Insignia NS-39L700A12 backlight transformer high pitched wine

[R_J]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

The backlights flicker, the inductor noise changes when I push on it

There could be a fault with the led's causing the problem, carefully remove the lcd panel & diffusers and see if there are some bad led's.

[MikeRWK]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

I've decided to scrap the tv it was free anyways.

[MikeRWK]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

L601 is NOT a transformer, it is just a coil (inductor) In this case it is used to boost the led voltage, Is the base supply voltage ok and clean? If the supply is not filtered properly, there can be a beat frequency between the main supply transformer frequency and the led driver frequency.
Or it could just be due to loose windings or cracked core in the coil. Are the backlights ok and does the whine change with if you change the backlight level?

The backlights flicker, the inductor noise changes when I push on it

[R_J]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

L601 is NOT a transformer, it is just a coil (inductor) In this case it is used to boost the led voltage, Is the base supply voltage ok and clean? If the supply is not filtered properly, there can be a beat frequency between the main supply transformer frequency and the led driver frequency.
Or it could just be due to loose windings or cracked core in the coil. Are the backlights ok and does the whine change with if you change the backlight level?

[MikeRWK]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

I replaced all the electrolytic caps with known good ones and it's still got the high pitched noise coming from the transformer. What causes transformer whine?

[R_J]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

18 volts is fine for the main & pfc ic's The emitter voltage will be higher in standby because the transistor is turned off. So is the vcc voltage in standby 21.5v or is iI changing? In standby, N503 is in burst mode so the vcc voltage could be changing, or the capacitor for that voltage is bad. The standby ic also uses this voltage but only requires it to be around 15 volts (stop voltage is 8.1v) in standby

[MikeRWK]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

Should the voltage on the emitter fluctuate like this with the tv off? https://streamable.com/x4o0z1

[MikeRWK]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

If the 18v is stable then it should be ok, if it is slow to build up to 18v then there is a problem. To be sure of the voltage I would need the part numbers on N504 & N501

Here are pictures of N504 and N501. I forgot to mention the Emitter voltage at standby is 21.5v

[R_J]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

If the 18v is stable then it should be ok, if it is slow to build up to 18v then there is a problem. To be sure of the voltage I would need the part numbers on N504 & N501

[MikeRWK]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

I asked for the emitter & collector voltages to see if the ic's had the proper vcc, Since you did'nt post it here, I suggest you look up the ic's datasheet and see if they are correct.

I meant to post pics, here they are.

[R_J]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

I checked the voltages on the transistor the pic with the meter illuminated is Emitter and the other pic is Collector voltage. I replaced all the capacitors besides 4 that I don't have at the moment and it seems more likely to power up when its first plugged in but its still the same.

It's occurred to me I'm going to need a capacitance meter to make things easier in the future.

I asked for the emitter & collector voltages to see if the ic's had the proper vcc, Since you did'nt post it here, I suggest you look up the ic's datasheet and see if they are correct.

[MikeRWK]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

Ebay is loaded with them, about 7-15 bucks, on a slow boat from china, can get a closer shipper but it's about double the price.

I usually pull them from working tvs with broken screens, which is why I really need to buy a capacitance meter.

[nomoresonys]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

I checked the voltages on the transistor the pic with the meter illuminated is Emitter and the other pic is Collector voltage. I replaced all the capacitors besides 4 that I don't have at the moment and it seems more likely to power up when its first plugged in but its still the same.

It's occurred to me I'm going to need a capacitance meter to make things easier in the future.

Ebay is loaded with them, about 7-15 bucks, on a slow boat from china, can get a closer shipper but it's about double the price.

[MikeRWK]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

If the transistor, which I am guessing is V503 was open, the tv would not operate at all. It is best to check the emitter and collector voltage when the tv is turned ON, Using HOT GROUND. this will give tell you if you have proper vcc voltage for the primary ic's to operate.
The main filter voltage going from 160vdc to 200vdc indicates the pfc circuit is working. I would replace those small electrolytics in the primary circuits, they can go weak and cause this type of problem.

I checked the voltages on the transistor the pic with the meter illuminated is Emitter and the other pic is Collector voltage. I replaced all the capacitors besides 4 that I don't have at the moment and it seems more likely to power up when its first plugged in but its still the same.

It's occurred to me I'm going to need a capacitance meter to make things easier in the future.

[R_J]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

By dead I meant open, I tested it according to this video https://youtu.be/GFitoQSbLvA?t=302 , while I don't understand the language I see what he's doing.

If the transistor, which I am guessing is V503 was open, the tv would not operate at all. It is best to check the emitter and collector voltage when the tv is turned ON, Using HOT GROUND. this will give tell you if you have proper vcc voltage for the primary ic's to operate.
The main filter voltage going from 160vdc to 200vdc indicates the pfc circuit is working. I would replace those small electrolytics in the primary circuits, they can go weak and cause this type of problem.

[MikeRWK]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

They don't look to be doming but I'll swap them out.

[nomoresonys]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

Agree, either there's some doming or it's one hellofa optical illusion.

[dick_barton]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

There look like there are at least 2 bad caps, C556 & C554, (or it is just the angle of the picture) start by replacing them. One is for the standby +5 the other is for the +12v. see if that helps.

As R_J says, some of those capacitors do look as though the tops are doming. Are you certain they are not??

[MikeRWK]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

Is this V503???? Explain "dead", shorted, open, leaky ? If it is this transistor it is the vcc switch for the main and pfc ic's
Slow turn on is likely due to bad caps, C536 & C531, standby startup cap. & vcc supply cap.
C519 & C520 are vcc & start cap for the main ic N504

Have you checked the voltage across the main filter C517? check it in standby and then again when the tv is turned on. this voltage should be 160vdc in standby and go up to around (200vdc?) when tv is on.

By dead I meant open, I tested it according to this video https://youtu.be/GFitoQSbLvA?t=302 , while I don't understand the language I see what he's doing.

[MikeRWK]

Re: Insignia NS-39L700A12 backlight transformer high pitched wine

Standby is 162-163 and when I try and power it up it goes up to 206 and settles at 199 while hissing. Then it goes crazy and the voltage fluctuates https://streamable.com/wjr9s6 I was pressing the volume buttons in the video.

Also is this resistor supposed to be hot to the touch?