Sony TV green LED present, red LED missing

[DjKrish]

Suddenly this sony led tv red light gone missing When put on standby the red should come ON. When turn on the tv, the green is working fine. Otherwise the tv has no problem. Is the LED damaged or i need to change the entire IR board?

Model klv-40s550a

[budm]

Re: Sony TV green LED present, red LED missing

Just check the DC Voltage between Anode leg and Cathode leg of that RED LED to see what you get.

[DjKrish]

Re: Sony TV green LED present, red LED missing

Tested those led with MM. Both led working fine. While on standby, no voltages going to red led. Zero

[budm]

Re: Sony TV green LED present, red LED missing

That means you have to look at the LED driver circuit next.
May be it has open circuit some where.
What Voltage do you get at each leg if measured against circuit GND (the LED may be driven by high side switching (source) or low side switching (sink)).

[DjKrish]

Re: Sony TV green LED present, red LED missing

On the green, i get about 2.20v while the tv is on. LED driver circuit as in on the main board, right?

[budm]

Re: Sony TV green LED present, red LED missing

The driver circuit should be on the main board but that depends on the design, may be you should provide the pictures of the boards.
So how about the Voltage reading with reference to GND against the Anode and the Cathode of the RED LED? That will give us more clue as how the LED is driven.

[DjKrish]

Re: Sony TV green LED present, red LED missing

Here are the readings :

Green LED on tv ON mode : 0.02v + / 1.93v -
Green LED on tv standby mode : 3.37v + / 1.79v -

Red ON and standby : Zero voltages going to + and - from ground point

[budm]

Re: Sony TV green LED present, red LED missing

The LED/IR board looks like it has 4 SMD Transistors on it, so some of them may be for driving the LEDs; I cannot really tell for sure.