[sdiy] LEDs dying in LCD alphanumeric display

[Harry Bissell]

I had a similar failure in an Alesis D4 drum machine. The LCD was backlit by 24 parallel
connected LED chips bonded to a copper (PCB) substrate. Once one chip fails, the others get
progressively higher current and fail more rapidly.

Mine has direct bonded LED dies with bond wires covereed in silicone goo. I removed the goo
AND the bond wires. Cleaned up the board and bought 100 surface mount LED chips. I set a constant
current source to 10mA and measured the forward voltage drop across each one, choosing the 24 that were
closest to each other (iirc ther were less than 50mV apart) and made the repair with these chips.

Failure to match the LEDs is a guarantee that they will burn out again. The better job you do, the more
long lasting the repair.

It was a major operation but not too difficult, just fussy...

H^) harry


----- Original Message -----
From: MTG <grant at musictechnologiesgroup.com>
To: Adam Inglis <21pointy at tpg.com.au>, synthdiy diy <synth-diy at dropmix.xs4all.nl>
Sent: Sun, 06 Nov 2011 09:39:00 -0500 (EST)
Subject: Re: [sdiy] LEDs dying in LCD alphanumeric display

If you didnt put in current limiting reistance you could be killing it...?

GB
www.musictechnologiesgroup.com


----- Original Message ----- 
From: "Adam Inglis" <21pointy at tpg.com.au>
To: "synthdiy diy" <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, November 05, 2011 7:43 PM
Subject: [sdiy] LEDs dying in LCD alphanumeric display


> Why would the LEDs that backlight my Proteus' 2x16 LCD display slowly  
> die from left to right over the course of a couple of weeks? Seems  
> like an odd failure mode. The LCD works and responds to contrast  
> control. The 5 volt supply for the LED circuit is separate from the  
> LCD supply, but they both measure up fine.
> 
> It's one of these...
> http://www.densitron.com/displays/Alphanumeric_LCD.aspx
> 
> Can you crack these open and replace the LEDs or do you replace the  
> whole unit?
> 
> cheers
> Adam
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
_______________________________________________
Synth-diy mailing list
Synth-diy at dropmix.xs4all.nl
http://dropmix.xs4all.nl/mailman/listinfo/synth-diy

-- 
Harry Bissell & Nora Abdullah 4eva