Weak Backlight - Riovolution

shish

2008-09-30, 11:18 #1

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Subject: Weak Backlight

after modding my karma with a new 2200mah battery and a 16gb CF card i've started to notice the backlight is a bit weak. Not sure if this is something thats happend recently or over time since i bought it (have owned mine from new since they were released).

Wondering if anyone has modded a led backlight onto a karma and / or knows anything about the switching circuit that would allow me to disable the EL backlight inverter and switch a couple of white leds instead

straycat 2008-10-07, 09:54 #2

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Member since Aug 2008 · 37 posts · Location: Portugal
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i know it's normal for the backlight to start fading over time.
i have 2 karmas and my oldest is getting so dark, i have to turn on the lights to read the screen at night or look at it really close.

shish

2008-10-07, 14:18 #3

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yea i guess i was just hopeing it wasn't just dimming, i dont think i really used it enough to expect it to fade so much.

I did try and measure the voltage on the backlight element when i was last in there and found it to be actually quite low, so i'm wondering if something is actually failing in the driver circuit as i only measured about 75v, i expected something in the region of 100+ volts

John30_06 2008-10-07, 21:05 #4

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I saw a guy a while back selling an LCD on ebay made by a 3rd party that would interchange with a Karma. I really should have bookmarked that.
The only option I see is to watch ebay for parting-out units, unless one of the former Engineers would be able to divulge where they came from originally, and whether they could be bought retail.

shish

2008-10-08, 01:54 #5

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i've just ordered a generic EL panel off ebay which can be cut to size, so i'll try it and see if it works. Will let you know if it does.

ukre 2008-12-07, 00:18 #6

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In reply to post #3

It's probably not the driver, this shouldn't degrade; the EL panel will though - the only solution is a new panel. Careful though - you can get a little bite from the driver...

Replacing the EL with LED isn't easy as you need a light spreader; there is actually quite a decent amount of room under the panel though, so if you found another display of about the right size it should be possible to trim the spreader to size and put it under the display. You'd need to add a white LED boost to drive the LEDs (eg the LT3200 from linear tech) but this shouldn't be too hard. One end of R169 is the backlight on signal (active high).

shish

2008-12-07, 04:50 #7

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hi ukre, thanks for the reply (i assume your the original ukre from the old forums?)

i do have a 'generic' el panel here i bought of ebay, i'm intending to cut this down to fit in place of the original one, which will hopefully work.

Special thanks though to the info about the backlight signal line, this is perfect and i'll certainly look into a led conversion now. Old 320x200 pda screens should be perfect for dissecting out the backlight/diffuser.

top stuff, thanks! ;-)