The Museum of HP Calculators

HP Forum Archive 19

[ Return to Index | Top of Index ]

HP 35s - scratched screen
Message #1 Posted by Matt Schilling on 17 Aug 2010, 2:36 a.m.

I was wondering if anyone has any solutions to repairing scratches to the display of the 35s? Any other information about the type of screen and whether it is a cover would be helpful. I don't want to go trying to fix it and making things worse. Cheers

Re: HP 35s - scratched screen
Message #2 Posted by Thomas Radtke on 17 Aug 2010, 3:17 a.m.,
in response to message #1 by Matt Schilling

There's a plastic cover on top of the LCD in my sample. It can likely be repaired by e.g. Displex. However, I've read in this forum that there were 35s without that cover IIRC, so be careful.

I'd try to replace it with a less reflective material if my 35s were concerned (and were still in use).

Re: HP 35s - scratched screen
Message #3 Posted by Dallas Osborne on 17 Aug 2010, 11:35 a.m.,
in response to message #1 by Matt Schilling

Yup, pop it apart and replace it.

Here you go: HP 35S Screen Replacement/Upgrade (and alignment)

EDIT: I used the plastic LCD cover from an unsuspecting co-workers office phone. (He hasn't noticed yet.)

Edited: 17 Aug 2010, 12:29 p.m.

Re: HP 35s - scratched screen
Message #4 Posted by Bruno Férard on 17 Aug 2010, 2:40 p.m.,
in response to message #3 by Dallas Osborne

Very good tutorial, thanks for sharing. I haven't this problem at the moment, but it can be useful someday...

Re: HP 35s - scratched screen
Message #5 Posted by Matt Schilling on 23 Aug 2010, 2:29 a.m.,
in response to message #3 by Dallas Osborne

Thanks for the help. How do I pop it open? And will it go back together the way it was beforehand?

Re: HP 35s - scratched screen
Message #6 Posted by Jeff O. on 23 Aug 2010, 1:13 p.m.,
in response to message #5 by Matt Schilling

Opening the case is easy. Remove the rubber plugs in the four corners of the battery compartment, then peel off the rubber strip on the bottom of the calculator, and remove the six screws. The front and back halves of the case are also held together by five plastic catches, one in the middle on the top edge, one in the middle on each side, and one near the bottom on each side. These catches are not exceptionally tenacious; some gentle tugging at the case halves and careful prying between them will fairly easily separate the front and back. When re-assembled it should appear is if it has never been opened.

For further information on the internal construction of the 35s, you may wish to review this post of mine from a few years ago when excitement was high over the prospect of repurposing the 35s.


Re: HP 35s - scratched screen
Message #7 Posted by Dallas Osborne on 23 Aug 2010, 2:27 p.m.,
in response to message #6 by Jeff O.


Jeff, I missed your post while I was typing that response.

That is one detailed disassembly!

Re: HP 35s - scratched screen
Message #8 Posted by Dallas Osborne on 23 Aug 2010, 2:23 p.m.,
in response to message #5 by Matt Schilling

Okay… this is the fun part and there are many more experts here. I strongly suggest searching the archives for posts concerning this type of surgery.

Here we go!
Prep the work area.
-Good lighting.
-Serving tray (keep the bits and pieces from making a break for it) -Cellophane tape (the kind that comes off easily without leaving sticky patches)
-Straight edge (ruler)
-Little Philips screw driver
-Double sided tape.
-Plastic something for prying. I use a plastic knife with the end cut off and filed down a bit.
-X-acto knife with a little pointy bit or a sewing needle.
-A wee bit of superglue. (Cyanoacrylate)
-New screen material. This is entirely up to you and I don’t have any good sources to recommend. You will need to look around for something with about the same thickness. Again, I used the LCD cover from a co-workers office phone. He never noticed( and he uses a TI). The material has a nice matt finish.
-Lots of time. Working under pressure, such as before the spouse comes back and finds you at the table with a naked… calculator, is not good. Some spouses don’t understand why one would devote that type of time to something that can be purchased new at the local office store when there are plenty of other useful things to do around the house. The serving tray is nice because you can just shove it somewhere.
-Lastly, place two pieces of tape at the top of the work tray: one flat about 10 cm long and the other with the ends folded back to keep the sticky side up. This is the landing pad for the rubber feet (nonsticky-side-up piece) and the screws & springs (sticky-side up).

