Guess what I found

I had one of those, and was very fond of it. My third HP41 gave up the ghost a few months ago--I'll have to get another one at some point.

Cheers

Phil Hobbs

My HP35 cost $400 new. I still have a couple of them that work. That was, to me, the best calculator ever. Somebody should clone it with a uP inside. The "new" HP35 is awful.

I have three HP9100 desktop calculators, the predecessor of the HP handhelds. They are amazing, RPN with a CRT display, all discrete transistors inside. I'd like to get them working, but HP still refuses to release the schematics. So these historic machines are going into dumpsters.

These days I use HP 32SIIs mostly.

--

John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

You sure no-one wants to buy/collect them?

NT

Is this the original?

Mikek

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This email has been checked for viruses by Avast antivirus software. 
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I think I still have my old "freshman in college" HP-25 sitting around in a drawer somewhere... badly in need of a refurbished battery pack, of course, but the last time I used it (many years ago) it still worked.

Perhaps the trickiest part would be finding somebody to do the mechanical aspects of it properly.

IIRC, those HP hand-helds had the *best* key design I've ever used. They had nice crisp positive feel, and the legends were actually injection-molded *through* the keys and wouldn't face even when the keytop wore down with use.

A guy at my college dropped one of these HPs while walking from the dorms to class during a snowstorm, and the calculator was gulped by, and spat out by a giant-economy-sized snowblower clearing the Quarter Mile. It survived without damage.

One of my most compute-intensive projects on the 25 was the programming of an algorithm to calculate pi... iteratively. It just churned away for hours and hours and hours... :-)

I've got one of the "new" 35s, that I traded an excess slide rule for a few years ago. It's better than nothing but it doesn't hold a candle to the feel of the original.

That's it. LED display, pmos logic, wonderful key feel, all the right stuff (like pi) in plain sight.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

A wonderful calculator!

I still have mine, but no battery pack. I modified it to use dry cells. Works great.

I still have the manual and programming sheet.

I'll never give it up.

Good find and very good price. I collect old HP LED calculators (and a few LCD type): Hmmm... very old photos. I'll fix that when I have time. I think I have about 50 assorted working HP calculators, and an equal volume in parts and pieces.

Is it an HP25 or HP25c (continuous memory)? Not losing the program when powered off is a useful feature.

I suggest you dive into: if you need info and parts.

Schematic:

Battery packs are commonly available on eBay at outrageously high prices: The cells are just common AA size NiCd cells. If you want to roll your own, there was someone selling 3D printed clones. I'll see if I can find it again.

Chargers are difficult to find, but not impossible. The power supply is just a 10v AC xformer. It is prone to breaking the wires at the connector.

Please do NOT use alkaline cells or run the calculator with the NiCd batteries removed. Both methods have a higher voltage and might fry the calculator.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Sorta. Notice the "Hewlett Packard 35" printed on the front end of the keyboard. The originals did not have the "35" on the label: I have two of the most recent versions (with most of the accessories, docs, and packaging).

I use an HP35s and HP12c in the office. At home, an HP41c and HP48s.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

I bought an HP-45 my Senior year of college (1973) for $400. It still works, though the power switch is flaky. I've bought replacement batteries for it a few times and have a couple of "frames" that take standard NiCd AAA cells for it.

Which HP41? 41C, 41CV, 41CX, or 41C option 001?

A problem is the flex ribbon cables require case pressure to maintain contact. It usually appears as button failures or garbage results. The fix is to open it up, reinforce the stripped out screw posts, clean up the mess, and put it back together. It's NOT an easy fix.

Also common is the card reader craps out due to rubber decomposition. I've repaired about a dozen using a cut section of vinyl tubing as replacement. This is for an HP65 drive gear, but the HP41C should be similar:

A more serious problem is if you push on the epoxy blob covered IC's (Chip-on-Board) on the display PCB. That's fatal and there's no easy repair.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

I modified the battery pack and replaced the dead nicad AAs with NiMh. Works ok but I'm worried the charger may overcharge the newer batteries so I only charge them an hour when dead. Is the original HP charger ok to use with NiMh batteries and leave on charge overnight?

