Insignia NS-L46Q120 - TV Shuts Down - Apparently Bad T-Con Board

[bobbyskillz]

Hello! I have a fun one (I think). It's an Insignia NS-L46Q120 that shuts down after several minutes of being powered on. It can be powered right back on, but the run time shortens with each consecutive power cycle. All voltage readings at the connector are consistent with specifications - both standby and running.

When the T-Con board is disconnected, the TV stays on indefinitely. Is this an unusual failure mode for a T-Con board? I couldn't see anything obvious at first glance and found no hot spots after failure. I would really love to do a component level repair on this - something I can learn from. Has anyone ever seen this symptom before? Am I right that the T-Con board is the culprit? What the most obvious approach to narrowing down the failure on this board?

Thanks for any input you might give.

[budm]

Re: Insignia NS-L46Q120 - TV Shuts Down - Apparently Bad T-Con Board

1) So you do have all the control signals?
2) "When the T-Con board is disconnected, the TV stays on indefinitely." So the backlights do come on and stay on?
3) So do you have 12VDC at both ends of the SMD fuses on the T-CON board?
4) Will the TV stay on if the ribbon cable between the T-CON and the LCD panel are disconnected?
5) There are many Voltage test points on the T-CON board, did you test them?

[bobbyskillz]

Re: Insignia NS-L46Q120 - TV Shuts Down - Apparently Bad T-Con Board

Thanks for the reply, budm.

1) So you do have all the control signals?

Yes. It appears so.

2) "When the T-Con board is disconnected, the TV stays on indefinitely." So the backlights do come on and stay on?

The backlights come on and stay on indefinitely with the T-Con disconnected and power toggled on.

3) So do you have 12VDC at both ends of the SMD fuses on the T-CON board?

Yes. 12VDC is testing at both ends of the fuse.

4) Will the TV stay on if the ribbon cable between the T-CON and the LCD panel are disconnected?

No. With the two ribbon cables to the panel disconnected, the symptoms remain the same. The only way to keep power on is to disconnect the T-Con board.

5) There are many Voltage test points on the T-CON board, did you test them?

I'm going to do this tonight and see what I can find.

Is this a fairly unusual failure mode for a T-Con board?

[budm]

Re: Insignia NS-L46Q120 - TV Shuts Down - Apparently Bad T-Con Board

Can you get the LCD panel model number? There should be a sticker on the LCD panel some where then we can look up the spec sheet of the LCD panel and see if the T-CON has any error signal output the goes back to the main board or not.
The Voltage tests points may give you some clues if all the switching power supplies and Voltage regulator IC's are OK or not, or it can be as simple as shorted MLCC (Mutlti Layer Ceramic Cap) on the T-CON.

[bobbyskillz]

Re: Insignia NS-L46Q120 - TV Shuts Down - Apparently Bad T-Con Board

The panel is a T460HW03.

I probed around some more and discovered the 12v gradually diminishes to 11.5v - at which point the set shuts off

I removed the small thermal pad and discovered a RT8269 buck converter underneath. I haven't finished thumbing through the datasheet on this yet, but I wonder if this could be a suspect?

[budm]

Re: Insignia NS-L46Q120 - TV Shuts Down - Apparently Bad T-Con Board

"T460HW03" there should be V? after the model number to tell which version the LCD panel is.
Is it VF, V1, etc.?

VF:

[bobbyskillz]

Re: Insignia NS-L46Q120 - TV Shuts Down - Apparently Bad T-Con Board

It's a T460HW03 V5.

I looked at the buck converter output; it looks steady and normal. It's the 12v input on the board that drops gradually within a period of about fifteen seconds. I haven't found any shorted caps yet.

[budm]

Re: Insignia NS-L46Q120 - TV Shuts Down - Apparently Bad T-Con Board

There are many Voltage buck, boost converters to generate VGH (+15 ~20V), VGL (-6 ~ 10v), VDD, etc. + LDO regulators.
You need to list the Voltage readings of the test points.

[bobbyskillz]

Re: Insignia NS-L46Q120 - TV Shuts Down - Apparently Bad T-Con Board

Thanks, budm. I'm going to go through and try to read those values. When I was probing around, I found a diode that is short to ground at both the anode and cathode only when the main board is connected. If I disconnect the LVDS cable from the main board, the diode appears to function normally. Could this be a clue to the problem, or is it useless without a clear schematic?

[budm]

Re: Insignia NS-L46Q120 - TV Shuts Down - Apparently Bad T-Con Board

So the resistance between Anode and circuit GND is 0 Ohm, same for Cathode and circuit GND when connected to the main board?
What connector pin is that DIODE D0002 connected to?