*) Go to the link in my above post and review the photos. (EDIT: The photos in Jeff's post are also encreadibly helpful in seeing the guts before you dive in.)
1) Remove the batteries.
2) Remove the rubber feet by using the X-acto knife or needle.
3) Remove the six screws and put them on the sticky-side-up tape.
4) Remove the back cover and put the two springs next to the screws. I put another piece of tape over the batch to keep them all together. (Photo 1 & 2)
5) Gently lift the LCD/cushion foam set away from the front cover. You can use the plastic pry piece, but I urge you to go at it very, very slowly. Some folks have had success changing the temperature to alter the adhesive properties of the double-sided goo. Mine worked just time with slow and gentle pressure. Flip this package over and cover with a lint-free cloth. (Photo 3)
6) With gentle pressure again, press out the screen cover from the front while lifting from the back. Remove any residue on the inside front of the calculator.
7) Now look at the old cover. There is cushion foam that frames the original cover. BE VERY CAREFUL WHEN REMOVING THIS; you want to use it again. The adhesive is very tenacious and the foam is weak and stretchy. Maybe lifting it away with while working the gap with the edge of the X-acto blade may work as well. To be honest, I just started pulling gently and did end up with a bit of stretching and tearing. As I put it back together, I just mushed it back into place best as possible and it worked out right in the end. Set this very lightly aside somewhere.
8) Prepare your new screen by covering the new front part with tape. (Remember… the type that comes off easily and doesn’t leave sticky leftovers.)
9) Match up the old screen and mark up the corners on the new plastic. Now for cutting fun! I used a ruler and placed it to the outside of new cover and on the markings. Then ever so carefully, I scored the new edge before cutting through with a few strokes. About five to six did the trick.
*This may take a couple of runs if you goof up somewhere.
10) Test fit the new screen cover.
11) Put the foam boarder back on the inside of the new piece. (Photo 4)
12) Remove the tape from the front and put this front-side up on a piece of cloth.
13) Replace the double-sided adhesive that will hold the new cover in place to the front of the calculator. Place strips of new double-sided tape to the front along the edge at a width slightly less than the inside ledges of the hole in the calculators front plate. (Photo 5) Then trim off the excess.
14) Place the new cover into the front plate and carefully seat it. (Photo 6)
15) Replace the LCD/foam cushion over the cover and check the alignment. Obviously, you will need to put the springs back in, close the back, and replace the batteries. (Photo 7. You can see, I eagerly put the screws back in, too. This was when I decided to fix the screen alignment issue that bugged me from about thirty seconds after I turned the calculator on for the first time.)
16) If needed, cut a little shim – I used a piece of a plastic zip-tie; the thickness was perfect. Yours may not need adjustment. If less adjustment is needed, use a thinner shim or grind the thicker one down (pop a piece of double-sided tape between your finger and the shim this work it over a nail file?). Stuff this shim between the screw post and the LCD frame. Check the alignment. If it is good, pry enough of a gap to wick a small bead of the superglue into the space between the screw post and the shim. (If you have decent humidity, this should cure in around ten seconds.) (Photo 8)
17) Confirm alignment. (Photo 9)
18) Put your new rig back together and show off to yourself. (Photos 10, 11, and 12)

(Photo 13 was only to show off my spiral bound manual. Na-na-na-na-nah-nah!)

Best of luck!

EDIT: Fixed line spacing and spelling

Edited: 23 Aug 2010, 2:36 p.m.

[ Return to Index | Top of Index ]

Go back to the main exhibit hall