HP-41 Card Reader - HELP


I have a card reader and it seems fine mechanically, it pulls through the cards and does not leave any messy deposits on them.

However after appearing to record a file it will not verify and I always get CARD ERR immediately.

It does the same on both my 41CV nd 41CX.

I don't know if it is not recording or not reading the cards as I have not got any recorded cards.

Can anyone help by offering to send me a pre-recorded card with a small program on it? (I am in England). I can then at least check if it reads ok.

Also any other offers of help to diagnose the problem are welcome. I am an electronics engineer and could pull it apart to check signals on the record head etc, but I want to do as much diagnostic work as possible before dismantling it. I do already have the excellent repair articles which have been published on this site.




Let me get to the problem. Forgive-me if I ask a silly question: what are you doing, so you record data in a magnetic card? When you mention record a file on it, you mean any of the possible data - program, registers, status or all information? Or an specific data type?

The CARD ERR appears anytime you attempt to read or record or only when reading? I have not seen CARD ERR when recording cards, only when trying to record on bad magnetic cards.

Did you try the VER (verify) function?

I'm an Electrical Engineer, and I just want to focus on the possible problems.

Best regards.


Hi, here is a clearer explanation:

1. I write a small program onto a card, this looks like it works ok.

2. I try to verify the card XEQ VER, but as the card starts to pull through the reader I get CARD ERR.

3. Same thing hppens on both calculators 41CV and 41CX.

4. I have tried it several times with different new cards.

5. I have no known good recorded card to check that the card reader can read ok, so I do not know if the fault is when writing to a card or when reading a card.

6. I would like to check the read capability with a known good card before I try to dismantle the card reader.

7. I could also send a card I have tried to write to someone with a card reader to find out if the card has written properly.

Thanks for any help...



After the description, I must agree with David. He is right (he's been right since the beginning; I was the one who did not understand the problem): you should disassembled the reader. I have done it myself for at least five times; it's a safe procedure, be confident and check for the contacts and capacitors. I have not done it yet, but I'd do it, based on our experienced contributors' (valuable) guidance. In fact, I have done so many things based on them, the last one being the upgrading to 32K RAM in an HP42S - Thank you, Randy! -, that I'd do without hesitation.



Two possible problems:
1) One of the switch contact springs is not working (probably unlikely, the design is much better than the HP65/67/97)

2) Readers that write but do not read are almost always caused by a defective tantalum bypass cap on the reader chip power supply. It is usually a small blue dipped tantalum that has developed a high ESR. It usually tests good, but replace it anyway. There are two other caps on the read head windings. They are probably OK. Some readers have a fourth tantalum. It is probably good also.


Dave, thanks for your help.

As soon as I can check if it is the read or the write which is faulty I will change the capacitor as you suggest.


Apologies for not replying sooner... I am in the UK, and have a working HP41 system (with card reader). I would be happy to write a couple of cards for you and post them. Or I can see if I can read cards that you've written on.
Are you in the LOndon area (or can you get to London)? If so, then there's an HPCC meeting in London on the second Saturday of each month. I would be happy to meet you there and look at your card reader (I have repaired several of them, and I normally have a reasonable toolkit with me at meetings).


Hi Tony, thanks for you kind offer.

I am in Liverpool and very unlikely to be able to get to one of your meetings, though I would like to!

I will email my address to you and then we can exchange a couple of cards to see what happens.

I have just partially dismantled the reader but I am stuck at the moment because I dont want to try to remove the circuit board without some further advice from someone (like you?) who has done this before and learnt the hard way.

But I will put the unit back together (minus top cover) to write a card and then try to read yours.

Regards, Gordon.


My view is that you should never use 'lucky dip' methods of faultfinding/repair and that at this point you haven't collected enough evidence to decide if a particular capacitor is faulty or not. However, I can tell you how to take the thing apart.
I assume you've got the top cover off, which means you've peeled off the label unnerneath.
Next, unclip the cover over the HP41 'plug'. It's cliped firmly on at the sides, but it can be prised off. Then undo the remaining 2 screws underneath the label. Everything then comes out of the case -- the mechanism and 3 PCBs.
The PCB on top of the reader mechanism is held down by 3 screws and plugs onto pins coming from the mainboard. It contains the switch contacts and part of the write-protect optical sensor.
The PCB at the back contains the (custom) sense amplifier/LED driver chip. This is the same as in the 67 and 97, where the latter section is used as a motor controller. Note down the wire colours for the head wiring first (these wires just push into contacts on the PCB). This PCB is pluged into edge-connector-like contacts on the mainboard. It can be removed easily, but make sure you align things properly when reassembling.
The main PCB contains a DC-DC converter and 3 chips. The largest one is the card reader interface. One of the others is an HP41 ROM that contains the card reader control firmware. And finally there's a 555 timer (!) for motor speed control.
IT's a pity you can't get to the meeting, as I'd have been more than happy to take it apart there and then and check signals with you (I have a LogicDart...). Oh well.....


Your help is very much appreciated, and if I could get to the HPPC meeting I certainly would. I agree that I should diagnose the problem before doing anything and if you are willing I will continue to use email to try to pinpoint the problem.

Thanks, Gordon


Hi Tony,

slightly off-topic,

Does the LogicDart have an HP-48 display?
The display resolution seems alike.




Hi Dave, if you email me I will be able to reply to you and attach a picture of the card reader. I have added an arrow pointing to the cap I think you mean, but I would like to check with you that it is the right one before trying to change it. Also, can you give me some advice on the best way to remove the psu board?

Thanks, Gordon

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