[sdiy] LEDs dying in LCD alphanumeric display

[Olivier Gillet]

If you want to replace a 2x16 module by something:
- thiner than the usual LED backlit LCD (by 4 or 5mm)
- that doesn't require the adjustment of a backlight resistor (pin 15
/ 16 of the module are left unconnected)
- that doesn't require contrast adjustment (pin 3 of the module unconnected)
- super crisp, no matter the viewing angle

-> New Haven 2x16 characters OLED modules, HD44780 compatible. Mouser
763-NHD-0216KZW-AB5 for example.

On Sun, Nov 6, 2011 at 10:34 PM, J.D. McEachin <jdm at synthcom.com> wrote:
> On 6 Nov 2011, at 03:43, Adam Inglis wrote:
>
>> 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.
>
> It's remarkable how electronics manufactured at the same time can reach
> end-of-life within weeks or even days of each other.
>
> It's odd that the LEDs would die, though, unless the unit has been left on
> for many years, or the LEDs were overdriven.
>
>
>>  The LCD works and responds to
>> contrast control.
>
> The contrast control has nothing to do with the lighting.
>
>
>> 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
>
> But which one - edge LED, SMD LED, or EL?  Big differences...
>
>
>> Can you crack these open and replace the LEDs or do you replace the
>> whole unit?
>
> Maybe.  But I find it easier to just replace the unit.  Especially when the
> same model is available.
>
> I've now replaced almost all the LCDs in my studio.  I started the project
> because my EL backlights were failing.  Then I decided that I hated the
> putrid yellowish-green LCDs that most studio gear sports, so I started
> changing out working LCDs so the colors matched the gear's paint scheme.
>  Call me crazy for spending the time & money; I laugh at myself about it
> sometimes.  :)  Here are some tips:
>
> * Pretty much all character LCDs are compatible with the Hitachi HD44780
> controller.  So far I haven't found any 80s gear that won't work with the
> CrystalFontz and Matrix Orbital LCDs I've been using.
>
> * If the original display isn't available (or wanted), ALWAYS open the gear
> up and take some measurements before selecting a replacement LCD.
>
> * LCDs w/ LED backlights are almost always thicker than the ones w/ ELs.
>  Usually this can be accommodated by changing out the standoffs or bending
> the mounting tabs, but sometimes requires more radical surgery.  The worst
> was my Prophet VS rack - I had to partially cut the pcb and let it flex back
> to get the .5mm clearance needed (it's ugly on the inside, but beautiful on
> the outside).
>
> * Make sure the LCD is the right size for the window on the front panel.
>
> * If the contrast circuit has a panel-mounted pot, it will probably work
> just fine.  If it's a fixed resistor, probably not.  If it's a
> CPU-controlled PWM circuit, forget it.  For the latter 2 cases, I've been
> drilling a hole in the back panel and mounting a potentiometer so the VO
> voltage (pin 3) can be adjusted.
>
> * If there's a high voltage inverter for the old EL backlight, this is a
> great opportunity to remove it and get rid of a potential noise source.
>
> * Make sure you get the current-limiting resistor for the LEDs right!  I
> usually calculate the value according to the datasheet, insert a trim pot in
> the circuit, and dial up the resistance until I can see the display is
> getting dimmer, then back off a little until it's back to full brightness.
>  There's usually no need to run at max current, and it will increase the LED
> life.
>
> Hope this helps.  Good luck with your repair!
>
> Jeffrey
>
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>