I’m trying to figure out why the CFAX LCD I have is so hard to see. The backlight is very, very dim. I’ve tried two different displays and carrier boards (my first carrier didn’t work at all, and I have since determined that it’s just wrong).
One thing I discovered is that the backlight driver circuit is putting out a 200 Hz wave, not a 400 - 1 kHz wave, which is what the CFAX LCD data sheet says is necessary. I don’t know if that’s part of the problem. The output voltage is around 75 V, so that seems right.
Here’s what I see on the scope, with Orange connected to the top lead, blue on the bottom, and red is the difference. The measured frequency shown is off because of the little spike following each high portion. The first time I did this, I had a very clean square wave on both terminals; I can’t figure out what’s causing this mess. But when it was clean, it measured 201 Hz.
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In any case, you can barely tell the backlight is even on.
(And WhyTF is my image not showing up in the post?)](http://roderickmann.org/stuff/CFAXDriverWaveform.bmp)