CR-2020 faulty 20V power LED: solution possible or donor unit required?

[Oilmaster]

Well I am completing an ultra deep rebuild of a CR-2020 (a rebuild thread will be posted later this year) and finally powered up the unit last night. All working and adjusting just fine, discovering that the POWER LED is not working while the required 20V is across it as it should be.

So, does anybody know if there is more to it like a build-in resistor or zener diode?

And ultimately.... would anybody have a spare laying around from a donor unit?
They must have been used in other Yamaha gear of that era.

It's the left one in the photo, but they are all the same.

 

[dr*audio]

There has to be a resistor in series with the LED to drop the voltage to 3V. Check that first, but LEDs can go bad. Any LED will work. Too bad there are no more Radio Shacks. Digikey has lots of LEDs and if you choose USPS ground shipping, the shipping will be 2 or 3 dollars.

 

[avionic]

http://www.futurlec.com/LED/Red_2mm_LED.shtml

 

[Oilmaster]

http://www.futurlec.com/LED/Red_2mm_LED.shtml

That may work, I'll get some, thanks !

@ dr*audio: yes, I'll strip her down later today to see if it is a faulty internal resistor or something.
But a new one has to be a thin pinhole shape one like avionic's link.

Since this LED has a dedicated output from the PSU control board across a resistor, it will be easy to increase that resistor value to achieve the desired voltage and current to make it as bright (dim) as the adjacent original ones. With some luck a pot may even fit.

 

[Oilmaster]

Well, stripped her down.
Various cracks in the plastic casing, no sign of additional resistors (at least not outside the molded body)
So, just did put an order out for 50 pieces with futurelec as per Avionic's link.

thanks Avionic

 

[avionic]

Hope they work ..

 

[faber12]

Has to be one there somewhere, or else the supply has an issue. LEDs run at 3v, as I am sure you know.

 

[Oilmaster]

Has to be one there somewhere, or else the supply has an issue. LEDs run at 3v, as I am sure you know.

Yes I know all to well

So, I dug a little deeper, and only by magnifying the circuit diagram by 10x ....... it became clear that they printed 2,0 (in orange at PL connection, see below)
My fault

In addition I made a Vf-If curve as attached of an adjacent working LED, and it draws around 11mA at 2.0V
I will add the Vf-If curve of the new LEDs when they come in, but the data provided on the website says 'typical' 1.8V at 20mA, so R740 may need some adjustment.
But that will have to be judged as a function of brightness compared with the original ones.

 

[Oilmaster]

Some close zoom photo of the LED
The faulty LED has cracks throughout the moulded plastic, age fatique it seems.
But in fact, all LEDs have those cracks.... perhaps I better replace all of them.
The power LED certainly makes the most active hours, but the I think it's more a matter of plastic aging.

 

[amr2]

Maybe it's better to change them all.

 

[avionic]

I have a 2020 here thats been waiting for a long time for a once over. Made a note of this to remind me. When I finally "getaroundtoit".

 

[Oilmaster]

Look what I found !!!
100% sub !!

http://nl.farnell.com/multicomp/mcl223md/led-2mm-60-he-red/dp/1581105

 

[amr2]

Nice!!! They are equal!

 

[Vint Age]

Excellent!

 

[Oilmaster]

Ordered 100 red pcs, and 50 green ones as well, with the kind help of Mr. Yamaha
That should do for some years to come

 

[avionic]

Newark Electronics (Element14 USA) only has 3 in stock.

 

[Oilmaster]

Yes, luckily in this case we are located on the other side of the big pool where larger stocks of these LEDs are kept by Element14/Farnell.
No problem to share some in case of urgent needs.
Thinking of it, I could have initiated a group buy here.

 

[rottalpha]

Look what I found !!!
100% sub !!

http://nl.farnell.com/multicomp/mcl223md/led-2mm-60-he-red/dp/1581105

so the last piece of the puzzle is in

Nice happy-ending!

Would we see a detailed rebuild thread on this CR?

 

[restorer-john]

Very cool 2mm LED bookmarked both options.

I've put 5mm in a drill chuck, spun them and filed the front section epoxy down to 2mm in a pinch before. Works well for one offs.

 

[Oilmaster]

Would we see a detailed rebuild thread on this CR?

Really intend to do so later this year; sooooo busy.....