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HP Forum Archive 08

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HP11C repair
Message #1 Posted by Charles Galloway on 11 May 2002, 9:45 p.m.

My 11c has started to misbehave after a mere 18 years. The problem appears to be with the keyboard which either does not respond, switches into PRGM mode or just changes the number typed in into something completely different.

The self test (x/on) is ok and initially so was the keyboard test but recently it has started to show "error 9" on the "1/x" or "CHS" keys. I have taken out the batteries for a day and shorted across the terminals but not seen any improvement.

I suppose that the next step is to open it up but I don't know what to look for next. Does anyone have any experience or solutions to this type of problem ?

Regards Charles Galloway

      
Re: HP11C repair
Message #2 Posted by Vieira, Luiz C. (Brazil) on 13 May 2002, 9:50 a.m.,
in response to message #1 by Charles Galloway

Hello;

The voyagers (10-series, say, 10C, 11C, 12C, 16C and 16C) have two different internals: the first series had a separate flex-PCB with all IC's plus LCD, and a separate keyboard. The second production offered a single all-built-in PCB, with IC's, LCD and keyboard. I have a non-operating (for now; I'll find the time to go for it) HP15C and another full-operative unit, both different. It is easier to repair the earlier models, but as it seems you have some problem with the keyboard, it would be hard in both cases.

You can open the unit by unscrewing four screws under the four rubber feet. PLEASE, take care with two small springs inside the calculator. They keep contact between both aluminum plates (decorative and keyboard labels) and the bottom plate (general information). They are for ESD protection and must be safely stored (one beside batteries compartment and the other at the lower right, between third and fourth rows).

If there is only one big PCB from top to bottom, yours is a new model; if there is a separate assy under (built under) the LCD, yours is an earlier model. In the second case, you can remove the IC's/LCD assy and check if there is any sort of dust between the assy and the keyboard's PCB. (PLEASE, also take care with 8 (eight) small shock-absorber foams; the LCD assy is built on four posts, and there are 2 foams for each, top and bottom. Keep them in a safe place.) There is a small conductive foam between the assy and the keyboard.

If yours is a new type, you should check if there is anything wrong with the rightmost IC: this one reads the keyboard, and I have once replaced a 16C's for an 11C's (they were the same in those units). If you believe you'll have to look at the other side of the PCB to check for problems, then there is a big job ahead: removing it. All plastic posts are used to retain the PCB, so they all must be carefully worked. After that, removing the PCB is easy (lookout for the keys...).

Well, cleaning the unit's guts is the next step. Let us know if you are getting success for now.

Cheers.

(PLEASE, FALKS! Allow me to write in a better way. If there is something written in here that is wrong or could be better expressed, let me know. I usually learn fast... Thanks.)

            
Re: HP11C repair
Message #3 Posted by doug on 13 May 2002, 12:46 p.m.,
in response to message #2 by Vieira, Luiz C. (Brazil)

One the PCB is removed on a single PCB unit, how would you put it back on since the plastic post caps are gone?

                  
Re: HP11C repair
Message #4 Posted by Vieira, Luiz C. (Brazil) on 13 May 2002, 3:19 p.m.,
in response to message #3 by doug

Hi;

I have experienced that the posts may have their upper part carefully removed without removing the post completely, say, they act as thermal rivets and only their upper parts need to be removed. When carefully worked, you can place the PCB back to the calculator's box and rework some of them (about half of them) with epoxy glue. This way, it's gonna be easy to open the unit again, if needed.

The last time I did that was in 1990, and I remember I had a mix of different glues I found to be the best, non-destructive ones for the job. Maybe we can find something better for these days... I thought about silicon-based glue.

Hope this clarifies. Cheers.

                        
Re: HP11C repair
Message #5 Posted by doug on 13 May 2002, 9:03 p.m.,
in response to message #4 by Vieira, Luiz C. (Brazil)

I have thougt about glues. And I went on the websites and searched. I am now trying to find a college that has a glue Degree so I can only spend four years learning so I can make the right choice. (;O)

                              
Re: HP11C repair
Message #6 Posted by Spice_Man on 13 May 2002, 10:33 p.m.,
in response to message #5 by doug

Actually, you can get a degree in chemical and mechanical engineering with an emphasis on adhesives... in fact many have done Ph.D. theses on glues.

