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isanchez · (This post was last modified: 05-01-2020 04:48 PM by isanchez.)

Hi,
I hate opening classic models because it is almost impossible to release the back sticker without causing a damage. Sometimes this damage is very small, but it is always there. Moreover, if this sticker and the calculator are in perfect state...this is the case of my HP35 (4th version). I would like to share with you my experience. Maybe can be of help.

I have to say that this HP35 looks absolutely new. I have a nice collection of HP35's, but none like this. Some weeks ago I realised that the display was failing. The middle bank of five led bubbles, did not displayed the upper segment, in all five digits of the mentioned bank... I wondered how to open it without ruining the sticker.

My solution was to drill two small holes inside the battery compartment, in order to cut the two screws under the sticker. I discovered that it is not necessary to measure the position of these two screws...there are two small marks in the plastic surface that show their position. The holes should be placed in the bottom half of the calculator, right over the mentioned "marks" in the plastic (this is important). I started first with a very thin drill (1.5mm), using a manual driller (see pictures). When I reached the metal screws, I changed to a Dremel with a thicker drill (3mm-3.5mm). As result, both screws got cut and the calculator was disassembled without affecting the sticker.

On the other hand, you get two small holes in the battery compartiment, but they are not visible at all and, if you want, they can be filled with black putty or black silicone.

As I said, I share some pictures of the process (and the dsiplay failure), available here: https://we.tl/t-HLQF1mHtCf

Following with the repair process, now I would request of your help: Where do you think it lies the problem: is it the display driver, a contact or more surely the full bank of leds? As I see that exactly all upper segments of the whole middle bank are missing, I got doubts of what is more probable, to start with ;-D.
Can I use the HP45 leds?

Well this is it, Thanks and kind regards!!

Ignacio

toml_12953 · 05-01-2020, 03:11 PM

(05-01-2020 01:30 PM)isanchez Wrote: On the other hand, you get two small holes in the battery compartiment, but they are not visible at all and, if you want, they can be filled with black putty or black silicone.

As I said, I share some pictures of the process (and the dsiplay failure), available here: https://we.tl/t-HLQF1mHtCf

Ignacio

Very nice job! How do you put it back together again, though? Do you just leave out those two screws?

isanchez · 05-01-2020, 04:47 PM

(05-01-2020 03:11 PM)toml_12953 Wrote:
(05-01-2020 01:30 PM)isanchez Wrote: On the other hand, you get two small holes in the battery compartiment, but they are not visible at all and, if you want, they can be filled with black putty or black silicone.

As I said, I share some pictures of the process (and the dsiplay failure), available here: https://we.tl/t-HLQF1mHtCf

Ignacio

Very nice job! How do you put it back together again, though? Do you just leave out those two screws?

Hi,
I never screwed these two back in place (neither with the sticker method nor in this new approach, obviously in this case, because there is no way to do it) . If it is necessary to open it again, then you have to release the sticker, again, and this means more damage. I consider these two screws are not necessary at all to keep the calculator safely closed, at least from my experience.
Regards

Ignacio

aurelio · (This post was last modified: 05-01-2020 05:32 PM by aurelio.)

Ignacio, a great job and thank-you for sharing, but forgive me, you decided to drill the calculator and to break the posts (I realize they are not visible from the outside ) of your calculator, I mean to "damage" the body of the 35 just to not cause a damage to a sticker, while opening the case??

Maybe I'm wrong, but all my life I'm going to remove the sticker, if it's for a good cause... Smile

isanchez · 05-01-2020, 05:56 PM

(05-01-2020 05:29 PM)aurelio Wrote: Ignacio, a great job and thank-you for sharing, but forgive me, you decided to drill the calculator and to break the posts (I realize they are not visible from the outside ) of your calculator, I mean to "damage" the body of the 35 just to not cause a damage to a sticker, while opening the case??

Maybe I'm wrong, but all my life I'm going to remove the sticker, if it's for a good cause...

Hi,
Nothing to forgive. Answering to your question: yes

Regards

toml_12953 · 05-01-2020, 07:00 PM

(05-01-2020 05:29 PM)aurelio Wrote: Ignacio, a great job and thank-you for sharing, but forgive me, you decided to drill the calculator and to break the posts (I realize they are not visible from the outside ) of your calculator, I mean to "damage" the body of the 35 just to not cause a damage to a sticker, while opening the case??

Maybe I'm wrong, but all my life I'm going to remove the sticker, if it's for a good cause...

I could overlook the slight damage inside the battery case but a wrinkled sticker would catch my eye every time I looked at it.

Moggul · 05-01-2020, 08:59 PM

I doubt all the upper segments in a bank would go bad at the same time so I'd think it should be either contacts or display driver, most probably the former.

aurelio · 05-01-2020, 09:01 PM

(05-01-2020 07:00 PM)toml_12953 Wrote:
(05-01-2020 05:29 PM)aurelio Wrote: Ignacio, a great job and thank-you for sharing, but forgive me, you decided to drill the calculator and to break the posts (I realize they are not visible from the outside ) of your calculator, I mean to "damage" the body of the 35 just to not cause a damage to a sticker, while opening the case??

