Insignia 32" LCD TV Model# NS-32LCD

[Paul678]

Re: Insignia 32" LCD TV Model# NS-32LCD

That kind of makes sense, I don't suppose you saw a picture during the flickering? The lack of PWM control probably confuses the inverter, but it's at least attempting to light the tubes. Looks like main board at fault then.

No picture. I was looking for a "no signal", or menu, as
I was pressing the menu button, but nothing. Just a dim
flashing.

Are you certain the faint ticking from the power supply is
normal? It's faint, but audible, and I've never heard a
SMPS make this kind of noise. It's the first thing I noticed
when I turned it on. I checked the back of the ps, and
it looks normal. No bulging caps or nothing.

If it's the main, they are going for about $50 on Ebay.....I'll
have to think about this one, because I sold the last
NS-32LCD I fixed for only $180.

[tom66]

Re: Insignia 32" LCD TV Model# NS-32LCD

I'm sure you can fix it, rather than just doing a board swap. The ticking is probably because the inverter draws a lot of power to get the tubes to light, but then the power consumption drops. When it doesn't seem PWM from the main board, it probably shuts down. Not certain though.

Post a pic of the main board - you can check the voltage regulators, fuses, switchers etc.

[budm]

Re: Insignia 32" LCD TV Model# NS-32LCD

If the 24vdc power supply is good, then it should be able to make inverter run without fluctuation, I would monitor the 24vdc to see if it is going up and down since the 24v power supply is rated to run the inverter board. The 24v power suppply is more likely to be rated at 4~5A.

[tom66]

Re: Insignia 32" LCD TV Model# NS-32LCD

You could always try some car headlamp bulbs, as budm has suggested before.

[Paul678]

Re: Insignia 32" LCD TV Model# NS-32LCD

If the 24vdc power supply is good, then it should be able to make inverter run without fluctuation, I would monitor the 24vdc to see if it is going up and down since the 24v power supply is rated to run the inverter board. The 24v power suppply is more likely to be rated at 4~5A.

Regarding your suggestion of car lamps: just put them on the +24V
line, and see if the brightness is steady?

[budm]

Re: Insignia 32" LCD TV Model# NS-32LCD

You put the two 12v car lamps in series so they will handle 24vdc voltage.

[Paul678]

Re: Insignia 32" LCD TV Model# NS-32LCD

You put the two 12v car lamps in series so they will handle 24vdc voltage.

Ok, I've got a bad power supply, as I suspected. It's
just not normal to hear that kind of "ticking" sound, even
if it's rather faint.

I hooked my ancient Tektronix 564 to the 24V line, and
with OR WITHOUT the 24V connectors hooked up, there is
an awful 4-5 volt spike in the voltage, which is in synch
with the ticking sound:



Just a reminder of the limitations
of a DMM, as it showed a steady 24V when measured on
that.

Even the 5V standby line gets screwed up as soon as the
power supply is enabled. 5V standby by itself is nice and
steady.

Ok, here is the supply (sorry it's not lit very well):



And the cheapest I found it ($35 free shipping) was here:

http://www.rivervalleyelectronics.ne...-32fb26-20.htm

I wouldn't mind spending some time trying to
troubleshoot at component level, but as usual,
I couldn't find a schematic.

The board reads 782.32FB26-2000

[budm]

Re: Insignia 32" LCD TV Model# NS-32LCD

That is one reason I use lamps for testing the power supply output since your eyes can easily see the lights fluctuation, but my Fluke 87 also has the bar graph display that response pretty fast to the voltage changes.

[tom66]

Re: Insignia 32" LCD TV Model# NS-32LCD

There are two small caps on the primary side of the power supply. These tiny caps almost always fail without bulging, and they're dirt cheap. They are a common cause of this problem with pulses on the output. You can use a generic (e.g. RadioShack ) capacitor to replace them in most cases, but it would be advisable to later replace them with high reliability general purpose capacitors.

[budm]

Re: Insignia 32" LCD TV Model# NS-32LCD

Yes Tom, I suspect that small elctrolyics cap on the left of that large cap toward the bottom of the picture.

[Paul678]

Re: Insignia 32" LCD TV Model# NS-32LCD

Yes Tom, I suspect that small elctrolyics cap on the left of that large cap toward the bottom of the picture.

Are you guys talking about the 2 small electrolytics, within the
dotted lines, in the picture I posted? One of which is to the left
of the huge electrolytic near the center?

In what way do they fail? I took them both out, and the
appear to test ok, about 8uF each, and no shorts. But
I don't have an ESR meter.....

[budm]

Re: Insignia 32" LCD TV Model# NS-32LCD

Please see the PDF.
This power supply has PFC Voltage booster circuits, the voltage on that big cap should be about as shown when the TV is on, and lower when TV is OFF, see if the DC voltage is fluctuating, becareful if you are going to use the scope on the hot side, the TV must be plugged into isolation transformer otherwise you will damage the TV power supply. 8uF that is odd value.

[Paul678]

Re: Insignia 32" LCD TV Model# NS-32LCD

Please see the PDF.
This power supply has PFC Voltage booster circuits, the voltage on that big cap should be about as shown when the TV is on, and lower when TV is OFF, see if the DC voltage is fluctuating, becareful if you are going to use the scope on the hot side, the TV must be plugged into isolation transformer otherwise you will damage the TV power supply. 8uF that is odd value.

344V on the big cap when TV is on.

When turned off, the big cap appears to discharge.

I replaced the small cap you suspected (10uF, 25V),
with a 10uF, 50V i stole from another board. Same problem.

[budm]

Re: Insignia 32" LCD TV Model# NS-32LCD

the 344vdc is steady, not going up and down in sync with the symptom?

[Paul678]

Re: Insignia 32" LCD TV Model# NS-32LCD

the 344vdc is steady, not going up and down in sync with the symptom?

It appears to have the symptom on it.

[budm]

Re: Insignia 32" LCD TV Model# NS-32LCD

So it can be that the PFC is having the problem (not able to supply enough power for the 24vdc power supply) or the 24vdc power supply is having the problem (drawing too much power). I have to think about it to see how to isolate the cause of the problem.
It can be that large DC filter cap is bad.

[tom66]

Re: Insignia 32" LCD TV Model# NS-32LCD

So it can be that the PFC is having the problem (not able to supply enough power for the 24vdc power supply) or the 24vdc power supply is having the problem (drawing too much power). I have to think about it to see how to isolate the cause of the problem.
It can be that large DC filter cap is bad.

Usually when the primary cap fails, it takes out the PFC. Because the boost voltage has no where to go it shorts the diode. Sometimes the PFC FET survives, sometimes it doesn't.

[Paul678]

Re: Insignia 32" LCD TV Model# NS-32LCD

So it can be that the PFC is having the problem (not able to supply enough power for the 24vdc power supply) or the 24vdc power supply is having the problem (drawing too much power). I have to think about it to see how to isolate the cause of the problem.
It can be that large DC filter cap is bad.

I replaced the large filter cap with an approximate
equivalent, and still the same problem.

Without a proper schematic, debugging this thing won't
be easy, if the problem is not something obvious.

Even WITH the schematic, debugging can be tough,
but without it, it's like walking through a pitch black
forest.

Too bad all this stuff is proprietary......

[budm]

Re: Insignia 32" LCD TV Model# NS-32LCD

Agree!

[tom66]

Re: Insignia 32" LCD TV Model# NS-32LCD

344V on the big cap when TV is on.

When turned off, the big cap appears to discharge.

I replaced the small cap you suspected (10uF, 25V),
with a 10uF, 50V i stole from another board. Same problem.

Did you replace the other small cap?