LG 32LH500B - No power, no standby

[budm]

Re: LG 32LH500B - No power, no standby

Alright, this i will have to do tomorrow I only have a TS100 at home and my air station is at work, and i feel like i should get this back together properly so we can meter Q0D1 out properly to give us answers.


Ill touch up Z0D6 as well

Should i resemble everything or just R2D9?

I do not quite understand what resemble everything is?
English is my second language and I am still learning.

[JeffJ]

Re: LG 32LH500B - No power, no standby

I do not quite understand what resemble everything is?
English is my second language and I am still learning.

I meant Reassemble replace R0D9 R2D9 and Z0D5.

English is my first language, and I am not good at spelling or proof reading it seems lol

[budm]

Re: LG 32LH500B - No power, no standby

You can leave R2D9 out for now since it is for protection not for the circuit to function, every thing else can be put back in place.
More likely that Q0D1 is on right now which it should not be on since AC Voltage is fine..

[JeffJ]

Re: LG 32LH500B - No power, no standby

IT looks like
E-C .36v dc 2.5v ac
B-E .3v dc 2.5v ac

[budm]

Re: LG 32LH500B - No power, no standby

IT looks like
E-C .36v dc 2.5v ac
B-E .3v dc 2.5v ac

That Transistor should not be on right now, it should not be showing E-C of 0.36V
What Voltage do you have on Z0D6?
You should test that Transistor.

[JeffJ]

Re: LG 32LH500B - No power, no standby

That Transistor should not be on right now, it should not be showing E-C of 0.36V
What Voltage do you have on Z0D6?
You should test that Transistor.

Z0D6 the anode goes to the negative terminal of C0D1

across it i get .7 Vac

[budm]

Re: LG 32LH500B - No power, no standby

Is the Collector of QOD1 also connected to the Anode of Z0D6?
What is the DC Voltage on Z0D46?
Negative leg of C0D1/COD4 (connected in parallel) is the hot side circuit Ground.
I am trying to draw up the schematic of this sensing circuit.

[JeffJ]

Re: LG 32LH500B - No power, no standby

Is the Collector of QOD1 also connected to the Anode of Z0D6?
What is the DC Voltage on Z0D46?
Negative leg of C0D1/COD4 (connected in parallel) is the hot side circuit Ground.
I am trying to draw up the schematic of this sensing circuit.

Collector of Q0D1 is attached to the annode of Z0D6 DCV is .54v across Z0D6

[JeffJ]

Re: LG 32LH500B - No power, no standby

Here is another photo to show traces hope it helps

[budm]

Re: LG 32LH500B - No power, no standby

Collector of Q0D1 is attached to the annode of Z0D6 DCV is .54v across Z0D6

That is bad, I expect 6V or more on that ZOD6.
What resistance do you get in both direction of that ZOD6?
It has R0D5 (394) and COD5 connected in parallel with it.

[JeffJ]

Re: LG 32LH500B - No power, no standby

That is bad, I expect 6V or more on that ZOD6.
What resistance do you get in both direction of that ZOD6?
It has R0D5 (394) and COD5 connected in parallel with it.

17K i in one direction on Z0D6 (Positive probe on anode) and 22k in the other (negitive probe on anode)

17k on both R0D5 and COD5.

ZOD6 and Q0D1 were measured with out R2D9 in circuit, just so you know.

[budm]

Re: LG 32LH500B - No power, no standby

17K i in one direction on Z0D6 (Positive probe on anode) and 22k in the other (negitive probe on anode)

17k on both R0D5 and COD5.

ZOD6 and Q0D1 were measured with out R2D9 in circuit, just so you know.

That does not sound right.
Here is the schematic that I reverse engineer based on what I can see in the pictures.
You should verify it if you can.

[JeffJ]

Re: LG 32LH500B - No power, no standby

R0D6 is connected to the emitter of Q0D1 and from R0D6 it goes to R2D9 so they are in series So Q0D1 Emitter -> R0D6 -> R2D9 -> BP

D1D2 you have labeled is actually labeled D1D3 (Markings "M7" on the diode) And its Anode is connected to the Anode of D0D1 in the rectification diodes.

