Restoration Guide, ideas, help, suggestions and etc....


Hello all!

I have been thinking of a publication project and want to know if it would be recieved by the HP community. I am looking to cover production only and shipping only.

Also, I will be floating some ideas out there and want to make sure credit is given where it is due. For example, Katie's HP 97 printer gear solution or Karls dental floss spice opening technique, Card reader o-rings or tube solutions and etc.

I know for a fact that I am not the only one that has independently, or with research, come across an idea for restoration and I want to make sure I acknowledge the originators.

There will probably be an extensive bibliography!!! I am, however, going to, or have done all the projects myself that will be included. All photos will be original by me for consistency of publication.

I have quite a collection of restoration photos made up now. Raw images and labeled all done on the blue background. I do this intentionally so that any booklet will have matching photos throughout.

So far the book will include:

1.  HP 65 ground up restoration complete with about 25 labled
figures including PCB, Card Reader, exterior finish, etc.
This will be the most in depth restoration it explains all
that can go wrong with a classic, and many subsequent models

2. HP 97 gear replacement, cleaning, case restoration and a light
focus on the specific card reader and printer removal. The
rest of the techniques would be covered on the HP 65.

3. Woodstock restoration including keys, switches,
(non invasive techniques for cleaning and restoring)

4. Spice opening and restoration as in this posting

5. Voyager opening, keyboard repair as well as keyboard
dis-assembly, yes the dreaded rivet removal and replacement

6. Pioneer repairs as well as case opening and memory enhancement
of the 42S and quartz timing crystal installation (?)

7. Stretch Pioneer repairs, case opening and etc

8. HP 01 cricket repairs and case restorations

9. HP 9825A tape deck repair and printer repair as well as the
typical case restoration and etc.

10. HP 71B opening and ribbon repair, aluminum bezel finish
restoration, keyboard resurrection....

11. TDS memory card battery change.

12. and of course every thing to do with the HP 41 and it's
card reader including battery post problems, corrosion problems
keyboards and etc. (thanks for reminding me that I forgot to
include the 41 especially this year).

Of course there will be overlap so after the HP 65 main restoration topic, the other chapters will be specific to the challenges that each series/family present to the restorer.

Many appendixes with tool lists, polish and compound used for cleaning, cleaning solutions that have been successfully tested and etc.

There will be many colour pictures, which will increase the cost but as this is an 'on demand publication' the costs will be kept lower.

What will not be included at this time is an in depth electronic
repair section, not my forte. However this may change with help from you, the community, as the project matures.

So the question is:

Is there an interest in a 50 to 100 page book full of how to illustrations, before and after photos, labelled figures, tool requirements and restoration techniques with appendices including diagnostic programs for the 65, 67 and 97?

Let me know as I will be doing this anyway, for me! (in fact the 20 page HP 65 restoration section is already completed) and the photos for 90% of the book project have all ready been taken.

Hope to hear from you all,


Edited: 30 May 2009, 4:18 a.m. after one or more responses were posted


The HP 9825 tape repair techniques probably ought to be in a separate book. (I'd want it.) In fact, each calculator series might be in its own ebook. You could probably charge $9.95 for each ebook with a discount for the entire library.


Steve, get some sleep.

The E book sounds like an interesting idea.! And the HP9825A might be more your forte, especially the tape drive. I will proceed as far as I can go and document the steps in any case.

Cheers, Geoff

P.S. your link to the HP 45 restoration has been broken. I should stick it in the articles section but will have to find it in the archives again.

Cheers again, Geoff

Edited: 30 May 2009, 4:23 a.m.


Geoff - Greetings from the NCR

I would definitely be interested in your booklet. I have successfully (i.e. no damage that I am aware of) opened up Spice units half a dozen times using the method described at But understand how it can be a risky understaking... It's funny, but I remember trying Karl's floss method a couple of years ago and was unsuccessful at that one (maybe the floss was too thin).

