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Musings and comments about our common interest


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HP 54501a oscilloscope

During this week end I have been beginning to repair our unit of HP54501a oscilloscope from the early nineties.

What a design! The main circuit and all the other circuits (keyboard, power supply, CRT driving circuits) are of exceptional design. The main circuit is built around a Motorola 68000 microprocessor, and the layout and the PCB itself are incredibly beautiful and well done. This is the quality of HP of that era, second to none. 

Also the clarity of the manuals and the accompanying documents is exceptional. You get a course on oscilloscope basics for free when you read them!

I will post updates as the repair go. Suffice to say that the self test information was extremely clear and conducive to an easy diagnostic. 

More on next issues...

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Time module in HP41CL


So far the hp41cl doesn't provide a clock to be used as time module, and it requires a working one to be able to function as stopwatch or alarm clock (or launching programs at a defined time)

However, the hp41cl "raw" provides all the time-related calculating functions of the time module: days difference between two dates, date calculations, etc. So, if you don't want the above clock features, you can live without it (and why would you want them when you have a smartphone?)

There are always those that would like to have the full Monty (never better said when referring to Monte’s development), and then you may want to have the time module too. Or, you have interfaced your hp41c with other items, and then you need to launch programs at a determined time intervals. 

I once did that, when I connected a HP3468A HP-IL multimeter to the HP41CL to check what was the voltage in my weekend cabin during an extended period of a week. Then it was grabbing data every half hour for the whole Monday to Friday we’re not there. 

Other uses that we’ve seen are: 

- use it in conjunction with astronomical programs, to better direct your telescope.
- Use it during flight to calculate fuel consumption rates, direction drift on side winds during time periods, etc. 

As always, here is no reason this couldn't be done with a smartphone - but if you don't have the program that does what you want, then the easily programmable HP 41CL can come to the rescue nicely.

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New connectivity and virtual Prime calculator software!

New Prime software issued in December.

You remember probably that we announced a beta version of new connectivity software, and also virtual calculators, with the advantage of introducing Mac OS versions of both. So, for those of you that were using Windows virtual machines to be able to make it work, you need to run to the ftp site and retrieve the new versions to have MAC OS native Prime apps. And they do work well!

The FTP sites you can download it from are:

Quoting from Tim Wessman:

The connectivity kit and emulator are now supported on both windows and mac. The iOS/Android/Winstore versions will be downloaded through your normal phone update mechanism as they are approved by the various stores.

HP Prime Connectivity Kit Installer - Windows

HP Prime Virtual Calculator Installer - Windows 

HP Prime Connectivity Kit DMG - macOS

HP Prime Virtual Calculator DMG - macOS

This release is focused around getting macOS support, and all the store applications synchronized. There were some changes in the Core calculator code, but mostly this will be identical to the last release.

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HP instruments coming

There are two items of the measuring area pending testing and cleaning:

A HP 54501A Oscilloscope. One of the first Digital Oscilloscopes by HP, with the quality of the past HP;

A HP 8591E Spectrum Analyzer. This is a very interesting machine, which many amateurs don’t have due to its high price. We’ll try to make a special price since we got a decent deal ourselves.

Also, there are many other items coming our way - including boxed, near mint calculators  - stay tuned!

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New HP41CV units!

We now have again two HP41CV units left, with all back ports and battery side cover. It is still a wonderful machine, that can be enhanced with peripheral and modules to a still competitive machine - not in speed but in functionality. And with the legendary HP keyboard click!

One unit is a full nut and the other is a half-nut: the newer design which is more reliable since it has fewer inner parts.

Price is 130 € plus shipment.

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More about: HP41cv
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New articles for this Christmas tree

We have received several calculators in good physical state that we have thoroughly revised and -when needed- repair.

Let’s list them here:

  • A HP41CV converted to HP41CL. Very nice physical status and completely new battery/back ports module
  • Same, but with a tall keys HP41C. Probably the best click we have  seen in a long time. Good tall keys are always better than normal keys in my opinion. Please email for pictures or more information
  • Two HP41cv machines. One of them is a full nut; the other is a half nut. Both are in very nice shape, with all back and side ports available.
  • Repair assemblies: nicely collated flex circuits onto original plastic inserts for battery-port contacts.
  • We also have memory modules, extended memory modules, math and stat modules (boxed!), a rare Home Management module, the powerful Advantage module, and many more goodies.
  • We also have a HP3478A multimeter that works well and still keeps the battery strong. 

