Replace display bulb with LED on NAD cd players

[Mikelo]

I have been replacing the bulbs on a NAD 502
and a 512 display, but they burn out every couple of
years and would like to replace the incandescent
bulbs with LEDs. I tried an intuitive approach
and used a LED with the appropriate resistor
between anode and the 15 volts, but that did
not work. Somewhere online I saw that to do
this you also need a capacitor and a diode.

Any hints, advice, links, diagrams, etc. would
be very much appreciated.

[amc184]

I've replaced the bulbs on a NAD 705 with LEDs successfully. That was as simple as a LED and a dropper resistor to replace each bulb.

However, the bulb supply on a NAD 705 is DC, and if people were talking about putting a capacitor in the mix, the 502 and 512 may use an AC bulb supply.

Check whether the bulb supply is AC or DC, and we'll be able to help you further.

[Praudio]

If your 15v is DC(and presume your bulbs is 12V) just use diodes string each one drop about .6v , if AC go with .25/.50 ohm 10w to drop around 12V.

[Mikelo]

Is it possible that the resistor was too high? I was using a 560
ohm resistor. But it turns out it was a 30mA, 5V led, which means
given that the supply is 15vdc I need a 336 ohm resistor.

[Bill_P]

Originally Posted by Mikelo

Is it possible that the resistor was too high? I was using a 560
ohm resistor. But it turns out it was a 30mA, 5V led, which means
given that the supply is 15vdc I need a 336 ohm resistor.

I found the service manuals for the 502 and 512 on the web. Both schematics show two 16V incandescent bulbs connected in parallel and fed from -15VDC, not +15VDC. You probably have the LED(s) connected backwards if you were expecting a +15VDC source.

Regarding the LED, 30mA seems high - what LED are you planning to use? It should still light up with 560 Ohms in any case. I would wire the LED's in series with an appropriate resistor to set the current to the recommended value from the datasheet.