LG 65UH5500 Dead

[hbdeals]

It does does nothing, no power light.

It was getting all of the 80, 13 voltages, but Zero on the standby pin. I warmed the board with a hair dryer for 30 seconds. Now the 80 volts is 45. The 13 volts is 8. Still no life on standby pin.

Disconnecting LED board makes no difference in the voltage readings.

It makes a faint high voltage hissy pulse sound coming from the larger transformers.

Bridge rectifier shows 160 volts output.

360 volts on the 3 long capacitors.

The small yellow LP2 gets 130 degrees F.

The bridge rectifier heat sink gets 125 degrees F.

Everything else is room temperature.

Resistor RF1 reads open, replaced it, no change.

All diodes and fuses check good.

Not sure where or what to check next.

[hbdeals]

Re: LG 65UH5500 Dead

The power board.

[neilc6]

Re: LG 65UH5500 Dead

I would just replace the power supply and buy one from a seller that takes returns on ebay. Schematics would be hard to find and difficult to debug a power supply without one after checking usual suspects (shorted diodes, fets, rectifiers, blown fuses, cold solder joints). That model does suffer from backlight failures as well so I would turn down the backlight level after being repaired.

[hbdeals]

Re: LG 65UH5500 Dead

I would just replace the power supply and buy one from a seller that takes returns on ebay. Schematics would be hard to find and difficult to debug a power supply without one after checking usual suspects (shorted diodes, fets, rectifiers, blown fuses, cold solder joints). That model does suffer from backlight failures as well so I would turn down the backlight level after being repaired.

yep, that's the very reason I'm trying to fix the power board. I'm not too crazy about the other common failures on this one. I've been down the rabbit hole before of replacing board after board and then find out it needs LED strips too.

So anyway, I put the power board in plastic bags and let it sit in the freezer for 30 minutes. hooked it up and the high voltage fizzy pulse got much louder.

Once it went back to room temperature, it's the same faint level it was before.

Guess I need some of that fancy freeze spray.

[R_J]

Re: LG 65UH5500 Dead

The stb pin is the control pin from the main board, it is used to turn the power supply on and off, If you are getting 80 volts and 13 volts, the power supply is working, I suspect your problem is on the mainboard and it is holding the STB line low

[Diah]

Re: LG 65UH5500 Dead

man, are you posting here to trouble shooting TV or Kitchen Oven ? reading temprature or all what did you wrote on first post had nothing to bring any good known member to join and help.

1- start with upload complete photos on whole boards to see how they are connected each other, either the edge BL strip and the connector

2- you have noise at the transformer at hot area... mean you should consider on cold area but you should 100% disconnected main board from PSU and just trace PW ON voltage at PSU side... so you can start repairing

[hbdeals]

Re: LG 65UH5500 Dead

The stb pin is the control pin from the main board, it is used to turn the power supply on and off, If you are getting 80 volts and 13 volts, the power supply is working, I suspect your problem is on the mainboard and it is holding the STB line low

STB is zero volts without any connection to any boards. Getting 45 Volts on the 80 and 8 on the 13.2 pins.

[hbdeals]

Re: LG 65UH5500 Dead

man, are you posting here to trouble shooting TV or Kitchen Oven ? reading temprature or all what did you wrote on first post had nothing to bring any good known member to join and help.

1- start with upload complete photos on whole boards to see how they are connected each other, either the edge BL strip and the connector

2- you have noise at the transformer at hot area... mean you should consider on cold area but you should 100% disconnected main board from PSU and just trace PW ON voltage at PSU side... so you can start repairing

The oven might be in this boards future indeed.

It is disconnected.

I posted a picture of it earlier. It only has one 15 pin connector.

[R_J]

Re: LG 65UH5500 Dead

Well then STB needs to be high to turn on the power supply. What voltage are you expecting on the STB pin?
I suspect the main board takes the 13 volts (standby 8) and regulates it to either 5 or 3.3 volts. the main board will send (3.3/5v) to the STB pin turning the power supply on fully.
with the main disconnected you should be able to apply 3~5 volts to the STB pin and the 80 & 13v will come up full.