Anyway, I own at least one Woodstock, Spice, Voyager, HP-41, Pioneer series calculator so I could benefit from your manual. Great photos and enviable collection, by the way! I want to 'memory enhance' one of my 42's!




the method described here (as mentioned)

was shown to me by Tony Duell. He gets the credit for this method. I tried the floss method, but it didnt work for me. perhaps my floss was too thin/weak etc. not sure.

Tony's spice opening method involves applying pressure in a certain way that is difficult to describe in words, you have to really see it and try it.

one other thing. i've been told my scraping the contact method to clean them is not recommended!


Edited: 31 May 2009, 9:50 a.m.


Hello Hugh,

That was my preferred method until I found 5 of these spices in a box all exhibiting the same intermittant LED faults. It involved simutaneously pulling the bottom shell towards you while pushing the top shell away.

The method was dependent on the stiffness of the latch and whether or not the bottom shell would slide out of the lip it resides in on the top shell.

Although better than the " brute force method " one could still damage the lip and latch.

I am not saying I have perfected the method, but the method I have illustrated takes into consideration the lip and latch and requires minimal effort, just a little finesse.

The force used in the "push pull technique" you refer to is again almost extreme, unless you can leverage the bottom shell out of the lip in the top shell while pushing and pulling at the same time!

Wednesday, pub crawl, see you there, Geoff

P.S. clean the oxide of grit with a brush and alcohol. I then use a fibre glass pen with alcohol and top it off with a film of silicon grease for slide contacts

Edited: 1 June 2009, 10:59 a.m.


Geoff, I'd definitely order a copy. Having an e-book per series (i.e. one for Classics, one for Spices and so on) sounds like a good idea if the price is right.
How about including it in a future release of the MoHPC DVDs?

Joel Setton



Is there an interest in a 50 to 100 page book full of how to illustrations, before and after photos, labelled figures, tool requirements and restoration techniques with appendices including diagnostic programs for the 65, 67 and 97?

Geoff, my answer is Y E S . I will order a copy as soon as you will have published this book.

I read all of your excellent restoration postings and would like to own them in printed form.

By the way, including schematics of 65, 67 and 97 would be highly appreciated.




I want to make sure that the credits are given for various techniques, so I will be posting various descriptions of the techniques used.

I would appreciate help as to the original authors if possible. The archives here are fantastic and I will try to have at least most of the booklet done for HCC2009.

Of course the London chapter of the HPCC may get an early look also!

Cheers, Geoff


Repairing HP67
Repairing HP41C

Edited: 1 June 2009, 5:24 p.m.



There is one problem with the HP67 repair that you show. The epoxy fix for the motor to worm gear coupling effectively disables the clutch feature, which limits the torque that can be transmitted from the motor to the worm gear in the event of a card jam or some other problem that could stall the motor and damage it. Geoff has a fix using wire insulation that effectively preserves the clutch feature, while providing efficient transfer of torque under normal circumstances. Hopefully, Geoff will include his clutch fix in his repair treatise for the HP65/67/97/41 card readers.



As the input from any other interested members progresses, I will know who or whom to credit with the original concept.


I intend to document the most efficient/extensive repairs that have been created by the group as well as myself. To that extent, thanks for the links Saile! Each repair will be done by me (most have already!) and then assembled into the booklet so keep the links comming.


Hello Michael, the HP 65 booklet has already been created and covers 22 pages with full colour matched and labeled photos. In that repair the pinch wheel and clutch have been covered as well as PCB cleaning, contact cleaning, case restorations, diagnostics, battery holder surgery and etc.


I will include in the 67 section some basic differences to the restorations. The 97 will include printer restorations as well as printer and card reader removals. Since the roller and clutch are similar it would not be cost effective to show the same repair for the 67 and 97.


The HP 41 card reader is a different animal with respect to reaching the roller. I will show the steps for disassembly and reassembly of course. The same repair for the HP 67 et al will apply.

