HP41 card reader weirdness


I recently acquired a plasmoid refurbished card reader. At present it works well with my halfnut 1987 CX. However, recently, it has been misbehaving on my 1984 fullnut CV--gibberish in the display, erasure or corruption of memory, non-response from keyboard, higher than usual rate of the "malfunction" message or checksum errors.

I have recently wanded in and used numerous programs with calls to synthetic registers (M, N, O), so I thought there was some monkey business there. But I use those same programs on the CX and there have been no issues either with the calculator or the card reader.

Most recently, the card reader won't even pull a card thru on the CV, though CAT 2 shows it is being "seen" by the calc. Fresh batteries don't seem to be an issue--I have swapped batteries between calculators too, and that makes no difference. I know that card reader per se is fine, since it works flawless with the CX.

On the buggy CV, other peripherals attached to port 4 behave normally--thermal printer, IR module, wand.

Could this be an internal connection issue--there is enough power to port 4 to render the above peripherals usable and for the calc to recognize the card reader ROM, but not enough to properly drive its operation? I know from experience how fussy the part that conducts information from the modules to the motherboard can be--it is held within by pressure only. But the calculator was completely refurbished by Randy last spring,and I don't think it has been dropped or harshly molested since.

And what about the power requirements? Should I fetch and try new batteries first? Is it possible that the same battery set in the CX (a newer machine) is adequate drive everything, but is not potent enough to power the calc and the card reader in the older fullnut CV?

Grateful, as always, for wisdom.



Most recently, the card reader won't even pull a card thru on the CV, though CAT 2 shows it is being "seen" by the calc.

Actually, I just rechecked and CAT 2 either returns nothing, gibberish, or the calculator freezes and I have to take out the batteries.

I have noticed that the more I play with the calculator the weirder its behaviour with the card reader inserted gets. Maybe this is related to battery drain?

I understand that the gold plating on the port contacts can wear off when a peripheral is repeatedly inserted and removed, and I do admit lately Port 4 has gotten a lot of use. However, I have two other peripherals and 4 modules and they all seem to behave normally when plugged into Port 4, as does the calculator itself--no display weirdness, freezing, gibberish, etc. The calculator just seems to have grown a recent dislike for that card reader being plugged into it.

According to CAT 2 on the (working) CX the Card Reader version is 1F.

If this is as simple as weak batteries let me know, but like I said I have pretty fresh batteries in both calculators and swapping the batteries between the two doesn't resolve the issue. Of course, if the older fullnut has a higher requirement, that could be my answer.



I have just discovered on the CX that even with the calculator OFF, inserting a card should activate the motor and pull it through even if nothing is read or written.

I move the reader over to the CV, and this experiment fails--no pull thru.

Also, now when I execute CAT 2 I get basically a line of gibberish then a CAT 3 listing (+, -, /, *, etc....)

I am guessing that it comes down to something to do with how the card reader is powered by the calculator. It could be something as simple as both of my sets of batteries being adequate enough to run things on the CX, but below threshold to power the calc and the card reader on the CV. I am worried that it could be something more sinister--broken or corroded contacts or circuits for example. But the calc has been opened up and serviced by one of our best just a few months ago. Also, as long as the card reader is not inserted, everything works fine, and port 4 functions normally with everything I have except the card reader.

If this is something that boils down to just batteries, I will be really embarassed after visiting radio shack tomorrow. But something tells me there is something else going on here beyond just batteries, unless there really is a big difference in current requirements between my CV and CX. It could be I may just have to use the card reader only on the CX if an incompatibility with the CV has occurred. That is a shame, since the CV, with its crisper display, is my favourite.



les, the card readeris a real blood sucker to the batteries. however, i think that even with new batteries installed you will have no luck. i am also of the opinion that the cardreader is fully intact. imho, the internal contact bridge of the cv (the block that holds the flex-pcb for the ports) is causing the problem due to corrosion or loss of pressure of the underlying elastic strip. i would try to take the cv apart and thoroughly clean the bridge and the contact pads on the keyboard pcb with isopropanol, and then re-assemble the cv.
cheers, hans


Since Randy reinforced things when he repaired it it was easy to take apart and get back together.