The Main Filter cap - terminal the circuit actually goes to is C0D4 but thats labeling because the filter caps negative sides are tied together.

SO its all basically correct and I do not get 390K across Z0D5 C0D5 and R0D5 Id expect i should so something there is low and its pulling the circuit down. I get 22k Which is super low.

Also i dont have any 3k resistors can i replace R0D9 with a 3.3k one? i assume this should be alright since figure 11 shows R9 for the LNK6777K as 4.7K which i do have as well.

[JeffJ]

Re: LG 32LH500B - No power, no standby

Here is a quick draw up with the corrections i made to yours, feel free to suggest if something is wrong.

Edit: Ive removed ZD06 ans its 22K across it, now 389K across R0D5 and C0D5 as expected. So its safe to say this is the failed part... I have no idea its Value is it safe to leave it out?

[JeffJ]

Re: LG 32LH500B - No power, no standby

Ok sorry for the rapid posting, I replaced R0D9 with a 4.7K SMD because thats what i had and the Diagram for LMK677K suggested this was a valid option.

I removed ZD06 IT was shorted, well it was 22K which was very low.

I put it all back together with out ZD06, everything else is populated on the board as it should be (put R2D9 and R0D9 back on the board)

Now i get 12vdc at the Base of the PNP transistor and BP now reads 7VDC suggesting its no longer running on its internal regulator and is running on the aux winding.

The tv powers up and works perfect now.

SO is it safe to just leave out the Zeener i removed? If not how do we tell the value of what should be there.

I know the back is labled 120v 1.2A but this TV is only pulling 25W according to my battery backup. Just as an observation.

I would call this TV fixed as long as their is no Health/fire hazard leaving it as it is.

[budm]

Re: LG 32LH500B - No power, no standby

So if the BP is 7V then the Zener Didoe has to be higher than 7V to keep the Transistor off and since typical E-B reverse bias Voltage it can handle is about 5V, right now we are at about 5V without Zener in place because you have 12V at the Base, I would suggest 9.1V Zener so the Transistor will not be damaged.
I am glad we finally fix the problem, thanks to your good clear pictures and your knowledge that I did have to do too much to point you to the right direction.
BTW, you should add 'K' to those 470K resistors.
This thread should help other people with the same model in the future as well.

[JeffJ]

Re: LG 32LH500B - No power, no standby

So if the BP is 7V then the Zener Didoe has to be higher than 7V to keep the Transistor off and since typical E-B reverse bias Voltage it can handle is about 5V, right we are at about 5V without Zener in place because you have 12V at the Base, I would suggest 9.1V Zener
I am glad we finally fix the problem, thanks to your good clear pictures and your knowledge that I did have to do too much to point you to the right direction.
BTW, you should add 'K' to those 470K resistors.
This thread should help other people with the same model in the future as well.

Will do, and the effects if i do no replace the Zeener? can it be ran like this until my next digi order?

[budm]

Re: LG 32LH500B - No power, no standby

The Transistor may fail if AC Voltage goes higer since we are at the 5V limit already.

[JeffJ]

Re: LG 32LH500B - No power, no standby

The Transistor may fail if AC Voltage goes higer since we are at the 5V limit already.

Thanks for the help, i have it running right now i suppose i should shut it off until i get the new diode

Attached is the finished schematic with the 470K resistors labeled as such.

[JeffJ]

Re: LG 32LH500B - No power, no standby

So if the BP is 7V then the Zener Didoe has to be higher than 7V to keep the Transistor off and since typical E-B reverse bias Voltage it can handle is about 5V, right now we are at about 5V without Zener in place because you have 12V at the Base, I would suggest 9.1V Zener so the Transistor will not be damaged.
I am glad we finally fix the problem, thanks to your good clear pictures and your knowledge that I did have to do too much to point you to the right direction.
BTW, you should add 'K' to those 470K resistors.
This thread should help other people with the same model in the future as well.

Woudl this be a suitable one?

https://www.digikey.ca/en/products/d...1-GS08/4934142

Edit, I just put fresh batteries in my meter and retested the voltage on BP to be sure, and its consistently 6.4VDC, 12.5VDC on the Base of Q0D1.

Is a 9.1 VZ for D0D6 still acceptable?