Also the HP 41C dissection will in itself be a large section covering as many of the differing keyboards to PCB connections that I can find. So far I have 3 differing PCB's, one of which (Singapore 1986 CX halfnut) does not even need any of the screw posts or screws at all to function correctly. I.E. a couple of elastic bands to hold the shells together!!!!!!

The 41C section will be an offshoot of the paper at the October HCC2009 conference.


The other families have their own quirks, but mostly it involves the safe separation of the halves; especially the latter LCD voyagers, pioneers and stretch pioneers as well as the spice documented earlier at the museum.


Section on keyboard repairs (non-invasive) and invasive techniques. As we know some keyboards are riveted in place and preclude and easy dissassembly. I have an 11C here in need of a new LCD panel so for the heck of it I removed the rivet heads to gain access. It works now, however it is time to find a final fix for the rivets, small screws, melted plastic, epoxy........


In conclusion

Now many of the repairs have been done before but again for the sake of consistency I will be documenting each repair step by step.

There will be two major repairs, the HP 65 and the HP 41. These will cover keyboard repairs, screw posts, connections, electronics, case restorations, label printing on home computer, label restorations.

The rest of the families will differ in access to the internal sections, keyboard differences, display differences, case restoration differences etc. In effect, this will be a differences section with a photo essay of diassembly of each family or series; photo documentation of fixes that would differ from the 65 or 41 section.

Cheers, Geoff


micheal, can you provide us the HP-approved value to which the torque limt should be set when repairing "THE CLUTCH"?
that would be surely of greatest help to all 67/97... restorators in the forum!



Bravo! I could not think of a kind way to state (once again) it isn't a clutch. Thank you for a most elegant way to prove that fact...


I found your original deleted reply much more than unkind. It was plainly rude and insulting. And the reply by Hans is sarcastic and arrogant. Regardless of the merits of your respective opinions, enlightened people simply state the reasons for their positions, and do not resort to personal attack. My reply to Saile above did exactly that, no less or more. I did not question his wisdom or intelligence. So, if you want to challenge my or anyone else's statements or positions, just do so factually without engaging in unnecessary vitriol.



Which was not my intent and why I deleted my original post as I felt the topic didn't warrant further comment. I think it was up for no more than a minute before I deleted it.

If you felt it was rude and insulting, that's unfortunate as it was only an expression of my frustration with bad information being propagated. Personal attack? I don't see any names mentioned or implied. Harsh, yes, but personal? Not in my view. Believe me, I did that once on this board a long time ago and I've never repeated it.

Since you've now seen fit to mention something not seen by everyone, in the interest of fairness, here it is again.

[begin deleted post]

... because if somebody tells you an HP card reader has a clutch, don't believe them. It is never referred to in the HP documentation as a clutch because it isn't one.

The lead screw and motor combo was a complete assembly and in a functional, factory original reader, the screw is quite firmly attached to the motor shaft. The "clutch" action comes from the card slipping against the drive wheel.

To anybody that says otherwise is only parroting what they've read on the Internet. The proof is the 97 and 82104A service manuals. So is the proper motor adjustment procedure. You don't just adjust the eccentric until the the thing works... Do you really think that's how HP did it at the factory?

It is amazing to me how much bad information is out there that just keeps turning up again and again. Very sad. Let's not propagate it any further here, okay?

[end deleted post]

I believe I now understand why David Smith no longer posts... :(


Aside from any frustrations with inaccuracies, urban myths postings and etc, the factually basis of the responses was the reason for the posting in the first place.

For example, the "clutch". What was the reason for the addition of the coupler from the motor shaft to the worm gear shaft:

1.  could the shaft and worm gear not have been one piece?
2. was the coupler in the form of a rubber sleeve been used as a
noise damper
3. was the coupler in the form of a rubber sleeve been used as a
vibration damper.
3. was it used to allow slippage for a jammed card, (since 1981
that has never happened to me and I use mine every day.

The 97 repair manual does not mention the reason for the coupling so urban legends are created. Also, not many of the originals designers around.

