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My crazy HP 15c repair
05-07-2020, 04:58 PM
Post: #1
My crazy HP 15c repair
Hi guys
I am working on an interesting thing. I got from an old friend a HP 15c. It is working, BUT it has been abused badly:

* dropped on the floor several times. A little piece from the rear half of the plastic case is broken off. Besides that, almost ALL of the internal heat stakes are broken, and one of the pieces was now between the LCD module and the front window.
* it was used in a smoker household: the entire keypad and front panel is full of ... don't know how I should call it, sticky goo. Even the keys were almost unreadable.
* doesn't pass the keyboard self test: because the keyboard is held by those internal heat stakes, the keys don't make good contact all the time. So sometimes it is not possible to push them all.

Since I actually want to use this calculator, I have decided to open it and tried to clean it. It works! looks almost like brand new! and after I cleaned the LCD module, it looks nice and sharp and crisp. It even passes the self test ;-)

Now two questions:

1. I have found two very tiny springs on my desk. They MUST be from this calculator, because I don't know from what else they should be ;-) so where do they belong?
2. How to reassemble it: I have put in the keys and this little rubber mat which is under the keys. All good so far and I can also but the PCB back in. Since the heat stakes are broken off, it will not be possible to melt all of them with my soldering iron. On the other hand it is necessary to have a very good pressure from the PCB to the front panel. So I thought about a different method: if I would put a piece of foam rubber or neoprene between the PCB and the calculator back case, that would give some pressure and press the PCB nice and tightly to the front panel. Any better ideas? I am not a particular friend of gluing. And I also don't really like those heat stakes.


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05-07-2020, 06:38 PM
Post: #2
RE: My crazy HP 15c repair
There have been several posts in the past (Google "HP 15c spring") about the springs which, when the calculator is lying down, extend vertically between the front and back metal plates. They provide an electrical connection between them so that any electrostatic discharge when using it can travel from front to back and out, bypassing the electronics. Look for two small holes in the plastic front and back that let you see the inside side of the metal plate. Those are where the springs should go.

Best to you and your '15!

So many signals, so little bandwidth!
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05-07-2020, 06:43 PM
Post: #3
RE: My crazy HP 15c repair
From a post by Randy (20041130):

Quote:top left and bottom right sides, they are inside a small molded tube. The longer one lives next to the battery holder.

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05-08-2020, 08:21 AM
Post: #4
RE: My crazy HP 15c repair
Hi guys
good, I found where the springs belong and put them back. Also for the heat stakes, I tried another idea:
I kept those little "mushroom" heads that broke off from the top of those heat stakes. After I had reinstalled the PCB, I melted those little plastic bits and put them back where they were before. See the attached picture where I have reinstalled a couple of them. After I had most of the heat stakes back in place, I tested the keys, and ALL OF THEM work fine now!
Put the calculator back together and now everything is fixed: the keys are not loose, they don't rattle, the display is clear and crisp again and the calculator looks almost like new!

The only remaining problem now is the missing hp Logo. Any ideas where I could get a HP 15c Logo for my machine? I am thinking about milling my own. I have a little CNC mill and could perhaps make one of these hp logos from aluminium. However if someone has a better idea or could even sell me a "used" logo from a broken machine that would perhaps be better.

Also for the heat stakes; I am pretty happy how tight the keyboard is now, but I am afraid that it won't last forever. Anyone has a better idea how it could be put together in a more professional way? :-)


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05-08-2020, 11:22 AM (This post was last modified: 05-08-2020 11:23 AM by BillBee.)
Post: #5
RE: My crazy HP 15c repair
Congrats!! I have an 11c that needs that procedure for a display swap but those heat stakes are all intact. Once in awhile I will pop the back off shake my head and screw it back together. I operated on a broken 12c and it was a learning experience. Smile

Foam will probably not give the support you need and the holding capacity of the 4 case screws is questionable. The idea of a small drop of glue is not that bad an idea. The more experienced guys can probably recommend a type (gel, epoxy, etc..).

The shorter spring will be on the right hand side middle (looking at the calc upside down).

There is a great feeling when the batteries are popped in and a full display occurs.

