Insignia NS-29LD120A13 Keeps restarting

[Ceredox]

Hey guys and gals. I have an Insignia NS-29LD120A13 that i got from a friend and it keeps restarting about every 6 and a half seconds or so. Heat doesnt seem to be a facor - i tried the localized blow dryer method and it didn't make any difference. Its always at 6.5 seconds every time. I'm certain that it is a power supply problem because the whole TV powers off completely and restarts but i'm seeing no physical signs. The supply seems hard to find so id prefer to fix it. When its running, the big capacitor on the power side has 325.8 VDC and when the tv restarts, it retains that voltage. Same goes for the audio amplifier and the transisters. Keep in mind that mi'm not sure what these components should actually be running at. It's just acting as if someone unplugged the TV and plugged it back in. Anyone have any thoughts as to what this could be?

Thanks,
Josh

[budm]

Re: Insignia NS-29LD120A13 Keeps restarting

Is this the power supply?
Megmeet MIP293 Power Supply / Backlight Inverter
http://www.shopjimmy.com/megmeet-mip...t-inverter.htm

Do you still get 325VDC between the two legs of the main filter cap if the cable between the main board and the power supply board is disconnected?
Pictures of YOUR board?

[Ceredox]

Re: Insignia NS-29LD120A13 Keeps restarting

Is this the power supply?
Megmeet MIP293 Power Supply / Backlight Inverter
http://www.shopjimmy.com/megmeet-mip...t-inverter.htm

Do you still get 325VDC between the two legs of the main filter cap if the cable between the main board and the power supply board is disconnected?
Pictures of YOUR board?

Oh im sorry, i forgot to add the board model. Yes, that is the power supply.

So... since this post, i have a little backstory. While checking to see where power was lost when the TV restarts, I was checking voltage on the legs of one of the Mosfets. This one had about 70VAC and when i kept it on the legs, the TV actually stayed on. As soon as i took it off, the fuse blew and the mosfet started smoking. So i dont really trust it. I replaced it with one i had hanging around with very similar stats. (I am well aware that this isn't a great idea and don't make a habit of practicing it). I replaced the fuse and the TV turns on now and does the same thing. BUT the filer cap is running at 140Vdc now. I'm assuming that this is because of the component i substituted. I'm not going to leave it on for any extended period of time until i can get the correct one. But to answer your question, It reads 139v when the main board is plugged in and when i unplug it, it goes to about 165v. I don't know if this at least helps you a little. Although the values have been compromised. I'll remove the baord and get some pictures up as well.

[budm]

Re: Insignia NS-29LD120A13 Keeps restarting

If the Voltage reading between the two legs of the main filter cap was showing 325VDC, it means that the main board is getting the STBY Voltage to run and the main board is sending the PS-ON to turn on the PFC Voltage booster circuit to boost the DCV on the two legs of the filter cap to 325VDC which is by the way too low, it should be close to 400VDC.
BTW, are you using the chassis as the GND ref. for the meter when you are measuring the DCV in the primary (HOT) side of the circuit, if you did then your readings are invalid.

[Ceredox]

Re: Insignia NS-29LD120A13 Keeps restarting

Here are some pics of the board in question. Not sure exactly what you need some hopefully this helps somewhat. The second one from the left mounted on the heat sink is the one i replaced.

[budm]

Re: Insignia NS-29LD120A13 Keeps restarting

That is the Power MOSFET for the PFC Voltage booster circuit, so more likely the PFC Controller IC is also damaged, also check to see if RP2 is still showing <1 Ohm.

[Ceredox]

Re: Insignia NS-29LD120A13 Keeps restarting

If the Voltage reading between the two legs of the main filter cap was showing 325VDC, it means that the main board is getting the STBY Voltage to run and the main board is sending the PS-ON to turn on the PFC Voltage booster circuit to boost the DCV on the two legs of the filter cap to 325VDC which is by the way too low, it should be close to 400VDC.
BTW, are you using the chassis as the GND ref. for the meter when you are measuring the DCV in the primary (HOT) side of the circuit, if you did then your readings are invalid.

Ok, i did think that 325v was lower than what i usually hear people talk about but i wasn't sure if this TV was just different for whatever reason. I'm still pretty new at this. Do you know why that would be so low? No i didn't use the chassis. But it is very likely i didn't measure it right, I'm not fantastic with transistors yet. Usually, i'm looking for something very much out of the ordinary as opposed to what I've seen before.

Also, Do you have any recommendations on good articles to measure voltage across them? I do know how they work to some extent but in Tv's I shooting in the dark for the most part.

[Ceredox]

Re: Insignia NS-29LD120A13 Keeps restarting

That is the Power MOSFET for the PFC Voltage booster circuit, so more likely the PFC Controller IC is also damaged, also check to see if RP2 is still showing <1 Ohm.

RP2 is reading .5 Ohms.
I see 2 Ics on the hot side on the underneath of the board. Is one of those the one your referring to?

[budm]

Re: Insignia NS-29LD120A13 Keeps restarting

When PFC Voltage is too law, it usually due to faulty feedback circuit that is used to maintain the output Voltage, the resistors network in the feedback circuit were probably drifted in values.
I do not know how much you want to spend on 29" TV.

[Ceredox]

Re: Insignia NS-29LD120A13 Keeps restarting

I got it for free and i can buy a board for it but to be honest i'm mostly just interested in learning and trying to repair it This isn't really an investment for me. Money isn't much of an object as long as i get better at something.

[budm]

Re: Insignia NS-29LD120A13 Keeps restarting

At this point I would get the new Power MOSFET, the PFC Controller IC, and check that resistor I told you to check.