[hbdeals]

Re: LG 65UH5500 Dead

Well then STB needs to be high to turn on the power supply. What voltage are you expecting on the STB pin?
I suspect the main board takes the 13 volts (standby 8) and regulates it to either 5 or 3.3 volts. the main board will send (3.3/5v) to the STB pin turning the power supply on fully.
with the main disconnected you should be able to apply 3~5 volts to the STB pin and the 80 & 13v will come up full.

Sounds good. From another post of a person on here, I have deducted that the STB pin should be 3.3 volts. Would a Lithium 3.3 volt battery do it? Thanks

[budm]

Re: LG 65UH5500 Dead

Post #1
"Bridge rectifier shows 160 volts output.
360 volts on the 3 long capacitors."

Sounds like the PFC boosted Voltage is present so PS-ON must be working then. Or may be wrong data if STB stays 0V, or it may be active- low signal.

"Resistor RF1 reads open, replaced it, no change."
Pictures of this RF1? Also provide other pictures as requested by other helpers.

[hbdeals]

Re: LG 65UH5500 Dead

The resistor is circled in the picture. That's the one that tested open.

[hbdeals]

Re: LG 65UH5500 Dead

The yellow LP2 gets warm. 130 degrees via infrared thermometer.

[R_J]

Re: LG 65UH5500 Dead

Coils do get warm , did you try turning on the power supply with the battery?

[budm]

Re: LG 65UH5500 Dead

I am also surprised that you even getting and DC on the output when RF1 (1 Ohm fusible resistor) is open circuit.

[R_J]

Re: LG 65UH5500 Dead

RF1 seems to be a fuse resistor for the circuit that has C56 as the filter and could be the vcc for u1 ? it seems to connect to pin 6 . whatever U1 is

[hbdeals]

Re: LG 65UH5500 Dead

Coils do get warm , did you try turning on the power supply with the battery?

Not yet, not sure how to hook a battery to it. Negative to chassis, positive to pin?

[hbdeals]

Re: LG 65UH5500 Dead

Coils do get warm , did you try turning on the power supply with the battery?

RF1 seems to be a fuse resistor for the circuit that has C56 as the filter and could be the vcc for u1 ? it seems to connect to pin 6 . whatever U1 is

That thing is a fuse? Dang well the resistor I replaced it with is a 1 ohm resistor. C56 wasn't charging with the old resistor fuse. It charges up now with a good snap if I short the cap out with a screwdriver.

[R_J]

Re: LG 65UH5500 Dead

It can be called a fusable resistor or it could just be a 1Ω flame proof resistor, it is there to protect the power supply if something shorts like the main ic, DON'T short capacitors like that, the high current spark can cause damage elsewhere in the circuit, like the main u1 ic. Always discharge a cap with a proper resistor
And to turn on the power supply with the 3v battery, it is negative to ground pin, positive to STB pin (main board plug disconnected)

[hbdeals]

Re: LG 65UH5500 Dead

It can be called a fusable resistor or it could just be a 1Ω flame proof resistor, it is there to protect the power supply if something shorts like the main ic, DON'T short capacitors like that, the high current spark can cause damage elsewhere in the circuit, like the main u1 ic. Always discharge a cap with a proper resistor
And to turn on the power supply with the 3v battery, it is negative to ground pin, positive to STB pin (main board plug disconnected)

I'm aware of the "rules", and I fully understand what you mean. I have fixed many tv's with these rudimentary methods, but this one is one of those that's beyond my backwoods electronic skills. It's ok if this one don't pan out, I have a pile of them in line for more torture... haha

I will try to be more civil with this one until there is a conclusion. I promise that there will be an ending to this story, good or bad. Thanks for the help.