-Bill
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05-08-2020, 01:45 PM
Post: #6
RE: My crazy HP 15c repair
(05-08-2020 08:21 AM)hb9fsx Wrote:  The only remaining problem now is the missing hp Logo. Any ideas where I could get a HP 15c Logo for my machine? I am thinking about milling my own. I have a little CNC mill and could perhaps make one of these hp logos from aluminium. However if someone has a better idea or could even sell me a "used" logo from a broken machine that would perhaps be better.

Take a look at this thread:
https://www.hpmuseum.org/forum/thread-13014.html
I bought one from him and it looks great.
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05-08-2020, 04:09 PM
Post: #7
RE: My crazy HP 15c repair
(05-08-2020 08:21 AM)hb9fsx Wrote:  ... Anyone has a better idea how it could be put together in a more professional way? :-)

A couple of threads on hot glue and super glue that might help.

Nice job!
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11-11-2023, 10:21 PM (This post was last modified: 11-11-2023 10:34 PM by wmundstock.)
Post: #8
RE: My crazy HP 15c repair
(05-07-2020 04:58 PM)hb9fsx Wrote:  Hi guys
I am working on an interesting thing. I got from an old friend a HP 15c. It is working, BUT it has been abused badly:

* dropped on the floor several times. A little piece from the rear half of the plastic case is broken off. Besides that, almost ALL of the internal heat stakes are broken, and one of the pieces was now between the LCD module and the front window.
* it was used in a smoker household: the entire keypad and front panel is full of ... don't know how I should call it, sticky goo. Even the keys were almost unreadable.
* doesn't pass the keyboard self test: because the keyboard is held by those internal heat stakes, the keys don't make good contact all the time. So sometimes it is not possible to push them all.

Since I actually want to use this calculator, I have decided to open it and tried to clean it. It works! looks almost like brand new! and after I cleaned the LCD module, it looks nice and sharp and crisp. It even passes the self test ;-)

Now two questions:

1. I have found two very tiny springs on my desk. They MUST be from this calculator, because I don't know from what else they should be ;-) so where do they belong?
2. How to reassemble it: I have put in the keys and this little rubber mat which is under the keys. All good so far and I can also but the PCB back in. Since the heat stakes are broken off, it will not be possible to melt all of them with my soldering iron. On the other hand it is necessary to have a very good pressure from the PCB to the front panel. So I thought about a different method: if I would put a piece of foam rubber or neoprene between the PCB and the calculator back case, that would give some pressure and press the PCB nice and tightly to the front panel. Any better ideas? I am not a particular friend of gluing. And I also don't really like those heat stakes.

I am planning a similar project. The 15C I got has the board saying MADE IN USA, which is good and the calculator itself says Brazil on the back.

The keys and self test are good. Enter key is working but lost its "click" feel a little bit.

My main complaint is the display. I can't tell if its dirt or what, but it is a bit opaque. It seems like the problem is the interior of the window. Maybe its made of a sandwitch with 2 films and one is peeling of. That kind of feel. Attached some pictures from the microscope.

   
   
   


Questions are:
1. I suppose to remove you have to cut the little black "smashed plastic dots". How do you recommend doing that?
2. How do you assemble it back? Do you put it back in place and melt plastic? Any thoughts on the process?
3. Can I replace that window with maybe the window of another calculator? Those with big display or something like that? What material is used there?

Thanks!
Walter
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11-12-2023, 04:15 AM
Post: #9
RE: My crazy HP 15c repair
(11-11-2023 10:21 PM)wmundstock Wrote:  
(05-07-2020 04:58 PM)hb9fsx Wrote:  Hi guys
I am working on an interesting thing. I got from an old friend a HP 15c. It is working, BUT it has been abused badly:

* dropped on the floor several times. A little piece from the rear half of the plastic case is broken off. Besides that, almost ALL of the internal heat stakes are broken, and one of the pieces was now between the LCD module and the front window.
* it was used in a smoker household: the entire keypad and front panel is full of ... don't know how I should call it, sticky goo. Even the keys were almost unreadable.
* doesn't pass the keyboard self test: because the keyboard is held by those internal heat stakes, the keys don't make good contact all the time. So sometimes it is not possible to push them all.