I have an HP67 new in box and the rubber coupler does not give, I haven't forced it! It is the original rubber, not glued or one piece. That has to lead to questions about replacement. Intuitively one would like to replace it with the actual material. In reality, that would lead to disintegrating rubber in 5 to 10 years necessitating another repair. That is why the 'insulation used as a replacement' idea was created.

The eccentric cam, as it is correctly called, yes it is adjusted after the system works although in C of the trouble shooting section figure 29 (refering to paragraph 4-40) it is used to adjust card reader speed.

Rotating the eccentric cam after assembly and with a reader that writes only or reads only has remedied many read/write problems, again, done by people after the repair and without manuals. On some machines the original rubber still functions, yes I have a 41C and HP 67 with functional original rollers. Both these had card reader read problems, not write problems. This may have been due the speed of the motor changing over time (lubrication?).

Randy and Hans, keep the 'Accuracies' coming, email me in person, better yet, write a small essay on the inaccuracies that you perceive are being perpetrated on the net and here. Post that in the articles section where it will not dissappear beyond the current page and maybe that info will be propagated. With permission I will add this to an appendix titled "truths" or something like that.

With respect to the word 'CLUTCH' you both are correct. There is no reference in the HP 97 manual to the CLUTCH, however, there is no reference to the motor 'CLUTCH' system. Even the exploded view does not refer to the more correctly called 'coupling' between the motor shaft and the worm gear. CLUTCH does appear, even if incorrectly, as the name given in popular literature.

This would probably mean the entire motor system was replaced as one piece and therefore did not warrant any mention of individual components, hence the made up name CLUTCH. Of course, I must say I have not read everypage of the 97 repair manual so if you could point out the reference to the correct name I would appreciate it. I will be calling it a coupling and still advocating an insulation repair which closely simulates the original properties of the the system. This may be a case where to much thinking has been applied to the system and this was the cheapest method to link a Swiss produced motor to a shaft at HP. That is, it requires no damping, slipping properties at all.

For Eric, I too, after a lot of research on the 'Internet' was led to believe it to be a 'clutch'. Although when I first saw the design, I was inclined to believe it to be a damper. It certainly removes vibration and noise from the system versus a 'glued' option which simulates a 'one piece axel'. My insulation replacement will much more accurately, in my mind, replace the design concept behind the rubber coupling. It can do that without knowing the 'reason or name' given to the disintigrated rubber coupling. But for the sake of the book, I want and need to be factual and therefore accurate.

There, the thread is back on track.


Edited: 8 June 2009, 2:02 p.m.



I used the term "clutch" only because it seemed to be common usage that everyone would recognize. In fact, it could not be truly a clutch, since a clutch is a device which gradually equalizes the speed between between a motor and some driven system such as a transmission in a car. A more appropriate description would have been an elastomeric torque-limiting slip coupling, which at some point would permit slippage between the motor shaft and the inner bore of the elastic coupling material. The slippage point would be determined by the tightness of the press-fit. Devices like this do in fact exist in the real world, and are used as safety-devices to protect electric motors from being stalled under power when some malfunction occurs such as a seized bearing. I assumed that HP had done this on purpose, whereas it now appears I was mis-informed.

I had absolutely no problem with Randy or Hans correcting me on this point; just the way they chose to do it. I have been politely corrected numerous times on this forum for my mis-statements, and will readilly acknowledge such errors without being offended. Suggesting that I or others are no more intelligent than a parrot is rude and insulting to me. Perhaps I'm a little too thin skinned to participate in a form such as this, where I may be subjected to such treatment dare I not do exhaustive research before posting my opinions.

Edited: 8 June 2009, 2:57 p.m. after one or more responses were posted


I agree with you, as explained below.

The Popular term is clutch for right or wrong. It would seem that I will need an appendix which translates popular terms to correct terms, unfortunately in this case, clutch, damper, or coupler may be the correct term and function!

