Insignia NS-37D20SNA14 power supply buzzing

[RRice25541]

Hi everyone,
I'm working on an Insignia NS-37D20SNA14,

original issue was it would come on play for a while then turn itself off,
It could be turned back on when it auto shutoff but would only run for about 30 sec to 1 minute or so before shutting off again..

I found bad connections on the led strip junctions, so i soldered wires across each strip since flexing the connections or swapping the strips around didn't help anything..
The TV seems to stay on longer now but the power board is making a really bad buzzing noise or whine.. this buzzing was there before i started disassembly tho

it's not that noticeable with the back panel installed on it at first but it gets louder the longer the set runs,,
if i disconnect the led plug the buzzing stops..
I've checked the ESR on all electrolytic capacitors and pulled all safety caps and checked them on the cap check function of my DMM, all seem to be fine.

I'm wondering if one might be breaking down when current is flowing thru it or something,,
Has anyone else run across this issue and found the solution for it?

[RRice25541]

Re: Insignia NS-37D20SNA14 power supply buzzing

Update:
I have noticed a very odd issue..
if i turn the backlight brightness all the way down to zero the brightness doe not change until i turn the unit off and then back on, (buzzing noise remains the same)
If i crank it all the way to 100% again the brightness doesn't change until i turn the unit off and then back on again(buzzing noise has decreased 90% less now)

Think the problem may be the MP4012 LED Controller?

[R_J]

Re: Insignia NS-37D20SNA14 power supply buzzing

I would replace C510 & C11 and see if it makes a difference. Is this a high pitch squeal noise? Where is the noise coming from (I mean which component IE transformer)? I doubt it's an led controller ic problem.

[RRice25541]

Re: Insignia NS-37D20SNA14 power supply buzzing

kinda hard to tell but it sounds like it's coming from V601
which is also seems to be getting extremely hot

[R_J]

Re: Insignia NS-37D20SNA14 power supply buzzing

What is the voltage on the anode of D603.

[RRice25541]

Re: Insignia NS-37D20SNA14 power supply buzzing

I'll get that voltage for ya tomorrow

[R_J]

Re: Insignia NS-37D20SNA14 power supply buzzing

Looks like it should be around +55vdc, I would also check the voltage on the cathode of D603, this is the boosted voltage for the led's

[RRice25541]

Re: Insignia NS-37D20SNA14 power supply buzzing

ok with the BL at 100% there's 119VDC across the BL strips connector..
and with the BL at 0% there's 63VDC.
There's 124VDC on the Cathode of D603 referenced to chassis ground
I need to clarify something.
I'm not saying the BL is Not working they are working just fine.. but the change from 0% to 100% or vise versa does not take effect until the set is turned off and turned back on..
so normally when you change a setting you visually see the BL go dimmer or brighter depending on which way your going,, this unit does not show any change until it restarted

[R_J]

Re: Insignia NS-37D20SNA14 power supply buzzing

I was just thinking the voltage could be wrong and causing the buzzing, So does the voltage change on the PWM pin when you vary the backlight setting? (this would be best checked with a scope) If the voltage does'nt change when you vary the backlight setting, but the voltage is different when you turn the tv off then back on, it could be a main board issue.

[RRice25541]

Re: Insignia NS-37D20SNA14 power supply buzzing

My isolation transformer toasted a few weeks ago, i really don't feel comfortable hooking my scope to it,,
I suppose i could use a ground lift on the scope and maybe get by checking it since it's on the secondary side of the power supply ..
I'll check the voltage first and see if it's doing anything and get back to you about the signal from a scope ,,
main board processor maybe, since the PWM signal comes directly from there

[R_J]

Re: Insignia NS-37D20SNA14 power supply buzzing

You should be ok connecting the scope because you are on the cold side of the power supply. You can check the ac voltage between scope ground and tv chassis, you will likely read some ac voltage but it will have 0 current.
It seems like the pwm level data is changing and the level is being stored in eeprom, but it is not changing the pwm signal to the PS, but when it is turned off and on the stored data is read and the pwm level is sent to the PS board.

[RRice25541]

Re: Insignia NS-37D20SNA14 power supply buzzing

ok checked the voltage on the PWM pin as i went from 0% BL to 100% BL.
with the tv on and the BL at 0% the voltage on the PWM pin was .47vDC
when i ramped the BL up to full without turning the tv off the voltage stayed at .47VDC
when i turned the tv off and back on the voltage was 3.67vDC
This would seem to point to the problem more likely on the MB rather than on the PS tho

[R_J]

Re: Insignia NS-37D20SNA14 power supply buzzing

Thats what it seems like, that voltage should change when the BL level is changed, If it was working correctly you would see it change from .5 ~ 4 volts when you changed it in the menu.
It might be an eeprom issue? you can try freezing it to see if it makes a difference
If you have a programmer, you could remove the eeprom, copy the data and program a new ic, that might be all that is needed.

[RRice25541]

Re: Insignia NS-37D20SNA14 power supply buzzing

I do have a programmer, so i'll try the eeprom first..But
does anyone have a dump of the eeprom just in case the code itself is corrupted..
I searched the sites eeproms data forum and couldn't find anything for this model

[R_J]

Re: Insignia NS-37D20SNA14 power supply buzzing

I do see shopjimmy has an eeprom for $15.00 so if all else fails...
The data itself may not be corrupt, but the ic itself has an issue with read/write. It should'nt be an issue because the micro should output the pwm signal to the power supply, but who knows how it actually does this.

[RRice25541]

Re: Insignia NS-37D20SNA14 power supply buzzing

update:
went to the menu and changed the picture setting from standard, vivid etc.etc.. and the changes take effect instantly, even the BL brightness..
So now I'm even more confused

[R_J]

Re: Insignia NS-37D20SNA14 power supply buzzing

Likely an error that effects the way the program works, When you try adjusting the BL, it is not sending the pwm information out of the micro, but when you retrieve a stored value (vivid, standard etc.) it outputs the pwm stored value without a problem. it only takes one bit of data to be corrupt to effect the operation, everything else is uneffected.