Since I actually want to use this calculator, I have decided to open it and tried to clean it. It works! looks almost like brand new! and after I cleaned the LCD module, it looks nice and sharp and crisp. It even passes the self test ;-)

Now two questions:

1. I have found two very tiny springs on my desk. They MUST be from this calculator, because I don't know from what else they should be ;-) so where do they belong?
2. How to reassemble it: I have put in the keys and this little rubber mat which is under the keys. All good so far and I can also but the PCB back in. Since the heat stakes are broken off, it will not be possible to melt all of them with my soldering iron. On the other hand it is necessary to have a very good pressure from the PCB to the front panel. So I thought about a different method: if I would put a piece of foam rubber or neoprene between the PCB and the calculator back case, that would give some pressure and press the PCB nice and tightly to the front panel. Any better ideas? I am not a particular friend of gluing. And I also don't really like those heat stakes.

I am planning a similar project. The 15C I got has the board saying MADE IN USA, which is good and the calculator itself says Brazil on the back.

The keys and self test are good. Enter key is working but lost its "click" feel a little bit.

My main complaint is the display. I can't tell if its dirt or what, but it is a bit opaque. It seems like the problem is the interior of the window. Maybe its made of a sandwitch with 2 films and one is peeling of. That kind of feel. Attached some pictures from the microscope.






Questions are:
1. I suppose to remove you have to cut the little black "smashed plastic dots". How do you recommend doing that?
2. How do you assemble it back? Do you put it back in place and melt plastic? Any thoughts on the process?
3. Can I replace that window with maybe the window of another calculator? Those with big display or something like that? What material is used there?

Thanks!
Walter

Maybe the old devices have screens with some sort of factory-applied protection film?

I don't see how it could be possible on a one-piece screen assembly.

HP-12C Gold / HP-12C Platinum
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11-12-2023, 02:25 PM
Post: #10
RE: My crazy HP 15c repair
(11-12-2023 04:15 AM)lvt Wrote:  Maybe the old devices have screens with some sort of factory-applied protection film?

I don't see how it could be possible on a one-piece screen assembly.

Thanks for the reply. I don't think the display is a one-piece, on this picture from the original post shows a plastic film which seems to be attached to the front frame. I think that is some sort of polarizer film, or anti reflex, something like that. You see it have a grey-ish color to it.
[Image: attachment.php?aid=8411]

And the removal of the board which I am referring to is also seen on the original post.
[Image: attachment.php?aid=8413]

Seems like hb9fx user really cut it off then melted them back into place or something like that.

Thanks.
Walter
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11-13-2023, 12:59 AM
Post: #11
RE: My crazy HP 15c repair
I don't think that you need glue for the PCB.

Just buy a small piece of rubber pad with the correct thickness then split it to several smaller pieces that can be used between the PCB and the back plate.

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11-18-2023, 01:05 PM
Post: #12
RE: My crazy HP 15c repair
(11-12-2023 04:15 AM)lvt Wrote:  Maybe the old devices have screens with some sort of factory-applied protection film?
Yes, they do. There's an anti-glare film applied to the screen surface. You need to be very careful working around that because if you pull it up accidentally there's no way to stick it back down. And completely detaching screens from Voyager shells for transplants or safer bezel refinishing is quite difficult.

There's a reference document floating around these forums somewhere from years ago that goes into a lot of detail on all these questions.
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11-22-2023, 06:38 PM (This post was last modified: 11-22-2023 06:42 PM by johnb.)
Post: #13
RE: My crazy HP 15c repair
(05-08-2020 01:45 PM)twoweims Wrote:  
(05-08-2020 08:21 AM)hb9fsx Wrote:  The only remaining problem now is the missing hp Logo. Any ideas where I could get a HP 15c Logo for my machine? I am thinking about milling my own. I have a little CNC mill and could perhaps make one of these hp logos from aluminium. However if someone has a better idea or could even sell me a "used" logo from a broken machine that would perhaps be better.

Take a look at this thread:
https://www.hpmuseum.org/forum/thread-13014.html
I bought one from him and it looks great.

Peter seems to no longer be active on MoHPC, but maybe someone else has taken up the baton?
I see you have a CNC mill. Maybe you should be that person?

Back in 2015 someone else was doing this, and I got a replacement logo for my 11c.
It's still holding up perfectly, with no wear whatsoever. So [IMHO] that's better than an original logo.