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I had an original 41C from 1979 (my Dad served on the board of Dillingham Corporation with John Young, then chairman of HP, so I got what I think was the first one in Canada--still had to pay list price, but I had bragging rights for about two weeks). When that died, about

1995 (after a hard life), I got a 41CV, and then about 2005, a 41CX.

This one died from a display problem--lots of missing segments, and gentle pressure on the relevant points didn't help.

The card reader needs some TLC as well.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Inside the HP9100:

Perhaps you might reconsider and have it repaired when you see what they're selling for: I believe that yours will easily sell even if not working. Here's a possible buyer: The HP Museum lists the value of an HP 9100 as $750 to $1700 and as "very difficult to find".

Diagnostic card:

I would normally volunteer to fix or buy them but I currently don't have the time, cash, or space. However, I'm curious. What's wrong with them? Display, power supply, keyboard, or computing errors? The big electrolytic in the PS are almost certainly in need of replacement, which might fix many downstream problems[1]. I fixed a

9100b that was the victim of condensed cigarette smog. Everything sorta worked, but not reliably. All the pots and switches worked erratically. Fortunately, the keyboard was unaffected. I had to give it an alcohol shower which was both messy and risky.

[1] Don't toss the electrolytic cap can. Remove it, clean out the guts, save the insulator, shove in a smaller new electroltyic, and replace the insulator. It will look quite stock if done correctly.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Nice. I got mine in trade for fixing several HP65 calculators, all with the infamous decomposing rubber drive wheel problem. I expected to get just the calculator and power supply. Instead, I received those, plus a large collection of ROM's, a large box of documentation, HP-IL printer, memory cards, programs, books, etc.

HP41 service manual with schematic:

Yeah, that happens. The easy fix is to just replace the display board. The problem is that there are several different types, not all of which are interchangeable. I probably have at least one spare, but no clue if it works or is the right type. See if you can identify yours: (Scroll down to "HP-41C Versions") and I'll see what I can find.

Repair is rather difficult. The ribbon cable is "bonded" (glued) to the LCD glass with some kind of acrylic glue doped with metal plated compressible spheres. Under the microscope, they look like about 20 micrometers dia. If the glue cracks, it's tricky to re-attach without the right type of glue. I've done so-so by adding a slab of rubber to add pressure. the problem is that if I take it apart later, the rubber will take a set, not land in exactly the same place, and cause intermittents. All my attempts to re-glue have failed. Some clue what this conductive glue is called and where to get some would be useful.

At least that's fairly easy. I just replace the decomposed rubber roller with my home made vinyl clone. In the HP41, the clutch also fails. (Scroll down to where the photos start in Message #7).

I would normally volunteer to fix it for you, but I'm overloaed and burned out from a 3 month battle with a string of kidney stones (actually sand). Bug me in a few months if you still want them fixed.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

I have no idea, Bill. Maybe someone else knows.

For the past 8-10years I have NiMH cells in my HP-67 and HP-35 and use the original HP slow chargers without problem. I believe slow charging NiMH is permitted but they cannot stand continous low-rate charge as NiCds did. So I tend to limit charging periods to less than 24 hours.

piglet

If you open up your HP-45, you'll probably find that the on-off switch contact fingers have worn two grooves through the gold plating and into the PCB. For rework, I filled the grooves with silver solder, smoothed the surface with a dental scraper, and piled 3 or 4 layers of gold leaf on top of the solder. Handling gold leaf is tricky so please find a web page with instructions first. I think I added some grease, but I don't recall. 15+ years later, it's still working on 3 calculators.

You can see the contacts at: They're the 4 vertical pads below the IC on the left. The PCB in the photo looks almost new, but you can see where the 2 grooves would be. Don't try to bend the contacts on the moving part of the switch. They're very brittle and will break easily.

You might also be lucky and just have some grease turned to tar on the switch: Be sure to read further down on how to remove the edges of the bottom aluminum label without permanently destroying it.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

There is an app (free) on Itunes and Android marked that uses the ROM file from the old calculators and emulate the calculator. So no need to go around with one, just use the smart phone

Droid48:

Cheers

Klaus