Maybe I'm wrong, but all my life I'm going to remove the sticker, if it's for a good cause...

I could overlook the slight damage inside the battery case but a wrinkled sticker would catch my eye every time I looked at it.

I will show you a couple of my 35s, a 4th series which looks well cosmetically and it works fine (never opened), I've just retouched the silver on the bar and a 3rd series also working and unopened but with the silver a bit worn (just a dot). I did not tryed to renew it, it's too difficult 'cause the original silver is naturally yellowed by the age (maybe by the smoke of the previous owner, I'm not sure of that).
At first I was sorry, I admit, but I changed soon my mind: I'll leave it "as is", and I love it: it's old and pretty aged Smile

teenix · (This post was last modified: 05-02-2020 01:49 AM by teenix.)

(05-01-2020 01:30 PM)isanchez Wrote: Following with the repair process, now I would request of your help: Where do you think it lies the problem: is it the display driver, a contact or more surely the full bank of leds? As I see that exactly all upper segments of the whole middle bank are missing, I got doubts of what is more probable, to start with ;-D.
Can I use the HP45 leds?

Well this is it, Thanks and kind regards!!

Ignacio

If all the top LED segments were not working I would suspect the anode driver or the circuit board, however in this case it is probably the LED package or the circuit board.

The upper segment is called the "A" segment. It is powered through the top left pin (looking down at the bubble lens side).

I would first check the connection to this pin on the circuit board. Look for corrosion or broken circuit track. Try soldering the pin again. (Not too much heat or you could destroy something inside)

If that fails then...

The same LED anodes are all connected together inside the LED package. If you look closely at it through the top you will see all the small wires doing the job. I suspect the connection from the outside pin to these LEDs has failed inside the package.

Yes, HP-45 LED packages will work in the 35.

cheers

Tony

isanchez · 05-02-2020, 07:16 AM

(05-02-2020 01:39 AM)teenix Wrote:
(05-01-2020 01:30 PM)isanchez Wrote: Following with the repair process, now I would request of your help: Where do you think it lies the problem: is it the display driver, a contact or more surely the full bank of leds? As I see that exactly all upper segments of the whole middle bank are missing, I got doubts of what is more probable, to start with ;-D.
Can I use the HP45 leds?

Well this is it, Thanks and kind regards!!

Ignacio

If all the top LED segments were not working I would suspect the anode driver or the circuit board, however in this case it is probably the LED package or the circuit board.

The upper segment is called the "A" segment. It is powered through the top left pin (looking down at the bubble lens side).

I would first check the connection to this pin on the circuit board. Look for corrosion or broken circuit track. Try soldering the pin again. (Not too much heat or you could destroy something inside)

If that fails then...

The same LED anodes are all connected together inside the LED package. If you look closely at it through the top you will see all the small wires doing the job. I suspect the connection from the outside pin to these LEDs has failed inside the package.

Yes, HP-45 LED packages will work in the 35.

cheers

Tony

Thanks a lot!, Tony and Moggul
It is very clear now. I go ahead with it!

Kind regards!

Geoff Quickfall · (This post was last modified: 05-02-2020 07:51 AM by Geoff Quickfall.)

It is not impossible to release the back sticker on the classics without damaging them; or put it another way; It is possible to remove the classic labels without damaging them.

In fact I have removed the front bezel/label off the HP42S to gain access to the heat stakes in order to release the two shells from each other.

Follow this link for an HP article I wrote and apply the same technique to the classic labels.

I have used this process on over 60 classics for myself and others without any damage, creases or cracks and replaced them back in place with no evidence they have been removed.

Here is a step by step menu on releasing the classic labels:
HPSolve article

Geoff

isanchez · 05-02-2020, 08:11 AM

(05-02-2020 07:16 AM)isanchez Wrote:
(05-02-2020 01:39 AM)teenix Wrote: If all the top LED segments were not working I would suspect the anode driver or the circuit board, however in this case it is probably the LED package or the circuit board.

The upper segment is called the "A" segment. It is powered through the top left pin (looking down at the bubble lens side).

I would first check the connection to this pin on the circuit board. Look for corrosion or broken circuit track. Try soldering the pin again. (Not too much heat or you could destroy something inside)

If that fails then...

The same LED anodes are all connected together inside the LED package. If you look closely at it through the top you will see all the small wires doing the job. I suspect the connection from the outside pin to these LEDs has failed inside the package.

Yes, HP-45 LED packages will work in the 35.

cheers

Tony

Thanks a lot!, Tony and Moggul
It is very clear now. I go ahead with it!

Kind regards!

SOLVED: bad led bank ...thanks a lot Tony!!

(to finalise this "surprising" debate: maybe it was my fault not to state clearly that the explained method is not mandatory).

Kind regards