NAD Tuner 412 display problem

[fishing518]

The back-light bulbs behind the LCD of my NAD 412 tuner went out. I checked out online. Someone said the voltage is about 12v. But there is no information of current running through. I am planning to use some LED instead. Would anyone kindly let me know what the current is such that I can choose the right resistor for LEDs.

Thanks as always.

 

[JBL GUY]

The current that was drawn by the original lamps is not an issue.

The purpose of the series resistor that is used with the LED is to limit the current through the LED. The current will likely not be the same with the LEDs and that will be fine.

You need to determine the actual voltage present and determine if it is an AC voltage or a DC voltage.

Here is a link to one of many LED resistor calculators.

LED RESISTOR CALCULATOR

If it is an AC voltage and you only use 1 LED, you will need a separate protection diode to protect the LED from excessive reverse voltage.


If you are going to use 2 diodes you can connect the diodes in parallel, but opposite polarity. If you decide to do this, use the top calculator to determine the value of the resistor, but connect them like the bottom diagram, but reverse the polarity of one of the diodes. You will not need a separate reverse voltage protection diode in this application.

If you need more than 2 LEDs, you may use the middle circuit with a separate diode to protect the LEDs from excessive reverse voltage.

The separate diode would be connected in series with the LEDs.

A 1N4001 diode would work fine if your supply voltage is 12 VAC.

If the voltage present is a DC voltage, you will need to pay attention to the polarity, but you will not need the separate protection diode.

I just read my post and it is not as clear as I would like it, but it is my medications.

Anyone may feel free to add to or correct my post.

 

[fishing518]

The current that was drawn by the original lamps is not an issue.

The purpose of the series resistor that is used with the LED is to limit the current through the LED. The current will likely not be the same with the LEDs and that will be fine.

You need to determine the actual voltage present and determine if it is an AC voltage or a DC voltage.

Here is a link to one of many LED resistor calculators.

LED RESISTOR CALCULATOR

If it is an AC voltage and you only use 1 LED, you will need a separate protection diode to protect the LED from excessive reverse voltage.

By the way, according to what I found, it is DC 12v for the NAD back-light bulb.


If you are going to use 2 diodes you can connect the diodes in parallel, but opposite polarity. If you decide to do this, use the top calculator to determine the value of the resistor, but connect them like the bottom diagram, but reverse the polarity of one of the diodes. You will not need a separate reverse voltage protection diode in this application.

If you need more than 2 LEDs, you may use the middle circuit with a separate diode to protect the LEDs from excessive reverse voltage.

The separate diode would be connected in series with the LEDs.

A 1N4001 diode would work fine if your supply voltage is 12 VAC.

If the voltage present is a DC voltage, you will need to pay attention to the polarity, but you will not need the separate protection diode.

I just read my post and it is not as clear as I would like it, but it is my medications.

Anyone may feel free to add to or correct my post.

Thanks JBL for clearing the cloud.

So, about "the current is not an issue", does this mean it is not an issue for the LED. Will it affect the tuner as a whole, for example, will it blow the fuse?

I am sorry for the dummy question. I just started to do some LED conversion for this NAD and another Yamaha.

 

[JBL GUY]

I meant that you do not have to worry about the original current draw with the original lamps.

The current that your LEDs will draw will probability be less than the current draw of the original lamps, so the final current draw of your conversion should not be an issue. Although I do not have a service manual for this unit, so I do not know the rating of the original lamps.

I took a quick look on line and did not see a service manual, maybe someone here can supply you with the specifications for the original lamps.

What is the current rating on the LEDs that you plan to use? Most LEDs will operate at a lower current draw without a large reduction in the light output.

You may want to experiment with the current to obtain the needed brightness for the display.

You may also need to soften the output of the LEDs so that the output is more even, in the manner of the original lamps. What you do to obtain even illumination will depend on your display.

 

[fishing518]

I meant that you do not have to worry about the original current draw with the original lamps.

The current that your LEDs will draw will probability be less than the current draw of the original lamps, so the final current draw of your conversion should not be an issue. Although I do not have a service manual for this unit, so I do not know the rating of the original lamps.

I took a quick look on line and did not see a service manual, maybe someone here can supply you with the specifications for the original lamps.

What is the current rating on the LEDs that you plan to use? Most LEDs will operate at a lower current draw without a large reduction in the light output.

You may want to experiment with the current to obtain the needed brightness for the display.

You may also need to soften the output of the LEDs so that the output is more even, in the manner of the original lamps. What you do to obtain even illumination will depend on your display.

Thanks JBL,

I am looking at some LEDs with current of 20ma.

As to the brightness, I did find it is exactly like what you said. I use some LEDs from some junk equipment and use a resistor to do some experiment. The brightness is almost like nothing. It did light up but barely make the LCD readable.

I checked some LEDs online, they all say "high intensity light" but I have no clue about how bright it will be and how much it will shine up the LCD. Also some said diffused LED, honestly, I don't have any first-hand experience about the brightness.