LG 32LH500B - No power, no standby

[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

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

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

Check E-B and E-C junction Voltages of Q0D1(2A).
Z0D6 soldering does not look very good.
Update Q0D1 is PNP so R2D9 connected to the Emitter of Q0D1 makes sense.
Q0D1 has to be off for the BP pin Voltage to rise to 5.7V

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?

[budm]

Re: LG 32LH500B - No power, no standby

All 3 meter out to 470k almost on the button

Check E-B and E-C junction Voltages of Q0D1(2A).
Z0D6 soldering does not look very good.
Update Q0D1 is PNP so R2D9 connected to the Emitter of Q0D1 makes sense.
Q0D1 has to be off for the BP pin Voltage to rise to 5.7V

[JeffJ]

Re: LG 32LH500B - No power, no standby

I update my post 35, check those 474 resistors.

All 3 meter out to 470k almost on the button

But what you said makes sense and its got to be something in this areas still. because with R2D9 in place BP is low (2.7V) and also the VDC across C0D1, COD4 and the D pin on the LSK677K is all 154.7V. with R2D9 removed across C0D1, COD4 and the D pin on the LSK677K is 160.7VCD which is proper, so something is pulling it down.

[budm]

Re: LG 32LH500B - No power, no standby

I update my post 35, check those 474 resistors.

[JeffJ]

Re: LG 32LH500B - No power, no standby

Also R0D6 goes to the Emitter of Q0D1 which my research suggests is a MMBT3906 (bottom right pin of Q0D1 in attached)

[budm]

Re: LG 32LH500B - No power, no standby

https://www.badcaps.net/forum/attach...5&d=1597280341
Ah, I did not see that section before, it looks to be for either LOW AC (Brow out) protection circuit or Over Voltage protection, more likely to be for Brown out protection, I suspect those high resistance resistors (marked as 474, connected in series) have drifted into higher value and cause fault brownout shutdown thinking that In coming AC is low when it is rally not.
When AC Voltage is low, the regulated power supply will draw more incoming current to maintain the same power output of the power supply.
I think we found the cause of the problem. I wish I see the R2D9 and that detection circuit earlier.
They use BP pin for shutdown in case of Brownout, since the Transistor connected to R2D9 is not active when no power applied to the board, the resistance reading on BP will be high, but when Transistor is turned on (Brown out) when power up the board, the BP is pulled down through R2D9 to keep BP pin Voltage low.

[JeffJ]

Re: LG 32LH500B - No power, no standby

At least we are getting close, it looks like they add something to control the BP pin via R2D9, I am learning too about this IC, this is the first time I deal with this IC P/N.

So if you see the attached that circuit that R2D9 leads to exits through the diode with the white glue on it through the board aboard and goes to the Anode of D0D1 in the Rectification circuit, the top most diode in the rectification diode array thats closest to C0D1 450V cap.

[budm]

Re: LG 32LH500B - No power, no standby

Ok makes sense, thanks for sticking with this, with me. i'm learning a fair bit. I really appreciate you taking the time.

Replacing R0D9 might have ot wait until tomorrow i dont know if i have a 3k resistor, and the other one went off into the ether of my office floor, never to be found again it seems.

I will work on figuring out where R2D9 goes so far I've traced it through the board and then back to the top where it goes on a trace under C0D4 450V 68uf capacitor. It seems to come out on the top of the board on the bottom side of C0D1 to R0D6.

See attached.

At least we are getting close, it looks like they add something to control the BP pin via R2D9, I am learning too about this IC, this is the first time I deal with this IC P/N.

[JeffJ]

Re: LG 32LH500B - No power, no standby

R0D9 (302 = 3K Ohms) looks to be the same function as R9 of the application circuit.
R2D9 (470 = 47 Ohms) I cannot tell where it goes to, I can see that one end is connected BP pin.
I would put the ZENER and R0D9 back in place and see if it still running, right now the BP 5.7V is supplying by the BP not from AUX winding.
I think R2D9 is connected to something on the other end and not allowing the BP to go up.

Ok makes sense, thanks for sticking with this, with me. i'm learning a fair bit. I really appreciate you taking the time.

Replacing R0D9 might have ot wait until tomorrow i dont know if i have a 3k resistor, and the other one went off into the ether of my office floor, never to be found again it seems.

