Insignia NS-LTDVD26 Video shuts off after 10 minutes

[Mad Capper]

I have acquired a Insignia NS-LTDVD26


It works fine for 10 minutes then the video shuts off, the audio continues to work. Sometimes you can turn the TV off then back on and it will work for another minute maybe two max and then the video shuts off again. Other times after the video goes off then shutting the TV off then right back on I only get audio. Letting it sit for a while before turning it back on will allow it to work again also.

The outputs from the PSU all check out good when the tv is on. After the 10 minutes and video shuts off the all the 24V outputs go to 0 the rest are still good.

I though heat could be an issue so I used an infrared thermometer to take temperatures around the board but mainly on the components attached to the heat sinks. I noticed there was a spot in the middle on the bottom of the right-hand heat sink in the picture that was around 20 degrees warmer than the others.

Under the heat sink in that area is a resistor and a capacitor. On the bottom of the board in that location, IC3, is a 230D6, PWM controller. I put a fan blowing directly at the heat sink and the problem was still occurred. Then I positioned the fan with a shroud blowing directly under the heat sink where the elevated temperature was coming from and then it worked for over an hour.

Attached to that heat sink on the bottom left is a P9NK70ZFP Zener-Protected Power MOSFET. As I tried to specifically target under the heat sink I think the the MOSFET is not the problem, its temperature did not fluctuate very much at all with or without the fan present.

I do not know if this is a red herring or there is another problem. Also I do not know if one of those components is the problem or something else is causing the problem to potentially be exhibited there. Or maybe(probably) I am way off.

Any thoughts that you all may have to rehab this TV are appreciated.

Thank You Kindly

[retiredcaps]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

1) I count 9 electrolytic caps not including the big one. If this were my TV, I would replace them all as they look like Samxon GF series (a known bad series).

2) I also see some solder ring cracks (selldoor is the eagle eyes). I just circled some that were obvious to me, but there may be more. I suggest reflowing/resoldering them with 60/40.

3) You may want to change the main board as well for bad caps, poor soldering, etc.

4) When the 24V goes to 0V, what is the DC voltage on the BKON pin? I'm assuming it is around 3V DC when 24V is present. If BKON is 0 when the voltages disappear, then your problem is on the main board.

[Mad Capper]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

I reflowed the joints you pointed out and a few others that also looked suspect. The problem persisted.

BKON is 5.3v when 24v is on AND off, pointing to a good mainboard, correct? BKADJ is also on 4.2v during both conditions.


I replaced the one cap under the heat sink where I thought the excess heat was coming from and no change.

I targeted the PWM controller IC with the air and no change.

I went back to the thought that it was the MOSFET and mounted some additional heat sinks to it, no change. I then tried to target the air coming from the fan as precisely as I could directly on the MOSFET. Doing this the TV ran for over 15 minutes.

Am I mistaken to think that the when the MOSFET heats up it is failing and cutting the 24v or is a bad cap or multiple bad caps a more likely cause?

Would and ESR meter help in determining which cap is the bad one?


Any thoughts on a tester like the one here:
http://www.ebay.com/itm/Multi-Use-Tr...item4abf8457a8

Am I wrong thinking heat build up some place or in some component and then cooling that area/component would point to the offending part? Or is that being to simplistic?

[martyparish]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

I suggest taking retiredcaps advice and replace all the junk caps. At around $1 apiece that's not a big gamble.

[budm]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

BKON = BACKLIGHTS ON
BKADJ = Backlights dimming.
So does the PS_ON disappear?, no PS_ON = No 24V.
And when PS_ON disappear, the PFC Voltage booster will shutdown, so check the DC voltage on the two legs of that large filter cap, at stand by will be about 170VDC, when TV is running, it will be about 380~400vdc.

[Mad Capper]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

The outputs do not have PS_ON designation, only -5,5,12,24,BKON,BKADJ,STB,GND.

Would PS_ON have another designation or is this located on the mainboard and not the power supply?

Of these the only thing that changes on the outputs when the video shuts off is all the 24v. I always get 0 on the -5v.

Main cap is 165v when tv is off/standby, 390v when on and when video shuts off.

[tom66]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

STB is PSON on this model.

[Mad Capper]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

STB is 0.1v when tv off and 3.4 when tv is on and when video shuts off.

[tom66]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

In which case the issue is somewhere on the PSU. Try resoldering all major solder joints.

[budm]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

Also check the VCC pin of IC3 to see if the voltage is still there when 24v goes away, this VCC is generated by the standby power suppy and fed through a switched transistor.

[Mad Capper]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

Again, thanks for all the help I appreciate it.

The reading for IC3 are:

When on
Pin1: 15.6
Pin2: 1.5
Pin3: 0
Pin4: 0
Pin5: 2.6
Pin6: 15.6
Pin7: 0
Pin8: 0


When video shuts off
Pin1: 0
Pin2: 4.1
Pin3: 0
Pin4: 0
Pin5: 0
Pin6: 15.5
Pin7: 0
Pin8: 0

Would this therefore indicate that one of the switched transistors is not functioning? Any ideas as to what the most likely one would be?

Or according to (http://www.scribd.com/doc/75492186/2...PWM-Controller) : Pin 1 connects to the VCC pin 6 and provides bias to the PFC controller. It goes down in standby and fault conditions.

Would this indicate that this component is faulty or the fault is coming from another source, e.g. the a switched transistor as mentioned?

Going to resolder next and see if that changes anything.

[budm]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

Pin 6 is the VCC to run the IC, it is OK on that pin but if pin 1 is 0, then the PFC should not be working, but since it is still working, it means that this pin 1 may not be hooked up to the PFC ic.

[Mad Capper]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

I resoldered all the through hole items and the 4 main ICs on the bottom of the board and still no change.

Which one is the PFC ic?


In the same area as the MOSFET near the bottom of the right hand heat sink is a ceramic capacitor. This is where I had been targeting the cooling. Upon further inspection it seems to be bad, see attached. There is a light brown discoloration as well that is hard to see in the scan.

Does this have the appearance of a bad disc capacitor? In its condition would this explain it working for a set time then shutting off and also continuing to work when cooling is applied?

It is a 101 1KV, so far I have only been able to find a 151 1KV capacitor in my parts inventory. Would this be acceptable to substitute or is it to far of a jump in capacitance?

Also just found from a CRT monitor board a 101 2KV and a LB 101K 1KV. Not sure what the LB signifies but seeing as the original does not have a tolerance value and this one is 10% would it be ok to use or would going with the higher voltage, 101 2KV be better?

Thanks

[budm]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

100pf 1kv. You can use higher voltage which will be better if it fits the board.
http://www.mouser.com/ProductDetail/...IG00s5spZjc%3d

[Mad Capper]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

I replaced the capacitor with the 101K 1KV that I had and after a series of 30 minute tests everything seems to be working. Hopefully everything stays that way.

I guess that means I should look a little harder at each component next time.

I think I am going to try to put a small fan in anyway to help dissipate some of the heat.

Again, thank you all for your assistance. It is greatly appreciated.

Now I just have to figure out how to fix the DVD player, never had much luck with those or CDROM drives.

[retiredcaps]

Re: Insignia NS-LTDVD26 Video shuts off after 10 minutes

I guess that means I should look a little harder at each component next time.

Good job on finding the bad component.

Many people don't realize how difficult remote troubleshooting is when we don't have the board in front of us. Even with excellent clear focused pictures (hence the ability to see some solder ring cracks), we only get one perspective and unless the component is obviously damaged, it is very difficult to spot.