On a more serious note, the heat stakes can be quickly bonded using UV cure epoxy. Of course, you'll need a UV light source of proper wavelength for the particular epoxy...

                                    
Re: HP11C repair
Message #7 Posted by doug on 13 May 2002, 11:06 p.m.,
in response to message #6 by Spice_Man

OK, I have to ask. Why an epoxy that is activated by UV rays?

Does it finish more like a glue or like a latex rubber?

The reason I brought all of this up is this. Since the post tops are gone, what is anything going to bond to except the very tiny top of the plastic stakes to the PCB itself? In other words the substance has to fill up the place around the stake and PCB and be thick enough and strong enough to make a pseudo stake top to hold the pressure of the keystrokes. Especially from heavy key bangers, and they do exist.

People could actually try to melt plastic and drip it onto the stakes but that is risky, and wouldn't be very nice odor to endure. Also if you have a hot iron for just a second and drip to hot of plastic or simply touch it on the stake to flatten it out and the whole stake could easily and quickly disappear.

                                          
Re: HP11C repair
Message #8 Posted by Spice_Man on 14 May 2002, 2:09 a.m.,
in response to message #7 by doug

> Why an epoxy that is activated by UV rays?

Because it will bond in seconds exposed to intense UV rays, rather than air-dry epoxy which will take hours to harden.

This prevents you having to use some sort of clamp contraption to keep the board in place while it hardens. If you don't put pressure on the board into the stakes while it hardens, the keys won't feel right.

The epoxy actually does a pretty good job of bonding together the tops (and slight bit of the side of) of the heat stakes to the board.

                                                
Re: HP11C repair
Message #9 Posted by doug on 14 May 2002, 1:27 p.m.,
in response to message #8 by Spice_Man

Resonable reasons Good answers. Great explanation. Thank you.

Do you have a brand name, actual product name, vendor name, url, price, for the epoxy and the UV light also?

                                          
Re: HP11C repair
Message #10 Posted by warren on 14 May 2002, 7:15 a.m.,
in response to message #7 by doug

Just empahsizing a point made in passing by Spice_Man: when trimming off the heat stakes, remove only the part that is "mushroomed" over. Do not remove the shaft of the heat stake that protrudes above the level of the circuit board. That will leave a much better place for any glue or other adhesive to grip.

                                                
Re: HP11C repair
Message #11 Posted by Vieira, Luiz C. (Brazil) on 14 May 2002, 9:25 a.m.,
in response to message #10 by warren

Hi;

I can explain that in Portuguese; now I know how to do it in English (this is the English that is not taught at the Language Schools).

When you say "Do not remove the shaft of the heat stake that protrudes above the level of the circuit board" you mean exactly what I could not express in a better way than "All plastic posts (...) must be carefully worked".

Thanks and best regards.

                                                
Re: HP11C repair
Message #12 Posted by doug on 14 May 2002, 1:30 p.m.,
in response to message #10 by warren

I have discussed this with others. I use to try to crimp the mushroom sections with needle nose pliers. That does not do very well. I then used the standard sharp cutters, like for solder. They cut smooth and even but pretty flush to the PCB. What method do you do to just get the fanned out area of the plastic?

                                                      
Re: HP11C repair
Message #13 Posted by Vieira, Luiz C. (Brazil) on 14 May 2002, 3:18 p.m.,
in response to message #12 by doug

Hello;

Hope I can find the right words (in English) to explain.

I once (upon a time) found an old mini-stereo pin that I disassembled. The common contact (outer) is a hollow metal pipe and, by carefully using a drewler, I could sharpen the edges of one of its extreme holes. This way, I could build a cutter that could cut in hole format. It was easy to cut only the excessive plastic of the stakes and leave the protuberous (got that!) part intact.

If it is not so easy to understand, I can add some drawings (I'll have to build another one, cause I lost my old tool).

Best regards.

(I'm using a terminal with no interrogation symbol available at the keyboard...)

                                                            
Re: HP11C repair - Just an add-in
Message #14 Posted by Vieira, Luiz C. (Brazil) on 14 May 2002, 3:32 p.m.,
in response to message #13 by Vieira, Luiz C. (Brazil)

I did not take the time to revise what I wrote, so please, remove

"excessive plastic of the stakes and leave the protuberous part intact"

and place:

"mushroomed part of the heat stake and leave the protruding shaft".