We’re also preparing a HP 54201A Oscilloscope, for which the data battery died and we’re soldering a new one, good for 30 year more, and a HP 8591E Spectrum Analyzer, for which we’re doing a thorough testing - so far it seems to be working well. It is an amazing machine, that you can interface through HP-IB to your (old) computers. Please drop a line to to get more information about our measurement items.

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Calculator repair - spare parts


I have been spending some time in trying to learn 3D printing creating software, in order to create calculator pieces. In Shapeways, there are already several parts for the HP41c and other HP calculators. Look for designer davef, who has designed several parts for our calculator: back port doors, side battery doors, battery covers and other HP71b items. However, these never have exactly the look and feel of the real thing - they could even be considered nicer, but not the real thing.

But there is no need for nice finish for internal parts! So I am looking forward to create a piece that can be used in the innards of the calculators. You need to destroy - or abandon repair - a calculator to repair another, and that’s a quite expensive way of doing it! The price in Europe for defective HP41c is around 75-85 EUR. So any effort to create parts that help keeping in shape our best tools is welcomed - but it sure takes time for someone not used to it!

By the way, this is the Shapeways' HP spare parts site:

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Calculator repair - Adhesive conductive tape

Continuing with the repair thread we initiated 3 issues of this blog ago, we go now into the adhesive conductive tape. This is the description I get from the 3M page:

3MTM Electrically Conductive Aluminum Tape 3302 is a 2.0 mil (50 micron) high strength dead soft aluminum foil coated with specially formulated conductive pressure sensitive acrylic adhesive system. Good adhesion, malleability and adhesive conductivity allow for extremely low resistance and make this an excellent shielding tape. Designed to meet a wide variety of EMI and RFI shielding applications in the electronics industry. Also for use in printed circuit manufacture and repair.

Cut in small pieces, it can be used to cover the eroded parts of the battery contacts. Please remember to remove all oxide with Caig De-Oxit first; in some cases, the conductive film of the circuit will be destroyed in the contacting part, and there comes handy the conductive aluminium tape. You need to cover the whole contact, to maximize the electrical transfer area. Nacho thinks that it also needs to look good: a proper repairer will cover all four contacts, so that it looks coherent and symmetrical.

It also can be used in other circuits to create aground plane, and also for shielding. Every repairer should have this in his toolbox.

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New Prime Firmware beta!

I downloaded yesterday the public beta versions of the HP Prime apps. For the first time there are native Mac Os apps! A connectivity kit, virtual calculator and prime firmware (although the latter is the August version and therefore no new)

My personal computer is a Mac, while my company’s is a PC running Windows 7. My company has not jumped yet to Windows 10. I had the connectivity kit installed in my PC and also in a XP virtual machine in the Mac (actually, the best XP I have ever run, regardless of machine)

You can get information about the beta in the site:

For me, it is fantastic; but we stress the fact that it is a beta, and not a finished product. We (and HP) cannot take any responsibility about what may happen to your Prime and computer (although it doesn’t have a new firmware for the Prime itself)

And for those who were upset of not having a solution for Mac - well, you have it here! and it works much faster than the standard program on the PC

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Corrosion on battery contacts


The assembled repair kit is a drop-in part for damaged-corroded battery contacts in the hp41c family of advanced scientific calculators. It solves the main issue that plagues old 41c units.

There is a cheap alternative when the damage is minimal. There are times when there is not too much corrosion, or where friction has caused the black support to appear (meaning the metal has disappeared in the contact area, but it is still available around). In these cases, there are two material that you need to know: Caig De-Oxit and the adhesive Aluminium paper.

Caig is an American company that produces several liquids to clean metals. I have been using its compounds for my hi-fi hobby for a long time - the sound and image really improve when you clean the interconnect contacts with De-Oxit; and they are maintained in good condition (and the golden or nickeled contacts preserved from dendritic corrosion) with Caig Pro-Gold.

Well, Caig De-Oxit works magic for removing corrosion. Use it with cotton sticks, rub them gently on the corroded part and you will see how the corrosion dissolves.

I have been using it recently on several deep corrosion cases on hp41c. Not only the battery assembly was corroded beyond repair, but also the circuit lines were completely green. As the battery assembly circuit had been destroyed by corrosion, the only solution there was the repair kit; but for the main calculator circuit, a generous application of De-Oxit led to a completely clean machine that worked from the first second it was reconnected. I must say that I have also failed with other calculators, but that may be due to additional damage elsewhere.

Tomorrow I will show to you the adhesive conductive film


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