LCD Backlight Question(s)

[BraveNovice?]

Newbie here :-)

I have an older '90s BOSS SE-50 multi-effects unit. Years back on an overseas tour it accidentally got plugged into a 220 line - yikes! Blew up the power supply line lump, easily replaced - and the unit works fine, with the exception that the LCD display backlight went kaput. The LCD is fine otherwise, just no light.

I'm wondering what to look for, component-wise, that blew out that creates the backlighting. (I have an Alesis module - S4 - that uses a row of LEDs, but can't see any such light source for the BOSS. The display looks identical to the one in my Roland U-110 PCM sound module.

Any insights are appreciated. THANKS

[Enzo]

In which case it would perhaps be an electro-luminescent panel. The whole thing glows itself, like those pale blue glowing discs used as night lights in a bedroom.

Usually those run on a higher voltage from a small DC/DC converter module. Look for a smallish metalic cube at the other end of a pair of wires from the panel.

Any chance you can link us a schematic?

[Jon Snell]

I would look for an open circuit 12volt mini lamp alongside the display inside. The lamp is before the regulator and will blow quickly if 12volts is exceeded.
Available from RS, Farnell, Mouser, DigiKey, ebay etc.

[doctor]

Voltage of 9VDC is used for backlight of this display.

First of all check voltage 9VDC on connector CN3: pin 1 – 9VDC, pin 2 - GND.
If this voltage is absent, check R42 (68 ohm /1W), R43 (22 ohm /0.2W)
and D3 (Zener diode 9.1V/0.5W).
If some part is out of order, replace it. Pay attention on the diode polarity.

If this voltage presents, the backlight is out of order.

Now you have 2 options:

1. You can use few LEDs or mini lamps as Jon offered.

2. You can use new LCD having its own backlight.
LCD must have suitable dimensions and interface.
The original interface is standard.
Here it is on the connector CN4:
1-VDD (+5V)
2-VSS (GND)
3-RS
4-VO
5-E
6-R/W
7-D1
8-D0
9-D3
10-D2
11-D5
12-D4
13-D7
14-D6

[oc disorder]

Manual Here
http://www.warningwillrobinson.com.a...e%20manual.pdf

Info re backlight from manual on this jpg

[g1]

What that backlight info sheet is basically saying is that the backlight problem is not serviced. If the 9V is being sent to the module, then they replace the whole LCD module.
If you want to try to repair the module, you are on your own. Sometimes it is possible, but not always.