HP 48GX screen contrast

[groskwik]

I often go to this forum but I realize this is my very first post !

The HP-48 GX is still for me one of the best calculator ever made. I've just bought another one for almost nothing in an amazing condition. So I have two GX. One is a 1996 revison R and one is a 1993 revision P (the "new" one).

I immediately saw two differences between these units :
- The screen of the rev. P as a better contrast.
- The color of the rev. P is more matte than the rev. R.

What surprises me more is the screen contrast. Why is it better on the older one ?
In the attached picture you can see the difference (even if it is easiest to see in real). If I press [On] [-] on the Rev R to lighten the background at the same level as the rev. P, the letters start to "disappear".

[damaltor]

The revesion only represents changes in the software ROM, not in the hardware. it somewhat correlates though as later units have later roms. here you can see the three display that were used throughout the time:



The slight differences of your display are probably tolerances of a single display variant.

If the 48 were not so unbelieveably slow, i would use it every day...

[RMollov]

(08-31-2016 10:15 AM)damaltor Wrote:  If the 48 were not so unbelieveably slow, i would use it every day...

Slow by today's standards maybe. Speed was never a problem when they came around unless used for 'graphicking' etc. IMO still the best - the ones with b/w display.

[Raymond Del Tondo]

(08-31-2016 10:15 AM)damaltor Wrote:  The revesion only represents changes in the software ROM, not in the hardware. it somewhat correlates though as later units have later roms. here you can see the three display that were used throughout the time:



The slight differences of your display are probably tolerances of a single display variant.

If the 48 were not so unbelieveably slow, i would use it every day...

A small addition: The GX in the middle has an SX LCD, the one on the left has a normal GX LCD, and the one on the right has the high contrast LCD.
I put the unit equipped with an SX LCD in the middle because even there, it has the worst readability. If I placed it one the left side, the LCD would have been next to unreadable.

I'd recommend getting a GX with high contrast LCD as long as someone offers them. The prices are high (like the contrast) but it's worth the effort if you really want to use the HP 48:-)

[Paul Berger (Canada)]

If you are brave and want to swap out the display 39G or 49G can be a low cost source of a grey screen that will work fine in a 48GX, and for that matter in a 48SX I would suppose.

[groskwik]

(08-31-2016 10:15 AM)damaltor Wrote:  The revesion only represents changes in the software ROM, not in the hardware. it somewhat correlates though as later units have later roms. here you can see the three display that were used throughout the time:



The slight differences of your display are probably tolerances of a single display variant.

If the 48 were not so unbelieveably slow, i would use it every day...

Yes I know the rom revison has no relationship with lcd. It was a convenient way to name these two GX. In your pictures these are three differents LCD hardware. My two LCD are supposed be the same. Yes It must be a tolerance problem.

[Han]

(08-31-2016 07:45 PM)Paul Berger (Canada) Wrote:  If you are brave and want to swap out the display 39G or 49G can be a low cost source of a grey screen that will work fine in a 48GX, and for that matter in a 48SX I would suppose.

Here's one: http://users.ju.edu/hduong/repair/repaired1.jpg

[rprosperi]

(08-31-2016 09:31 PM)Han Wrote:  Here's one: http://users.ju.edu/hduong/repair/repaired1.jpg

Wow, what a dramatically better looking machine the 48SX is with Black LCD! It's surprising that this seemingly simple change can have such a big impact on it's appearance.

But you see, Han, now you've gone and done it! I want one.

Thanks for sharing that.

So any 48GX (black), 39G or 49G LCD can be a donor? Gotta look through the parts boxes....

[DavidM]

(08-31-2016 09:31 PM)Han Wrote:  

(08-31-2016 07:45 PM)Paul Berger (Canada) Wrote:  If you are brave and want to swap out the display 39G or 49G can be a low cost source of a grey screen that will work fine in a 48GX, and for that matter in a 48SX I would suppose.

Here's one: http://users.ju.edu/hduong/repair/repaired1.jpg

Oh, you two have done it now. My 48sx with a bad display is now shouting at me to find a donor system with a black LCD. But I just have this sinking feeling that if I actually go through with the process, I'll end up screwing up my keyboard. Or having a display with even more problems. Or who knows what other mischief I'll step into.