The fact is the entire assembly was replaced and the manuals do not refer at all to the components! So as far as I am concerned clutch can suffice although I would add the damper and coupling terms.

I am awaiting more orignial info by mail from some of the period designers at HP. Of course I will also raise this in October.

As far as your postings, and any postings, information helps. Unfortunately we can never tell if sarcasm is nasty or humorous as we cannot read the facial expressions of the poster. I also missed the original posting that was edited so I missed the 'parrot' term.

I too think that with the above limit in postings, that sarcasm be kept at a minimum and corrective information be kept at a maximum.

Cheers, Geoff

Edited: 8 June 2009, 2:59 p.m.


There is one problem with the HP67 repair that you show. The epoxy fix for the motor to worm gear coupling effectively disables the clutch feature, which limits the torque that can be transmitted from the motor to the worm gear in the event of a card jam or some other problem that could stall the motor and damage it. Geoff has a fix using wire insulation that effectively preserves the clutch feature, while providing efficient transfer of torque under normal circumstances. Hopefully, Geoff will include his clutch fix in his repair treatise for the HP65/67/97/41 card readers.

I view that as a presentation of fact. Hence, my response.


As stated below in my response to Geoff, I have no problem with your statements correcting the facts....just the way you did it.


It would seem after careful reading of the 97 manual that HP replaced the entire motor assembly. Therefore they either:

a  did not think to add a design explanation to the coupling or
b the coupling is just that, a coupling of two components produced
at two differing sites that needed to be linked.

This fact coupled with the information that the motor was supplied from a swiss manufacturer and not specific for the HP designs MIGHT lead to the following conclusions (any original concept people from HP on the card reader out there? as it would seem everything else would be speculation).

1  melding an off the shelf motor with an in house designed system
would create an coupling problem for the engineer.
2 either ask the motor to producer to create the shaft - worm gear
as one piece or formulate a coupling in house.
3 since there are no specifications on TORQUE the assumption is
that it is not a 'clutch', the popular common assumption.
4 there is no mention of damping or noise suppression characters
either in the manual, this could be due to the fact that the
unit is replaced in one piece and therefore the design
specifications are not required.

Suffice to say, just because the TORQUE info is not supplied might just be an artifact of the idea that the repairer need not have the info as the entire motor worm gear assembly is provided as a replacement from the factory and the repairer need not know the parameters to affect a repair.

Again all this is speculating in a vacuum unless an original concept designer from the project can elucidate. I have a few feelers out there and am awaiting a definitive answer.

Until then the word 'coupling' may be appropriate although 'clutch' cannot be ruled out just because it is not mentioned in the repair manual. As stated this may just be as a result that the info was not required as the repair for the 'clutch' was a replacement of the entire "motor assembly" see table 6.4 of the repair manual.

Of course the assembly and component is mentioned in HP notes as a 'couple that dampens'. Oh well, who new!!!

Just a thought,

Cheers, Geoff

Edited: 8 June 2009, 6:30 p.m. after one or more responses were posted


Some background info from the patent hosted on Eric's site:

Some additional info here:

And the best description I'm aware, available on the HP labs archive:

Designing a tiny magnetic card reader Jump ahead to page 15.

FWIW, we could just ask the designer:

Bob Taggart, CEO & Chairman
Chaparral Communications, Inc.
San Jose, CA 95128


the info provided is helpful.

The way it was presented to me was also appreciated. The component is referred to as a couple in the patent with no explanation as to it's design intent other than joining the two systems together.

The second reference is great in that it explains the couple is used for damping (noise and/or vibration?)

So hence forth 'coupler or couple' is the preferred name. Unfortunately until information supplied by you and others (and will be referenced in the book) other words have been coined, not parotted, as they are in common usage. So an appendix or addendum would suffice to correct the terminology.

Cheers, Geoff



I have no problem with the name, only the continued propagation of the incorrect belief that the device is there to provide slip between the worm and the motor shaft. 'Nuf said.