I cleaned the bridge and contact pads and gave the strip a little squeeze to round it out since it may have dimpled in somehow.

I also noticed that although the gold contacts on Port 4 don't look corroded, the edge looks slightly rough at the edge, like I traumatized it when inserting or removing a module. I tried to gently flatten down the rough edge with a thumbnail.

I reassembled, put the batteries back in, and after the calc took a few seconds to shake its head and wake up properly after the trauma, I was able to carefully attach the card reader and pass and read a card or two.

Thank you so much, Hans! I am going to get fresh batteries anyway....


Edited: 28 Jan 2007, 7:49 a.m. after one or more responses were posted


Actually, this adventure raises another question for me:

The card reader is a top heavy thing and I suspect puts quite a bit of force on its contacts. The little clips on the side really don't seem to bear much weight. I am wondering if it is sensible to keep the card reader in the calculator all the time (the extra space in the case would indicate this has been contemplated by HP), or whether it is wise to just keep it in to read and write cards, then immediately remove it. On the other hand, the risk of wear on the contacts for increased insertion and withdrawal needs to be considered too.

Really curious to know about this. When I took a look at that rough edge on the port contact, I came to appreciate just how delicate the innards of these things can be.



Hello Les,

Concerning your recent difficulties getting your HP-82104A card reader to work properly with your HP-41CV:

I would like to assure you that your rebuilt HP-82104A card reader will function equally well with HP-41C, HP-41CV or HP-41CX.

While on rare occasion it may happen that a given magnetic card is defective and will not properly record, when reading a properly recorded card, there should be virtually zero error rate, typically less than 1 error in 1000 passes. Unless you've gotten something sticky on your cards, your should not have trouble reading them.

Continuing errors indicate a problem with your calculator, batteries, or battery charger.

CAUTION: A defective calculator can scramble the programming on even a "write protected" program card. If when reading a card, the card stops suddenly and the HP-41 displays anything other than "LOW BAT", this is usually an indication of problems with the electrical contacts in your calculator. The calculator may display "MEMORY LOST", or a scrambled display, or the calculator may simply turn off. Furthermore, while a "LOW BAT" warning may be a true indication of weak batteries, it may also be the result of deteriorated battery contacts.

It is a common misconception that the HP-82104A causes a heavy drain on batteries. A properly rebuilt and adjusted card reader draws only a moderate current. In testing my rebuilt card readers, I will write approximately 180 cards and read them back 1800 times before having to replace the alkaline batteries in my test calcluator. For most users, this is less than a year's use, and for the overall health of your cacluator, batteries should be replaced every year.

Although it is possible for contaminants to foul the port contacts of an HP-41, this is usually not the cause of problems. The 'wiping' action of module/accessory contacts as they are installed tends to push dirt and other loose contaminants out of the way.

The most common problem with HP-41 calculators is deterioration of the gold plating on internal and external electrical contacts. The gold plating on the contacts can be lost through wear or corrosion, and once the copper substrate of the contacts has been exposed, it will oxidize to a non-conductive state.

The gold plating is meant to prevent oxidation of the copper substrate, but extended exposure to battery leakage will eventually exploit microscopic imperfections and undermine the gold. The gold plating on the battery contacts and the port contacts can also be worn away by heavy use.

Simply cleaning and/or polishing the contacts is only a temporary fix, as the exposed copper will again oxidize to a non-conductive state in a relatively short time. The gold plating must be properly restored. Note that for electrical contact purposes, gold cannot be plated directly over copper, as copper ions will migrate into the gold layer during the plating process, contaminating the surface.

As a final related note, and for the sake of completeness: Cracked plastic around the four screws that hold the two halves of the calculator together can also result in malfunctions similar to those caused by deteriorated electrical contacts. These are the screws located under the rubber feet, and they must hold the calculator together firmly at all four corners to insure the integrity of the internal connections.

If you send me your HP-41CV, I can restore the plating on the contacts.


Edited: 28 Jan 2007, 7:00 p.m.

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