LG 65UH5500 Dead

[Diah]

Re: LG 65UH5500 Dead

disconnect the LED driver converter voltes board from power supply and read your voltage of 13 and 80

[Diah]

Re: LG 65UH5500 Dead

if there no change. i advice you to solder out the both transformer near the R you replaced it and check them, they may have bad inside pin connection .. i faced this under other platform

[hbdeals]

Re: LG 65UH5500 Dead

disconnect the LED driver converter voltes board from power supply and read your voltage of 13 and 80

No change 45v and 8V.

The 13 volt rail does pulse from 7 to 8 volts as it "tics".

[R_J]

Re: LG 65UH5500 Dead

What is the voltage across C48, that voltage comes from the circuit that had the open resistor
Then, using hot ground (TP21) check the voltage on the opto (ic1) pins 3 & 4 (or zd2)

Voltage on C48=
Voltage on ZD2 anode=
voltage on ZD2 cathode=
RF1 was open, did you check r39 (0Ω). R38 (51Ω), R10 (51Ω) and all 5 diodes

I know no one wants to believe me but this power supply can operate in standby (burst mode)

[hbdeals]

Re: LG 65UH5500 Dead

What is the voltage across C48, that voltage comes from the circuit that had the open resistor
Then, using hot ground (TP21) check the voltage on the opto (ic1) pins 3 & 4 (or zd2)

Voltage on C48=
Voltage on ZD2 anode=
voltage on ZD2 cathode=
I know no one wants to believe me but this power supply can operate in standby (burst mode)

Voltage on C48= pulses between 15 and 19.6 volts
Voltage on ZD2 anode= 0 volts
Voltage on ZD2 cathode= pulses to 2.5 volts

[R_J]

Re: LG 65UH5500 Dead

Check the voltage across C56, then using hot ground check the voltage on D2 cathode, then ZD3 cathode

check r39 (0Ω). R38 (51Ω), R10 (51Ω)
That voltage on C48 may be coming from the ic's startup cell

When U1 starts, the internal startup cell will produce around 20v on pin 6 (SUPIC), this voltage needs to be sustained from an aux source, In this case that is the VCC supply of T1, Pins 5&6 diodes D4,12,18,19, charging C56. That voltage goes through diode D2, R38, clamped by ZD3 and through R10 to U1 pin6

[hbdeals]

Re: LG 65UH5500 Dead

Voltage across C56= 14.8 volts

D2 cathode= 19.6 volts

ZD3 cathode= 19.6 volts

R39 = 0Ω

R38 = 48Ω

R10 = 48Ω

[hbdeals]

Re: LG 65UH5500 Dead

Which side of ZD3 is supposed to be the cathode. It don't have a stripe.

[R_J]

Re: LG 65UH5500 Dead

zd3 cathode is connected to R10. But I can see there is not enough voltage produced on C56.
That 19.6 is coming from U1 and not being produced by T1 VCC winding, check that the winding pin 5~6 is not open.


This could just be because the power supply IS in standby.
Check the voltage (cold side) on IC1 pin 1 and pin 2 , pin 1 is likely close to 8 volts (comes from 13v supply) pin 2 should be less, Check the voltage across pins 1 & 2, if it is 0 volts the led in the opto is not lit.
Find Q1 and short the collector to ground (C is connected to R57) that should turn on ic1

[hbdeals]

Re: LG 65UH5500 Dead

ZD3 cathode is for sure 19.6v

T1 VCC winding 5 to 6 = 0Ω

IC1 Pin 1 = 6.7v
Pin 2 = 5.7v
Across Pins 1 and 2 = .98v (1volt)

[Diah]

Re: LG 65UH5500 Dead

No change 45v and 8V.

The 13 volt rail does pulse from 7 to 8 volts as it "tics".

okay. put the socket back. and just disconnect the LED back light socket from driver board and check you still have the tics ?

[hbdeals]

Re: LG 65UH5500 Dead

okay. put the socket back. and just disconnect the LED back light socket from driver board and check you still have the tics ?

It tics no matter what's connected. I think this TV was a clock in a previous life.

[Diah]

Re: LG 65UH5500 Dead

may be..LOL or yours hair dryer u used before was soldering hot air gun..LOL spare time and replace this boards but be alarm that you will just go back to first point to read 80 13 volts only

[Diah]

Re: LG 65UH5500 Dead

can we see you DM you used measuring the 80 Volts and 13.. where you put the probe and on which setting your DM

[hbdeals]

Re: LG 65UH5500 Dead

may be..LOL or yours hair dryer u used before was soldering hot air gun..LOL spare time and replace this boards but be alarm that you will just go back to first point to read 80 13 volts only

At least then, it didn't tic. I'm using a good digital meter.

[hbdeals]

Re: LG 65UH5500 Dead

Find Q1 and short the collector to ground (C is connected to R57) that should turn on ic1

I did that, and get these voltages now.

IC1 Pin 1 = 8.2v
Pin 2 = 7.5v
Across Pins 1 and 2 = pulses to 1.5v

[R_J]

Re: LG 65UH5500 Dead

So with Q1 collector connected to ground, you had 1.5v across the opto pins 1&2 did the power supply give you 13 & 80volts? if not we can confirm that the opto is working by checking the:
Voltage on ZD2 anode=
Voltage on ZD2 cathode=
with 1.7 volts across pins 1 & 2, the voltage on ZD2 should be very close to the same on anode & cathode.

Do you ever get the full 13 & 80 volts like you did before?

[hbdeals]

Re: LG 65UH5500 Dead

Voltage across ZD2 starts out at 3.8 volts, then with each (tic) it drops in voltage until it reaches 2.2 volts and then recycles at 3.8 volts.


Voltage on ZD2 anode= 0 volts (at times it hit .5 volts maybe) strange

Voltage on ZD2 cathode= 2.5 to 3.7 and anywhere in between on the (tics)


80v and 13v are still 45v and 8V

[R_J]

Re: LG 65UH5500 Dead

so when you have 1.7 volts across pins 1 & 2 of the optocoupler (led side), the photo transistor side (pins 3 & 4) should be conducting and close to the same voltage on each pin so the same voltage should be on both pins of the ZD2 diode.
You could have a bad optocoupler. Whats the number on it?
You could monitor either 13v or 80v supply line and short pins 3 & 4 of the optocoupler, if the opto is at fault the voltage should come up to or slightly above spec.

[hbdeals]

Re: LG 65UH5500 Dead

I'll see if I have any spares.