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math7 · 09-05-2018, 07:20 AM

Hi, I got this HP 19bii, but it has this spot on the display, apparently it does not have to do with the numbers, because by varying the brightness of the screen with the ON key and + or - the numbers can be read or varied the angle of vision. But it is somewhat annoying and can not be read quickly in low light or if they have many digits. Does anyone know why a stain is made like this and how could it be removed?

Maximilian Hohmann · 09-05-2018, 04:09 PM

(09-05-2018 07:20 AM)math7 Wrote: Does anyone know why a stain is made like this and how could it be removed?

Guessing from the photos to me it looks like the residue of some liquid, maybe just condensed water, trapped either between the LCD and the protective layer of clear plastic, or between the glass of the LCD and the polarising filter.

In any case the calculator would need to be disassembled to clean it out which is not an easy thing to do and which carries a big risk of inflicting major damage.

If you are very lucky the stain was caused by someone who cleaned the screen with some kind of solvent and left it to dry in a puddle instead of wiping it off. In that case it might be possible to even it out somewhat with more solvent (start with "gentle" ones like alcohol and lighter fuel before moving to hard stuff like paint thinner and acetone!). Or try to polish it out with a mild polishing paste like "PolyWatch". I wouldn't waste to much time on it, these calculators are in plentiful supply and not as expensive as others from HP. I bought one a couple of weeks ago in near mint condition for 10 Euros.

Regards
Max

math7 · 09-05-2018, 05:34 PM

I cleaned with a little alcohol but the stain seems to be below the display not above. In case of having to open, how is this calculator disarmed? Does it have screws in part or is it opened by the hinge it has? Any ideas? Could heat be used from a hot air gun?

Maximilian Hohmann · (This post was last modified: 09-05-2018 05:52 PM by Maximilian Hohmann.)

(09-05-2018 05:34 PM)math7 Wrote: In case of having to open, how is this calculator disarmed? Does it have screws in part or is it opened by the hinge it has?

No screws, unfortunately. Here is a description about how to open an HP-28:
http://www.hpmuseum.org/cgi-sys/cgiwrap/...ead=185173
The HP-19 should be very similar apart from a slightly different position of the heatstakes. Opening it is one thing, getting it back together and restoring a decent look is another thing!

PS: Here is another instruction with even more photos: https://www.teawea.com/how-to-open-a-hp-28s-calculator/

math7 · 09-05-2018, 07:07 PM

Thank you very much Maximiliam for the links, you went to study them to dare to disarm my HP 19, because the truth I got it cheap at 10 dollars but I have seen others on the internet and it costs more than that, and the truth is that I got the keyboard and covers in very good condition, I think it's worth trying to repair that stain on the screen, and I hope the stain can be removed and not sea as the display ink

Zaphod · (This post was last modified: 09-05-2018 07:25 PM by Zaphod.)

By the way, the word is disassembled , not disarmed Smile

It looks like maybe glue residue from a sticker ?

I can’t see that being in any of the internal layers ..... if it’s not on the outside surface forget trying to open up the screen (you will destroy it) , find a donor machine as suggested.

Robert VM · (This post was last modified: 09-05-2018 07:28 PM by Robert VM.)

May be the adhesive of the reflective surface or the polariser at the back of the display.
Perhaps it's been in the sun for too long?

Good luck!

burkhard · 09-05-2018, 07:55 PM

There's an active thread just (at the moment) near this one entitled "HP-28S battery door".
If you go into that thread, there's a gentlemen in Brazil who repairs HP calculators.

Take a look at his "before and after" pictures with center spots on the displays of a 42S and a 32SII that look similar to that on your 19BII:

http://hpcenter.com.br/fotos.html

I expect paying for such a repair isn't worth it for a 19BII, but the trouble does look similar.
If it were too annoying to live with, I would use it as a learning experience in fixing clamshell calculators.

math7 · 09-06-2018, 02:30 AM

(09-05-2018 07:28 PM)Robert VM Wrote: May be the adhesive of the reflective surface or the polariser at the back of the display.
Perhaps it's been in the sun for too long?

Good luck!

Actually I do not know why I bought it in the business that had it on display. I do not know if it fell and hit some time, but you can see that it is below the display, what I do not know is if this is a plastic protector or is the same display or there is another layer below, I was thinking about applying heat with a gun of heat to see what happens.

burkhard · 09-06-2018, 03:11 AM

(09-06-2018 02:30 AM)math7 Wrote: Actually I do not know why I bought it in the business that had it on display. I do not know if it fell and hit some time, but you can see that it is below the display, what I do not know is if this is a plastic protector or is the same display or there is another layer below, I was thinking about applying heat with a gun of heat to see what happens.

I'm not certain how the display is constructed, but in one of your pics I can see the crack in the lower right corner of the display bezel. I have a 19BII (a rear door one, no less!) that is otherwise perfect, but has this exact same bezel crack in the same place. I intend to carefully fix it with clear 3 minute epoxy, but haven't done so yet.

The plastic they used on the clamshell cases is evidently on the brittle side.

math7 · 09-06-2018, 04:34 AM

(09-05-2018 07:55 PM)burkhard Wrote: There's an active thread just (at the moment) near this one entitled "HP-28S battery door".
If you go into that thread, there's a gentlemen in Brazil who repairs HP calculators.

Take a look at his "before and after" pictures with center spots on the displays of a 42S and a 32SII that look similar to that on your 19BII:

http://hpcenter.com.br/fotos.html

Excellent and thanks for the information. I think the arrangement would be more expensive than what I paid for the calculator. But if this person fixes the displays, I wonder what methods can be used for that, and do it yourself as a learning and so the cost of repair is not so high?

burkhard · 09-06-2018, 01:10 PM

(09-06-2018 04:34 AM)math7 Wrote: Excellent and thanks for the information. I think the arrangement would be more expensive than what I paid for the calculator. But if this person fixes the displays, I wonder what methods can be used for that, and do it yourself as a learning and so the cost of repair is not so high?

That's kinda what I was thinking. I'm not sure if his fix is an outright replacement of the display or something else. The 19BII isn't particularly valuable, and yours looks like it's got some side battery door problems as well, so it would be a good one for you to learn / experiment on if you enjoy such things.

mfleming · 09-06-2018, 09:53 PM

(09-05-2018 07:28 PM)Robert VM Wrote: May be the adhesive of the reflective surface or the polariser at the back of the display.
Perhaps it's been in the sun for too long?

Good luck!

This reminded me of an earlier thread where a fix for a bad display like you have was posted. Unfortunately, gaining access to the display for such a repair sounds like a difficult task...

~Mark

math7 · 09-09-2018, 11:22 PM

Thanks mfleming I already saw the link that you mentioned, and if the problem is that it is a bit difficult to open the calculator and close it and make it look good.

teenix · 09-10-2018, 02:29 AM

Maybe left in bright sunlight??

I've seen this can turn LCD's black. Not sure if its the UV or the heat that causes it. The case doesn't look heat warped though.

cheers

Tony