NAD 510 LED Backlight Modification

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The fuse had burt out on the PS of my NAD 510 CD Player that I had closeted some time ago. I got around to running down to the electronics store and picked up some 630mA 250V fuses so I could get 'er going again. Popped a new one it totally expecting it to blow again because knowing my luck, some transistor was stuck somewhere but YAY! Plugged it in and it fired up without a problem... Except one thing.... The backlights on the display had burnt out. So I pull the display apart to check out what I need to trot down to the electronics store to buy and low and behold. Incandecent lamps... I hate these bastards... Always burning out at the most retarted times and a bastard to replace too.

So I meter the line and it's 24v... Screw these damn bulbs. I'm going to convert to LED.

The backlight board has locations for three lamps, but the 510 only has two. The third in the middle is soldered over. I guess the original design in London way back in December of 1995 called for three but they figured it was too bright... Bright is good!!!

I was going to splice in a resistor in the V line from the mainboard to the front panel and heat shrink it to further drop the voltage to the 3.3V that I need for by blue LED's (Blue is so much cooler than white lamps) but that would have looked like ***. Even thought no one will ever see it... I'll know it's there...

So I traced back to the mainboard and a big *** 3W 10-ohm resistor takes care of the current limiting for the front panel display. Luckily the backlight and the display itself run off of two differed power lines so I pulled out the 10-ohm and am going to put a 390 in its place... That should drop the v to what I need give or take since I'm putting three LED's instead of the original two lamps.

That's where I'm at now... I'm off to the store to pick up the resistors and LEDs and will do the mod tonight.

I'll keep everyone posted.

you can just replace the 24v lamps with the soldering iron and a beer but they're just going to burn out again.

The resisitor that controls the 24v is just in front of the 2-pin connector near the rear left of the main board. The resistor is hard to miss... It's the big one with insullating fabric tubing on each of the exposed leads.

You have to remove the two screws from the mainboard on the right, the retaining clips on the left and the screw between the RCA jacks on the back panel. You should be able to pop it out with a little gusto.

Desolder the big resisitor and replace it with a 390-ohm 2W. You can then replace the lamps with LED's. This calculation was based on three blue LEDs. The value will change a little bit depeding on if you want to use just two LEDs or a different color as different LED's have a different forward voltage but at a 24v supply just about every color with just use a 390-ohm.

Good luck and let me know how it goes. I still havent gotten to the electronics store. Probably monday.

All done!

Ended up using a 330-ohm 2W resisitor as I chose blue LED's which use a higher draw and not as much resistance is required. Do your own math if you chose other colors.

Also I found that the LED's create spots of light. I diffused them by giving each LED a light sanding with 300-grit sandpaper. But you could just buy diffused LED's... I had already installed the clear ones so I couldn't return them obviously. Just a hint.

I also purchased 2500mcd LED's which is just bright enough. If you want something that is readable from across the room.... Go brighter than that.

I just came across this post. I have the same problem. The CD works but the display has gone blank. I have some photos of the inside of my NAD 510. I thought it may help others if I posted them here. I highlted what I think is the resistor. I'd be 90% sure. I have no experience doing electronics like this though.




Well I hope this helps. Oh yeah, I almost forgot there is a video (in Danish?) with english subtitles that uses a different method of adding the resistor onto the LED circuit. Its available here on Google video Its quite interesting.

Anybody have or know where I could get a copy of the NAD 510 service manual?

I'd love to know the formula jasonlaronde used to calculate the resistor strength for his fix.
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Looks like the correct one from the description.

Calculating resistor values for LED's is just ohms law.

You need to know the supply voltage and the number of LED's in series and the type (colour) of LED.
Red is around 1.7volts, other colours around 2.1 volts and blue and white around 4 to 5 volts

e.g. 6 Red LED's on 24 volts. A red LED drops around 1.7 ?

So the resistor has to drop 24-(1.7*6) which is 13.8 volts.
Next decide what current you want to run the LED's at. It will always be less than 30 to 50 milliamps. If you are running at these current's consult the appropriate data sheet for absolute max ratings. The good news is most LED's are bright on far less so lets settle on 10 milliamp.

The resistor is R=V/I which is 13.8/0.010 giving 1380 ohms... nearest preferred value 1.2k.

Wattage is V squared/R giving 13.8*13.8/1380 which is 0.138 watts. A 0.25 watt or higher would be chosen.

Note... using 1200 ohms changes the current slightly... I'll let you work it out :)

It's all very non critical... and so much depends on what level of brightness you want.

Question ;)
Is the supply to the LED's DC or is it AC. If AC then LED's will perceptibly flicker and also a diode should be added for reverse voltage protection. The resistor value will also be different.
Mooly, thanks for the reply.

Ohms law. That rings a bell- should have paid more attention in double physics all those years ago. I'll have to investigate that some more.

I don't have a multi-meter so this is going to be fun.

I am hoping/presuming that jasonlaronde's 24v will be the same for me even though his mains supply is probably 120v 60Hz and mine is 230v 50Hz

Why is your result 1380 ohms and jasonlaronde's was 390ohm? Is it due to the blue LED's he chose? As some one who hasn't got a clue about this it seems a big difference.

And the question is it AC or DC was also on my mind. I thought it would be DC but having watched this video about a NAD 522 at 2min 20 sec the guy attaches a multi-meter and mentions 4.2v in "dc mode". However at 3min 02sec he attaches an oscilloscope and says that its AC. He goes on from there to attach a rectifier to stop the LED twinkling. So I guess it is AC?

It gives me a lot of hope when you say "It's all very non critical... and so much depends on what level of brightness you want." I don't really care about the brightness , so long as I can read the display. My main concern is I don't want it catching fire or anything like that.
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