 47LH90 No standby voltage

Quote "Did you also already test the rectifier diodes in the cold side of the STBY power supply? there is a Zener right under that IC that looked open until I took it out, then tested ok. I have tested most small diodes and nothing jumped out at me.

[budm]

Re: LG 47LH90 No standby voltage

OK, I read post 1 again:
'3. Which brings me to the first and real problem. No 5 volts with main board unplugged so I know it is on the ps board. This supply runs the bridge rectifier at 160 volts on standby all the time. Then it jumps to around 380 when powered up. ' That does not make sense to me yet because it is telling me that the PFC Voltage booster circuit is working, and for it to work, it get the Voltage to run from the standby power supply section, and the main board has to be getting the STBY Voltage to run to send the PS-ON to turn on the PFC section.
So which pin on the connector you are measuring the 5V?
Can I see closed up pictures of the connector P201?

[budm]

Re: LG 47LH90 No standby voltage

BTW, I need straight shot pictures of the whole board, pictures are still cutout so I cannot trace circuits.

[Wingryder]

Re: LG 47LH90 No standby voltage

R501 2.3 ohms
ZD502 30.k one way and ol the other
D201 seems to climb up to around 1k measuring from middle leg to both sides and about the same reversing leads. I will take it out and recheck it in the morning.. ran out of time today.
Big thanks for your timely help.

[Wingryder]

Re: LG 47LH90 No standby voltage

Bud I do not get the 360 volts mentioned... I was just explaining how it should work.

I get only the 160 standby . Better Pic tomorrow

[Wingryder]

Re: LG 47LH90 No standby voltage

Bud Sorry about the misleading you with the 380 volt comment. I do not have this. I only have the 166 out of the Bridge for standby. Then it drops to 46 at the Fuse.. After that I did not know where to test.
To answer your question about the cold side rectifiers. The Scottky's on the heatsink measure .171 and .343 for the en220a's and the en210a was .171/.425 (both sides)
This was in circuit ... but where they were all pretty much the same I think they are ok.
Here are some more pictures.. hope they will work

thanks again (and enjoy your Christmas this will still be there later)

[budm]

Re: LG 47LH90 No standby voltage

OK, so the fusible resistor is OK which means we do have 160VDC for the IC501 to run.
You can test the power supply board by itself without having other boards connected to it.
We need to check the DCV between the two legs of C506.
The Voltage on that cap must reach 18VDC (per spec sheet page 16) when first the power is applied to the board for the IC to start running.

[Wingryder]

Re: LG 47LH90 No standby voltage

Bud
I see no voltage on 506

[budm]

Re: LG 47LH90 No standby voltage

OK, please check the DCV between GND pin 8 and the Drain pin 8, if you do have 160 VDC between those two pins, then there is problem with charge pump circuit inside the IC that supposes to charge up C506 to 18 VDC.
I do not expect 0 VDC, I would expect to see some Voltage on the cap, otherwise the IC is really dead.

[Wingryder]

Re: LG 47LH90 No standby voltage

Ok some big changes. I would swear I was getting that 46 volts at the fuse with the power switch turned off. I thought this circuit was active just when plugged in. (standby)
Anyway now it is about 3 volts with the switch off and I guess goes to nothing if the caps are fully discharged.
Power switch on and 166 volts on the fuse.. and on the Fuseable resistor R501. I now get about 14 volts across C506.. Still nothing from drain to ground on IC in question.

[budm]

Re: LG 47LH90 No standby voltage

To check if you do have 160vdc on pin 8, you can use the negative leg of the main filter cap as the GND ref point. I want to check it just to be sure that the primary winding of the STBY transformer does not have open connection.
D201 doe snot show as shorted circuit (that is what I was looking for) so I will not worry about that for now. Right now we need to find ouy why we are not getting the VCC 18 to start up the IC.
May be you can try removing the Zener diode (ZD502 which is connected in parallel with C506), or try new start up cap. Most of the time the failure in that startup section is due to leaky cap or Zener on the VCC pin that does not allow the voltage to reach the start up Voltage, but yours is not even show the sign of charging up at all. You can try new IC at this point of the Zener removal or replacing the cap does not work.

[Wingryder]

Re: LG 47LH90 No standby voltage

Bud you are not going to believe this. Put the board back in to take those measurements.. checked them a time or two and looked down and had red standby light. Could not believe it. Shut everything down again and waited a few minutes then hooked main board and inverter board back in. Plugged in in.. standby light was on. Power it up and looks great. Audio is there and picture full of snow which delighted me. (no input yet). Family calls so that's it for tonight at least. Must have a bad joint on that board. It might be hard to find. So far those horrible solder joints on the inverter board are not causing problems. I will do a little hot and cold and see If I can get the standby voltage to fail . Going to let it rest for now.

Thanks so much for your patience and help. I will add a follow up tomorrow. I hope.
Wow.. Merry Christmas to you and yours.

[Wingryder]

Re: LG 47LH90 No standby voltage

Correction I plugged in main board to make it easier to probe connector for 5 volts. That's when I got the standby light for the first time. Now just got to find the broken trace or bad joint. Still pretty stoked.