Thanks.

                                                      
Re: HP11C repair
Message #15 Posted by David Smith on 14 May 2002, 4:55 p.m.,
in response to message #12 by doug

You can get thin wall brass tubing of just about any size at most hobby shops. You can sharpen the edge of one end with sand paper and use it as a circular knife to cut off the edges of the heat stakes.

                                                      
Re: HP11C repair
Message #16 Posted by Ellis Easley on 14 May 2002, 4:57 p.m.,
in response to message #12 by doug

I have disassembled a 12C and a 15C and reassembled the 15C. I cut the spread plastic with an Exacto knife between the plastic and the PCB. Sometimes I cut off the top but sometimes only the outer ring of plastic popped off.

When I reassembled the 15C, I used some regular cyanoacrylate superglue that had thickened over time. I understand you can buy superglue that is made thick to fill gaps. My concern about regular thin superglue would be that it might run all over the contacts. I glued one post at a time and held the assembly tightly with my fingers until the glue set (I had a few hours to waste!) Before I reassemble the 12C, I'm going to build a fixture with a number of metal rods to provide pressure, so I can glue everything at once and have more choice of glues. (I think epoxy would be good.) In the meantime (since approximately election day 1988, when I found the 12C in the street where it had been run over) I have a pad inside the 12C made by stacking pieces of duct tape ("the handyman's secret weapon"!) which does a pretty good job of pressing the keyboard againt the bezel. Of course, the feel of the keys is somewhat spongy.

I would like to find some tiny screws with relatively broad heads to thread into tiny holes drilled into the tops of the posts (with a drill press, to make sure I don't drill through!).

                                                            
Re: HP11C repair
Message #17 Posted by Erik Wahlin on 14 May 2002, 6:48 p.m.,
in response to message #16 by Ellis Easley

I have used a sharp tipped solder iron to do the repair. You can re-mushroom the heatstake post to some degree.

                                                            
Re: HP11C repair
Message #18 Posted by Vieira, Luiz C. (Brazil) on 15 May 2002, 6:42 a.m.,
in response to message #16 by Ellis Easley

Hi;

I have also tried to find these tiny screws that I have seen in many minicalcs made in somewherelse. Those subminicalcs have subminiscrews that would do the job. Does anybody know where to find them? I have some (less than 8) that would be of no help at all, but I once tried using them. After opening a tiny hole (irregularly drew), I got success screwing in, but after removing it, the remaning thread was too weak that it could not retain the tiny screw back there.

Cheers.

                                                                  
Re: HP11C repair
Message #19 Posted by Ellis Easley on 17 May 2002, 1:52 a.m.,
in response to message #18 by Vieira, Luiz C. (Brazil)

I learned (working at a Tandy computer factory) that there are some tricks to using screws in plastic: first, there are special types of screw threads for the purpose, one trademark is Plastite. These screws look like a sheet-metal screw except they usually have a rather blunt tip (not pointed, anyway), if you look at the thread end-on, you see that there is a triangular profile to the outer extremes of the thread. Also, a very critical thing is the size of the hole which must be just right for the particular thread size. I wonder if the small parts warehouse website might have this kind of thing (you would think so!)

                                                                        
Re: HP11C repair - Extended
Message #20 Posted by Vieira, Luiz C. (Brazil) on 17 May 2002, 7:58 a.m.,
in response to message #19 by Ellis Easley

Hi;

thanks for the tips, Ellis. As you may have noticed, here, in some regions of my country, we do not have an easier access to some sort of good stuff. Take this: I lost (or do not remember where did I put) those big screws that hold the upper side of the 41īs box, top and botton parts, lined with the BATT/IO assy, you know? I was told, after looking for them almost everywhere closed to the citty I live, that those were kind of special screws, and that it would not be easy to find something like them. After some days of searching, I found nothing but the small screws. Well, there is a little HP41C waiting for those to be revived.

About the HP11C (and all voyagers), I know the screw youīre talking about. It seems that the little tip acts like a cutter, creating a path prior to the thread itself. For sure this is the actual screw for the job. Iīll try to find something like them. Well, after finding those screws, there is also a question: will the posts (stakes) be strong enough to hold the screws? As you mentioned, there are some tricks using screws on plastic, and the thickness of the remaining material, the stakes, is also critical, isnīt it?

