Hi everyone, I am new to this forum. I would like to seek help on identifying a tiny diode in a switch mode power supply board in a Panasonic LED TV. The diode (D407 on the circuit board) has been circled in yellow in the attached photo. I have also attached the portion of the schematic with D407 diode highlighted in green. Unfortunately, this schematic diagram which I have found on the web does not provide any details on the components. The diagram only shows the circuits with no values stated for the components.

I have desoldered the diode out of the circuit and measured it with DMM using diode mode and the voltage value is around 0.173 which I think it unusually low and may be defective. The reverse reads OL. The markings on the diode is IK4 6A. Many thanks for your help!

 

Hi everyone, I am new to this forum. I would like to seek help on identifying a tiny diode in a switch mode power supply board in a Panasonic LED TV. The diode (D407 on the circuit board) has been circled in yellow in the attached photo. I have also attached the portion of the schematic with D407 diode highlighted in green. Unfortunately, this schematic diagram which I have found on the web does not provide any details on the components. The diagram only shows the circuits with no values stated for the components.

I have desoldered the diode out of the circuit and measured it with DMM using diode mode and the voltage value is around 0.173 which I think it unusually low and may be defective. The reverse reads OL. The markings on the diode is IK4 6A. Many thanks for your help!

Hi E,
It could be this?
https://www.alibaba.com/product-detail/6A10-Rectifier-diode-6A-1000V-electronic_60743498896.html
C.

 

Hi E,
It could be this?
https://www.alibaba.com/product-detail/6A10-Rectifier-diode-6A-1000V-electronic_60743498896.html
C.

Thanks! Do you think the IK4 in the markings is referring to 1K volts ie. 1000 volts? What do you think the 4 means? Thanks again!

 

Thanks! Do you think the IK4 in the markings is referring to 1K volts ie. 1000 volts? What do you think the 4 means? Thanks again!

Hi E,
I'm no expert, but perhaps 400V surge current?
Good luck
C

 

It would appear that the control IC is a Sanken STR-A6051M, 22W switched mode IC. The diode in question is across the current sense resistor (R405). It doesn't appear in any of the application circuits, which implies that it would be perfectly OK without it.
22W output would suggest an average current of 67mA through R405 for a 230V supply, so a peak current of about 0.4A.
The voltage across the current sense resistor should not exceed 1V. It's probably there as a protection diode as the current sense input might not like a reverse bias, and there may be some oscillation due to the snubber cap (C405) and inductor (L402)
I think therefore it is probably a 30V 1A schottky, which would have a forward volt drop of about 0.15V, exactly as you measured.

 

Hi,
Lesson: always get a second opinion
C

 

It would appear that the control IC is a Sanken STR-A6051M, 22W switched mode IC. The diode in question is across the current sense resistor (R405). It doesn't appear in any of the application circuits, which implies that it would be perfectly OK without it.
22W output would suggest an average current of 67mA through R405 for a 230V supply, so a peak current of about 0.4A.
The voltage across the current sense resistor should not exceed 1V. It's probably there as a protection diode as the current sense input might not like a reverse bias, and there may be some oscillation due to the snubber cap (C405) and inductor (L402)
I think therefore it is probably a 30V 1A schottky, which would have a forward volt drop of about 0.15V, exactly as you measured.

Thanks for the detailed analysis! I got a reply from another forum who also concluded that the diode is a schottky. But my only reservation is that the schematic diagram symbol for the diode (R405) is only showing the normal diode symbol and not the schottky diode symbol. I am a beginner at electronics and just starting to learn the basics as I am trying to repair the LED TV power supply board. I have checked most of the diodes and capacitors on the board and cannot find any faults. I am now kind of stuck not knowing what else to check. Do you have any suggestions as to any books or guides which may be useful for LED TV power supply board repairs? Many thanks!

 

Hi E,
I'm no expert, but perhaps 400V surge current?
Good luck
C

Thanks! I need all the luck I can get.

 

The two design topologies used in TVs are either flyback (lower power) or LLC resonant (higher power). Flyback has one power transistor on the primary side, LLC has two.
There's loads of literature on how a flyback power supply works, because they are so common.
LLC is either Fairchild
https://www.onsemi.com/pub/collateral/an-4151.pdf
or Power Integrations
https://www.power.com/design-support/design-examples/der-270-125-w-llc-dc-dc-resonant-converter

 

The two design topologies used in TVs are either flyback (lower power) or LLC resonant (higher power). Flyback has one power transistor on the primary side, LLC has two.
There's loads of literature on how a flyback power supply works, because they are so common.
LLC is either Fairchild
https://www.onsemi.com/pub/collateral/an-4151.pdf
or Power Integrations
https://www.power.com/design-support/design-examples/der-270-125-w-llc-dc-dc-resonant-converter

Thanks!