Insignia LCD TV NS-L32Q-10A screen blinking...

[Howard_Woodard]

After being turned on for about 5 minutes the screen will start to blink black -- as quick as an eye blink. The longer it stays on the more often it blinks until it is blinking fast enough to run a rock concert light show or cause siezures. It happens no matter what input or picture mode is selected and, other than the blink, everything else, picture, sound, etc. works perfectly.

It's a pretty simple TV with a small button board, a main board, a power board and an inverter board. There are a lot of things that could effect all modes and inputs but I figured the most likely one would be something to do with the power board or the HV inverter board.

All caps on all of the boards look good -- no swelling, no discoloration of the cap or surrounding areas.

I measured the output voltages from the power board and all are exactly where they should be. I noticed that the +24vdc going to the inverter would "tick down" when the screen would blink but I'm guessing that was just in reaction to the quick load change coming from the inverter. With the inverter disconnected all voltages were correct and stable.

I measured the primary and secondary windings of all of the inverter HV transformers with an ohm meter and they all appeared correct -- low imp primary, high imp secondary and all approx. the same.

So, while I don't have anything definitive, other than observation, my gut tells me this is an inverter problem. I'm not an electronics tech [though I worked as a radar repairman in the USAF and know a little bit] and the only instrument I have is a multimeter.

Anyone familiar with the Insignia line? Do these symptoms ring a bell? If so, what is the most likely defect that will cause the LCD backlight to blink like this?

Thanks in advance.

Howard -- Blinking in Seattle

[budm]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

The bl_on (on/off) signal to the inverter board is steady, same for the Dim signal?

[tom66]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

Blinking backlight can be indicative of a problem with the 450V capacitor.

[Howard_Woodard]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

It's the back light that is winking out. The 24 vdc output from the power board "ticks" slightly when the light blinks but I suspect that is just because the load changes. With the inverter unplugged all voltages are correct and stable. In fact, everything works perfect with no interruptions even when the backlight is blinking.

I measured the primary and secondary windings of all of the HV transformers. They all seemed ok and were almost identical in their resistance readings. All of the capacitors look ok - no deformations or discolorations.

It seems to me that the backlight would be something that should stay on all the time so not too likely to have much in the way of controla coming from the other boards. That's the basis for my suspicion that the problem is in the inverter board itself.

What do you think?

[budm]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

If the BL_ON signal comes on goes, it will turn the inverter on and off, so the 24v power supply will be seeing the inrush current every time the inverter turns on, that is why I ask to check the BL_ON pin.

[truep]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

Does this set have a cable between the inverter and the TCON? If so, try disconecting the cable and see if it changes.

[budm]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

Is this the inverter board you have?
http://assets.shopjimmy.com/media/ca...03.013-top.jpg
If it is, it uses sockets for the board to lamp connections, you can try re-seating the board and also look real close at the sockets to see if it has any corrode, burn marks, etc.

[Howard_Woodard]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

Ok, sorry for taking so long to get back to you folks.

When the TV is on, warmed up, and the backlight is blinking, the DIM is a steady +3.239 vdc and the on/off is a steady 3.23 vdc. No change when the backlight winks off and on.

Yes, the picture shown is my inverter board and all of the sockets look shiny with just the slight depression where the contact is made. It does not have a cable to the T-CON board.

The big 450 Volt capacitor looks pristine as do all of the connectors and pins.

I don't have more detailed circuit diagrams. I can measure a few things for stability or consistency but don't know what the readings should actually be.

As I said earlier, I have measured primary and secondary windings on all of the HV transformers while powered down and cold and they read ok. But since it only blinks after a few minutes of power on and I haven't attempted any inverter readings [beyond the 24 vdc, DIM and on/off from the power control board] after it is warmed up and blinking I can't say whether one of the inverter components is failing when warm or not but it really looks that way.

Used inverter boards aren't very expensive on eBay so unless I have an epiphany between now and next Monday morning I'll probably order one.

Still open to input...