Thanks.

Best regards

                                                                              
Re: HP11C repair - Extended
Message #21 Posted by Ellis Easley on 17 May 2002, 4:04 p.m.,
in response to message #20 by Vieira, Luiz C. (Brazil)

Luiz, you wrote: Well, after finding those screws, there is also a question: will the posts (stakes) be strong enough to hold the screws? As you mentioned, there are some tricks using screws on plastic, and the thickness of the remaining material, the stakes, is also critical, isnīt it?

That's why the size of the hole is so critical. Also with very tiny screws, I think the torque would have to be limited very carefully (a cautious hand should be enough). The screws are self tapping but while sheet metal screws can go into a tiny hole (with their sharp point) and then count on the sheet metal to deflect outward away from the screw as the diameter increases, a screw threading into a plastic post will split it if the hole is too small, and will fail to cut a reliably deep thread if the hole is too large. Each screw size has a recommended hole diameter which might depend somewhat on the material and the ultimate wall thickness. As I recall, the posts on the Voyager are about 0.05 inch in diameter. Without knowing the actual limits, I would guess that the hole should be no larger that 1/3 of the diameter or about 16/1000 inch - less than 1/2 mm. I just looked at smallparts.com, they don't list any screws specially made for plastic. The smallest sheet metal screws they have are #000 which is .0341 inch diameter and cost $26 for 10! They are flat headed and would require the corresponding #000 flat washer - .040 ID, .090 OD, 10 for $6.50 but this size is too big anyway. In machine screws, there is a set of sizes called "Unified National Miniature" (UNM, not to be confused with the University of New Mexico, my parents' alma mater!) which goes down to 0.5 mm diameter, .06 and .12 inches long - that's how they are described in the catalog, two different units - they cost $6.85 each!! (10 for $47.50). I don't find any washers to go with these screws and the catalog doesn't say how big the heads are - it just says they are "slotted, fillister" head.

                                                                                    
Re: HP11C repair - ACK
Message #22 Posted by Vieira, Luiz C. (Brazil) on 18 May 2002, 9:25 a.m.,
in response to message #21 by Ellis Easley

Hi;

thanks, Ellis; your explanations clarify A LOT, mam! As you mentioned, you were indeed in the business.

After that, I believe heat or epoxy glue will be the best choice to hold the voyagers' keyboards. Anyway, I have now some more knowledge about plastics, screws and the like.

Thanks again and best regards.

                                                      
Re: HP11C repair
Message #23 Posted by warren on 15 May 2002, 7:31 a.m.,
in response to message #12 by doug

The one time I performed this dis-assembly, I used an exacto knife as Ellis Easley suggested. Just hold the blade perpendicular to the keyboard, and slice down through the mushroomed portion. It of course takes several slices around the circumference of the shaft, and you don't necessarily end up with a perfect circle, but it is fairly simple (although quite time consuming) to do.
Regarding re-assembly, I must admit that I have not tried this yet. Something that would be easy to apply, set quickly, hold tightly, yet be removable if needed for future repairs is all that is needed. One technique I heard was to use hot glue from a glue gun. Just push down on the board next to a stake or two, put a drop of glue on, and hold until it cools. Like I said, I haven’t put mine back together, so I don't know how well this would work or how easy it would be to do. There has been discussion in this Forum in the past of some sort of glue used to repair or otherwise glue the tires on radio controlled cars. My recollection is that it is sort of a semi-solid black glue. This might hold well and be easier to apply than hot glue, but then the clamping and holding issue remains. A jig to hold everything together sounds like a good idea. Let us know if you try any of these things and if you have any success, good luck.

                                                            
Re: HP11C repair
Message #24 Posted by David Smith on 15 May 2002, 2:06 p.m.,
in response to message #23 by warren

The glue is IC-2000 tire cement. It is a cyanoacrylate super glue that has been rubberized by the addition of some black goo. Works very well and does not set up brittle like most CA glues. One thing you should be aware of with any CA is that it will outgass for quite a while after apparently setting up. If you close up your machine before it has totally cured then it can deposit a thin (non-conductive) scuzz inside the machine. This can cause problems with key contacts.


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