[Han]

(09-01-2016 01:05 AM)DavidM Wrote:  

(08-31-2016 09:31 PM)Han Wrote:  Here's one: http://users.ju.edu/hduong/repair/repaired1.jpg

Oh, you two have done it now. My 48sx with a bad display is now shouting at me to find a donor system with a black LCD. But I just have this sinking feeling that if I actually go through with the process, I'll end up screwing up my keyboard. Or having a display with even more problems. Or who knows what other mischief I'll step into.

I have found that in almost all HP48's that I have opened the rubber piece pushing the keyboard contacts onto the pcb has decayed to some degree. Even if all keys work properly, I generally just go ahead and place another piece of foam behind it to help push the contacts even closer for good measure.

I have found that the 39G to be the most economical donors.

[DavidM]

(09-01-2016 01:39 AM)Han Wrote:  I have found that in almost all HP48's that I have opened the rubber piece pushing the keyboard contacts onto the pcb has decayed to some degree. Even if all keys work properly, I generally just go ahead and place another piece of foam behind it to help push the contacts even closer for good measure.

I have found that the 39G to be the most economical donors.

What type of foam do you use? And how do you obtain it?

Also, I could be dreaming but I seem to remember that something I've seen (maybe even your own online instructions) mentions that there are at least two different kinds of display connectors on the 48 systems. Is there a way to know before opening if the displays are interchangeable? I'd hate to start down this path only to find that the display replacement isn't possible.

[rprosperi]

(09-01-2016 01:39 AM)Han Wrote:  I have found that the 39G to be the most economical donors.

Yessir! Just found one for $14, shipped. Sometimes it's a good thing that some of these HP machines didn't fare so well in the market, or at least not for long.

[Han]

(09-01-2016 01:53 AM)DavidM Wrote:  

(09-01-2016 01:39 AM)Han Wrote:  I have found that in almost all HP48's that I have opened the rubber piece pushing the keyboard contacts onto the pcb has decayed to some degree. Even if all keys work properly, I generally just go ahead and place another piece of foam behind it to help push the contacts even closer for good measure.

I have found that the 39G to be the most economical donors.

What type of foam do you use? And how do you obtain it?

Also, I could be dreaming but I seem to remember that something I've seen (maybe even your own online instructions) mentions that there are at least two different kinds of display connectors on the 48 systems. Is there a way to know before opening if the displays are interchangeable? I'd hate to start down this path only to find that the display replacement isn't possible.

I don't remember the specific type of foam, but it was essentially a very thin foam tape (yet thick enough) that I cut into the right size. (It resembles this: https://signobi.com/internalProducts/foa...m-tape.jpg)

And yes, the connectors for the screen (they look like rubber strips) are specific to that screen. It may be that two screens can interchange the connectors, but in general the grooves in which the connectors sit are the exact depth for their respective connectors.

[groskwik]

(08-31-2016 09:31 PM)Han Wrote:  

(08-31-2016 07:45 PM)Paul Berger (Canada) Wrote:  If you are brave and want to swap out the display 39G or 49G can be a low cost source of a grey screen that will work fine in a 48GX, and for that matter in a 48SX I would suppose.

Here's one: http://users.ju.edu/hduong/repair/repaired1.jpg

Your SX is amazing !

[Visu]

(08-31-2016 03:13 PM)RMollov Wrote:  

(08-31-2016 10:15 AM)damaltor Wrote:  If the 48 were not so unbelieveably slow, i would use it every day...

Slow by today's standards maybe. Speed was never a problem when they came around unless used for 'graphicking' etc. IMO still the best - the ones with b/w display.

One of the reasons why I use voyagers on a daily basis.

[pgyore]

Does anyone have a DIY link for replacing the LCD in an HP 48SX?

Surely I will get a raise at work. The Vice President uses his everyday; it sits on his desk, next to his keyboard.

I think he has 3 of them. He has no interest in 48G or 50Gs.


Best regards.

*** SOLUTION ***

Ok, about 30 minutes after I requested a link to the DYI, I thought, perhaps that image came from a DYI page. Sure enough..

http://users.ju.edu/hduong/repair/



Best regards.

[Hlib]

(08-31-2016 10:15 AM)damaltor Wrote:  ...The slight differences of your display are probably tolerances of a single display variant. ...

Yes. Super quality of my HP-48gii vs HP-50G is possibly related to "slight differences" in LCD and keyboard? :-)))