HP-48GX black and white screen: blue indicators?

[Dave Dirckx]

    Hello,

I already own an HP-48S and HP-48G and finally found an HP-48GX on eBay with a black and white screen which is indeed much clearer for me than the blue and green. I'm glad with it because the calculator is in a very good condition.

But I've remarked one thing that was a bit surprising to me: the status indicators (shift indicators, hourglass) on the top of the screen are still blue... Is this normal? I'm a bit surprised this is the case, I would expect that a LCD screen would be all with black pixels.

In fact nothing to worry about, but I wanted to ask it to the specialists here or other owners to confirm it. Thanks!

[Gerson W. Barbosa]

Same here, except for the dark spot in the center of the screen in mine :-(

[Lithium]

Yep normal, don't know why but I guess the screen on the late 48GX is identical to the 49G screen, and these screens have blue indicators. Surprising at first

[Dave Dirckx]

Thx for confirming. Bizarre my display is not so greenish and there's more bezel on the left and right on Gersons HP-48GX. Either way, it looks that those indicators were blue on all GX with the black pixel display...
   

[Lithium]

These were the screens on late Indonesian made GX. My Gx's don't have black pixels LCD but my 49G's screen look exactly like yours. I suspect the light/camera color balance on Gerson's pic is a bit off too. As for the"leftover" space on the left and right, I'll have to examine my 48/49 to confirm.

[cyrille de brébisson]

Hello,

My understanding is that the screen (pixel area) is multiplexed. Each row/pixel only gets energized for 1/64 of the time. Bump up the contrast (which bumps up the voltage), especially past the software forced limit (by writing in the IO rom directly using the POKE command), and you will see that the screen pixels will become blue-er, which is their saturated color...

Now, the Indicators are NOT multiplexed, they are energized 100% of the time. So they show as the other pixels would if they were fully energized.

Cyrille.

[damaltor]

You are right with that assumption. The main display area is multiplexed, so each pixel is enabled only shortly, while the annunciators are non-multiplexed and are 100% energized. This has some interesting side-effects, and one of them is the blueish colour.