Fixing the Naim NADI and Mains switch

[colasblue]

Yesterday I got bored enough the have a go at properly repairing the NADI in one of my 135's which blew a couple of diodes a few month ago. I'd previously fixed it temporarily by substituting a couple of 220R resistors in place of the dead LED units which worked fairly well but resulted in it being a little dim.

In fairness I had to open it up anyway because the switch wasn't latching properly. I had bought a Chinese replacement switch but unfortunately it didn't quite fit the space. Fortunately all that was wrong with the original is that the spring had become weak over time so I was able to transplant the spring from my incorrect replacement and fix the problem. Easy job - no soldering required. Surprised we don't hear a bit more about it.

NADI not so easy. The original dual LED unit from Kingbright is now unobtanium.

https://uk.farnell.com/kingbright/ka-9219-2sgc/led-9-2mm-green-35mcd-568nm/dp/2373363?ICID=I-HP-STM7REC-RP-1

I found these axial LED's on ebay

369/10#LED axial 1,8mm vert 570nm 10pcs | eBay

Lot de 10 LED axial vert 570nm (vert /jaune). Vert/Jaune 570nm. Référence 369. Vert 530nm. Jaune 590nm. Blanc 7000K. Bleu 470nm. Jaune 588nm.

www.ebay.co.uk

and by joining a couple of them together fabricated a dual LED unit which could replace the Kingbright one.

I was a bit worried that the new ones might be much brighter than the originals, which have had 34 years to "droop" but actually they worked really well and I needn't have worried.

 

[nuclear_jimbo]

How does the colour match? It's been a job that's on my to-do list for a while.

 

[colasblue]

Perfectly! That's the one thing you actually can guarantee due to the properties of solid state physics. Any 570nm green LED should be the correct colour.

The difficult one is brightness and I think I got really lucky with that. I would have been less lucky if I'd been fixing a newer brighter NADI.

 

[hp1]

The later Nadi just had a lower value dropper resistor so appears brighter , it was also a lot less reliable .
I increase the value of the dropper resistor on all mine to preserve the leds ,I think they are now 4k7 and never had an led fail.

 

[colasblue]

That definitely isn't the whole story. LED's have also improved in efficiency over the years and older ones "droop" ie get dimmer as time passes.

This used to be is entirely obvious just by looking at one of my other pairs of 135's (made in 1990) . One NADI had been replaced entirely in the late 2010's and the other was original. Both had the same 1K drop resistor but the newer one was much brighter.

I eventually swapped the overly bright one for the one on my Supercap made in 1996, and the difference was much less.

I'm sure I could better match them still by swapping over one row of the LED's from one to the other, but there's always the risk of damaging one on extraction so I haven't gone there.

It's also obvious to anybody who owns an 82 or 52 since the record function LED's where the selector is usually "parked" are usually a great deal dimmer than any of the others.

 

[The_JJ]

I been looking a rectangular backlight that is close enough to the right size, no luck so far