I will work on figuring out where R2D9 goes so far I've traced it through the board and then back to the top where it goes on a trace under C0D4 450V 68uf capacitor. It seems to come out on the top of the board on the bottom side of C0D1 to R0D6.

See attached.

[budm]

Re: LG 32LH500B - No power, no standby

R0D9 (302 = 3K Ohms) looks to be the same function as R9 of the application circuit.
R2D9 (470 = 47 Ohms) I cannot tell where it goes to, I can see that one end is connected BP pin.
I would put the ZENER and R0D9 back in place and see if it still running, right now the BP 5.7V is supplying by the BP not from AUX winding.
I think R2D9 is connected to something on the other end and not allowing the BP to go up.
Per spec sheet, BP pin can source current up to 8mA, that means it can maintain 5.7V with load resistance as low as 5.75V/8.2mA = 700 Ohms and still to maintain 5.7V.
I think R2D9 (47 Ohms) is the key.

[JeffJ]

Re: LG 32LH500B - No power, no standby

OK, I need to look at the pictures to see what and how those resistors are connected.

DOnt know if you caught my edit on the previous post. Also with R2D9, R0D9 and Z0D5 removed BP to S is 68K now.

[budm]

Re: LG 32LH500B - No power, no standby

Removed R2D9 Z0D5 and R0D9 and now BP is 5.7V

and yes their is a way i can do that, I dropped RoD9 on my hardwood floor, and im cursing my self and any one who will listen right now. Not to hard to find another 3kohm resistor though.

OK, I need to look at the pictures to see what and how those resistors are connected.

[JeffJ]

Re: LG 32LH500B - No power, no standby

OK, I need to do more thinking and reading the spec sheet.
BTW is there any way you can have the Volt meter connected between BP pin and GND so you can monitor the Voltage when you first apply the power to the board?

Yes their is a way i can do that, I dropped R0D9 on my hardwood floor, and im cursing my self and any one who will listen right now. Not to hard to find another 3kohm resistor though.

Removed R2D9 Z0D5 and R0D9 and now BP is 5.7V All 3 seem to test ok (resistors correct values) out of circuit. I removed Z0D5 first, tested, no luck, then R0D9, tested, no luck. then R2D9, Tested saw i fgot 5.7VDC on BP.

Oh and here is the kicker.

Tv powers on and works with the above two resistors and diode removed..... I am well i dont know what to say now.

[budm]

Re: LG 32LH500B - No power, no standby

SO ive removed Z0D5 and it test fine out of circuit, still get a reading both ways on tis pads. removed R0D9, still get a reading both ways. BP is still at 2.7V so im missing something else in the bp circuit.

I'll keep digging, welcome to ideas.

OK, I need to do more thinking and reading the spec sheet.
BTW is there any way you can have the Volt meter connected between BP pin and GND so you can monitor the Voltage when you first apply the power to the board?
You should also check the Voltages on PD, CP, and FB pins for the records then I will look at the spec sheet as to what to be expected on those pins.

[JeffJ]

Re: LG 32LH500B - No power, no standby

SO ive removed Z0D5 and it test fine out of circuit, still get a reading both ways on tis pads. removed R0D9, still get a reading both ways. BP is still at 2.7V so im missing something else in the bp circuit.

I'll keep digging, welcome to ideas.

[budm]

Re: LG 32LH500B - No power, no standby

ZOD5 is the added on protection, it is not used in the application circuits as shown in the spec sheet so you can remove it and the circuit should still function without it..
This is getting to be really interesting since the circuit does not have much at all and the circuit they are using is pretty close to the application circuit, most low cost TV will basically copy the application circuits so they do not have to start from scratch and cost them money.

[JeffJ]

Re: LG 32LH500B - No power, no standby

So the resistance reading of that Zener should be about 68K then, correct?
ZOD5 looks to be for protection on the BP pin in case the internal Voltage regulator shorted of have high leakage which will dump high Voltage from D pin to BP pin.
I see page 13 of the spec sheet for the BP shutdown threshold current of 8.2ma so if the over current occur it will go into shutdown.

BP to S i tested 68K when it waso ut of circuit, when i test it in circuit it just keeps rising and rising to several hundred K. testing across that zeener gives the same results.

Should i remove Z0D5 and test BP to S and see what i get then. and also test it out of circuit?