Vintage Synth Repair

Russ,

Thanks for confirming. I pulled one end of the resistor, it is an 8.2 
ohm. Leaving that disconnected upon powerup the display had graphics 
but ZERO backlight. Monday I'll pick up a couple of resistors from 
work to try, or maybe a pot so I can adjust the brightness I want. 
I'll let you know how it goes.

Thanks again, Synthflake

--- In vintagesynthrepair@yahoogroups.com, Russ Rose <russrose@m...> 
wrote:
> on 3/26/05 10:10 AM, synthflake at gemjamstudio@h... wrote:
> 
> > 
> > 
> > Ok, a closer look at the display and the backlight is working, 
just
> > not nearly as bright as my Korg 03R/W and Yamaha TG500. Roland 
told
> > me the $115 LCD is now discontinued and telesisbacklighting.com 
says
> > they can't fix those but wanted me to check to make sure I was
> > driving enough current for the backlight. Looking inside the unit
> > there is a 1/4watt resister (axial) right next to the header where
> > the LCD ribbon cable plugs in, I'm wondering if this may be a 
current
> > limiter for the LCD backlight? Seems logical that in a mass of SMT
> > devices a single precision 1/4 watter right next to the 
connector...
> > Does anyone have a schematic of the JV880 that might show a LCD
> > backlight intensity select resistor?
> > 
> > Synthflake
> 
> Okay. I have a schematic( or as some of my customers call a sketch-
0-matic)
> There is a resistor designated R116, one end tied to Vcc(+5 volt 
dc) and
> the other tied to pin15 of the ribbon cable to the LCD. The 
schematic does
> not give the
> value(thanks, Roland). Get this, neither does the parts 
list, "describing"
> R116 on main board, ERD2FCJ8R2P. I am guessing the value to be 8.2 
ohms.
> So should be easy enough to measure the value of the resistor you 
found.
> If the display has only this one 16pin ribbon cable and also not a 
separate
> 2 conductor cable , chances are good that the backlight is not a EL 
type
> but a LED type. Given this, pin 15 is where the LED's get their 
current.
> To positively determine this, try lifting one end of R116; if the 
backlight
> disappears, then that's it. Now then, brother, you are on your own 
if
> want to change the value of it. If you do change it, advise 
conservative
> value to 7.5 or 6.8 ohms. Also keep in mind that I deconstructed
(guessed)
> the value based on the part's list description, better yet to 
determine
> the value by the color code. Good Luck. Russ