[budm]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

That is good to know that the control signals are steady. You may try this to see if the lamp itself has stop working by using the video source to show white screen, if one of the lamp goes off, you may be able to see the dark section shown on the screen if you can catch it fast enough. Otherwise I do not have any other suggestion, sure would like to know the cause.

[Howard_Woodard]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

Thanks budm. I have confirmed that the backlights are all going out -- the entire screen.

[tom66]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

I have seen the 450V capacitor on the power supply (primary side) dry up cause this problem. Check the voltage across it while operating; can you post a picture of the power board? Note, I've had them look good and still be bad. They're quite bad for not obviously failing.

[Howard_Woodard]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

[Howard_Woodard]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

The voltage across the capacitor with the inverter board disconnected is a steady 395.5.

With the inverter plugged in it is a steady 391.2 and doesn't even tick when the backlights wink off and back on.

When the TV is turned off the capacitor discharges fairly quickly to about 155-160 volts and then very slowly from there on down.

Looks to me like the capacitor is fine. Not sure if I should really be expecting 400 volts or if the 390 is good enough. I suspect the latter.

[Howard_Woodard]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

Well, maybe I mislead myself...

The 24 VDC lines to the inverter board are dipping to about 16 VDC each time the backlights go out -- maybe more but that's as quick as my little multimeter can react. When I measured these voltages before they looked like they were just "ticking" when the lights would blink -- more like a reaction to the load change than the cause of it.

Think I'll spend a little time troubleshooting the power board -- particularly the 24 VDC supply.

[budm]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

Then we need to verify again that the BL_0N also did not dip down.

[Howard_Woodard]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

Thanks for your quick response. I have verified that the pins marked on/off for the connector going to the main board and the connector going to the inverter board appear as a very steady 3.28 VDC. In fact, all of the pins marked as DIM or On/Off read about 3.28 VDC and all of the pins marked 5 V read 4.95 and all are steady, showing no ticks on my meter.

Without an oscilloscope -- I don't have one or access to one -- I can't see really quick changes, much less measure them. The backlight wink/blink is about a quarter of a second and my digital multimeter shows about about a 30% drop on the 24 volt lines going to the inverter and the 12 volt lines going to the mainboard.

I do not have a pin marked BL-ON on either of these connectors.

[budm]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

That is good to know for sure, since the 24v cannot maintain its output at 24V, so we need to look at the 12v/24v circuit next.
The hard part will be tracing out the board to see how they are connected and what kind of SMPS IC is use for this section.

[Howard_Woodard]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

Well, I don't have the test equipment to test the components on the board. Might be able to if it had been a hard failure but one that only happens after it has warmed up and the only cyclically is pretty tough. At any rate, a new power board delivered to my door was only $25 and that fixed the problem. Of course I would have loved to have fixed it for $2-$3 for a capacitor or MOSFET but $25 isn't too bad.

Thanks to all for your help with this.

BTW, the reason there are lots of boards available for this TV is that so many of them end up with broken screens and people just salvage the parts rather than replacing the screen.

Thanks again all.

[budm]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

Thanks for the repair feedback, $25 for power supply board is very reasonable price.

[thro]

Re: Insignia LCD TV NS-L32Q-10A screen blinking...

Hello,
I have used this site before for a tv that had bad caps on the power board and was happy to fix it for less than $2. The info here is excellent. Anyway a friend asked me to check out his tv. The problem is there is a red light in standby and then turns blue when you turn it on, a quick screen pops up saying "Please wait..." and screen goes dark and stays that way, no picture or sound.

I looked at the caps on the power board and all seem good, I also have these readings on the board:

standby (red) - On (blue)
on/off - 0v - 3.33v
PDIM - 0v - 2.99v
+12 - 0v - 12.35v
+12 - 0v - 12.35v
GND
GND
+24v - 0v - 25.21v
+24v - 0v - 25.21v
PS_ON - 0.11v - 4.73v
+5v - 5.21v - 5.21v
+5v - 5.21v - 5.21v

Large Black cap 155v - 397v

I am not an electronic tech, I do electrical work and tinker with this stuff.

Any help would be appreciated

Thanks