If so, if they become available in aluminum, I will definitely purchase at least:
* 2 15c logos
* 1 16c logo

I'm going to guess that these might cost $25 apiece (USD) nowadays.

Daily drivers: 15c, 32sII, 35s, 41cx, 48g, WP 34s/31s. Favorite: 16c.
Latest: 15ce, 48s, 50g. Gateway drug: 28s found in yard sale ~2009.
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11-22-2023, 07:31 PM
Post: #14
RE: My crazy HP 15c repair
(11-22-2023 06:38 PM)johnb Wrote:  
(05-08-2020 01:45 PM)twoweims Wrote:  Take a look at this thread:
https://www.hpmuseum.org/forum/thread-13014.html
I bought one from him and it looks great.

Peter seems to no longer be active on MoHPC, but maybe someone else has taken up the baton?
I see you have a CNC mill. Maybe you should be that person?

Back in 2015 someone else was doing this, and I got a replacement logo for my 11c.
It's still holding up perfectly, with no wear whatsoever. So [IMHO] that's better than an original logo.

If so, if they become available in aluminum, I will definitely purchase at least:
* 2 15c logos
* 1 16c logo

I'm going to guess that these might cost $25 apiece (USD) nowadays.

Hugh Petarni has been attempting to make replacement voyager logos and appears to be making progress. Here is a post from him on the Facebook Real Engineers Use HP Calculators public forum.
https://www.facebook.com/groups/hpcalc/p...672464690/
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11-23-2023, 12:16 AM
Post: #15
RE: My crazy HP 15c repair
Just a comment on heat stakes... I haven't tackled any voyager ones yet, but I have taken on the heat stakes in the 41c series with pretty good success. I would bet the approach to both would be pretty similar. I find that when you want to separate keyboards that are heat staked to the front of the calculator that you should to leave as much of the heat stake intact as possible. To do that I find that lifting the head of the heat stake gently all round is better than just slicing off the top, so it comes of more donut shaped. This leaves more heat stake to work with when reassembling. I mostly do not use the donuts for reassembly, but use a small blob of hot glue instead. If you want to try and reattach the donuts, it worth noting that HP tends to use ABS plastic for it's calculators, so you can easily use a liquid cement to "weld" the donuts back on to the heat stakes. That's probably going to be better than applying heat to reattach them. The other advantage of using hot glue is that you can gently heat it if you ever need to take the keyboard apart again.

HTH

Cheers,
John
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11-23-2023, 08:41 AM
Post: #16
RE: My crazy HP 15c repair
(11-23-2023 12:16 AM)Johnboy Wrote:  The other advantage of using hot glue is that you can gently heat it if you ever need to take the keyboard apart again.

You can also use IPA to remove hot glue. It doesn't really dissolve it (much), but it unsticks it from smooth surfaces very effectively.

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11-23-2023, 11:09 AM
Post: #17
RE: My crazy HP 15c repair
(11-23-2023 08:41 AM)ijabbott Wrote:  You can also use IPA to remove hot glue. It doesn't really dissolve it (much), but it unsticks it from smooth surfaces very effectively.
Well I never knew that - thanks for sharing !!
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11-23-2023, 08:33 PM (This post was last modified: 11-23-2023 08:34 PM by johnb.)
Post: #18
RE: My crazy HP 15c repair
By the way, @hb9fsx, I wanted to thank you for your bravery in tackling this project.

So far your results look beautiful!

I am a big believer that we, as a community, should be doing everything we can to prevent these machines from going to the dump heap. There were only a finite number of each model made, and even though some of them are still plentiful, their numbers will only continue to decrease, not increase.

Let's learn from other people's hard lessons... back in the 1920's, nearly EVERY movie theatre in the United States had a theatre organ of some sort --- most of them very limited and unimpressive instruments, but a lot of big, impressive ones as well. There were thousands! It wasn't until old theatres started getting torn down in the 1960's and 70's -- with their instruments still in them! -- that volunteers sat up and took notice and started trying to save these remarkable machines.

Now there are only a few hundred theatre organs left.

Save the HP's! Save the HP's!

Daily drivers: 15c, 32sII, 35s, 41cx, 48g, WP 34s/31s. Favorite: 16c.
Latest: 15ce, 48s, 50g. Gateway drug: 28s found in yard sale ~2009.
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