I think for future reference that information be supplied, and that vague statements about 'torque' in this example (whether facecious or sarcastic or made in good humour) would be better off not made.

I am new to this restoration book idea, the reason for the posting was to solicit information exactly like that which you supplied, as opposed to the off handed statement made. That is also why it will be peer reviewed.

Now if the original statement had made about 'torque and the manual' and combined with the information you supplied of what exactly it is, then that would have been much more helpful and not have offended anyone.

Boeing 737

An interesting story (to me) was the coloration of certain subsystems on the over head panel of the Boeing 737. The colour scheme was dark grey with 4 subpanels being in a light grey. I asked an instructor of the import that the colour scheme. After getting several contradictory explanations about engine failures, generator failures and fuel switch cut off systems, I asked a Boeing representative. He stated he would make some calls as he did not know. 4 weeks later he called back and indicated that he had to call up an 87 year old engineer responsible for the colour design. It turns out that the explanations, over the years, from the experts was wrong. It had nothing to do with engine failures, fuel switches, hydraulic problems, power failures. It was infact, placed there to graphically indicate to the third member of the crew in 1964 (the engineer) which switches and systems were his pervue and not the pilots.

Within 2 years of the design, the engineer was removed as redundant but the colour scheme remains in place to at least 2005. Since no one was around all the explanations were created in a vacumn.

Cheers, Geoff



I would happily buy a copy (or two, one for keeps, one as "working" copy) of your book.

I seem to have accumulated (how did that happen? ;-)) quite a few calculators, a few of which are in need of some restoration or other.

One question: would you be doing further editions, for instance to include chapters on models not yet covered such as HP-48S/SX/G/GX (from your own experimentations or others)?




I'd definitely buy a copy!!




see below!

Edited: 4 June 2009, 8:00 a.m.


I'd certainly purchase one.


Geoff, consider publishing on CD or DVD, this would minimize your costs and allow easy video presentations. Regards, Sam


This will be a peer reviewed book, maybe by the HCC committee, but this can all be hashed out.

The book will cover the following:

chapter and title calculator for demonstration

1 classics 65
2 topcat 97
3 woodstocks 29C
4 spice 34C
5 voyager 15C, 11C
6 pioneer 42S
7 clamshells 18C (don't want to mess with the 28S)
8 HP 71B metal back and plastic back
9 charlamagne (48 series) 48sx
10 41C and card reader

some appendixes
dry box
battery pack
hints ideas
credits and citations
diagnostic routines (where they apply)

Since there is overlap in repairs and restorations the book will have a chapter dedicated to each family using the calculator given above as an example. Two chapters will be larger then the others; classics and 41C.

These chapters will entail all the steps for a complete restoration, for example the HP 65 is a perfect example of a classic plus some. The restoration of the full calculator inside and out including the card reader. Once the card reader has been described the only difference to restore a card reader in the 67, 97, 41C is in the access, which will be covered in the separate chapters that they reside in.

The 41C chapter is also larger as it includes problems such as screw posts, screw retainers, battery contacts. The card reader will be included here as it is very different in the access to pinch roller.

The other chapters will include the differences in access or keyboard restoration or any other difference that must be addressed to restore each machine.

The voyager will have two sections, including a non invasive restoration of keyboard, bezel and etc. The second section is a complete invasive restoration involving removal of plastic rivets for the keyboard and access to the LCD for replacement.

I am in London and have had a great time with Hugh Steers, thanks for the crawl (albeit short). When I get back I will post the actual table of contents. Most of the photos have been done so on to the text of the book and of course some more restorations.

Cheers all,


The DVD form might be included with the spiral bound book, have to think about that as the DVD could include many more colour photos. The book will be an "on demand publication" which will limit cost. It will include MANY explanatory photos and as few spelling mistakes as possible ;-)


Hello Geoff,

Great work.

I will send you my notes and pictures on he HP10 (the printer one) repair. Feel free to include in your book also.

All the best



Excellent! This will also cover the 19C.

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