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41CV Card Reader Repair Problem
Message #1 Posted by John Smith on 2 July 2003, 8:43 p.m.

I recently tried to clean the gummy wheel. Old gummy rubber sleeve has been replaced by fuel line tubing. Appeared to be same OD and ID. Tube was carefully placed on the spindle with a small drop of superglue on the spindle. There was no excess glue leftover. Allowed ample time to dry. After reassemble to the system, now I'm getting the MALFUNCTION message. It pulls the card beautifully. Initially I used to get "weak battery" complain, now I don't see that complain any more. But when I take the card reader out of the calculator, I don't get that "weak battery" message at all. Few times that I saw when the card reader was attached to the calculator. Is it possible that batteries are NOT strong enough to drive the card reader, but still OK just for the calculator alone? If so, should it cause card reader to display MALFUNCTION? Or, is the card reader completely toast?

Before I discard that or auctioning out as out-of-order product, I need your help. Is there any hope left for me to further repair this unit?

Perhaps, you can provide me step by step diagnostic procedure, or maybe outline the steps for the process of elimination.

Please rescue me at your earliest convenience. Thanks.

Edited: 2 July 2003, 8:46 p.m.

      
Re: 41CV Card Reader Repair Problem
Message #2 Posted by Vieira, Luiz C. (Brazil) on 2 July 2003, 9:58 p.m.,
in response to message #1 by John Smith

Hi, John;

first of all, DON'T throw it away! AFAIC, MALFUNCTION is caused by many reasons, but this is a card-reader exclusive message.

Quote:
Is it possible that batteries are NOT strong enough to drive the card reader, but still OK just for the calculator alone? If so, should it cause card reader to display MALFUNCTION?

If you have the card reader owner's handbook, have a look at page 51 and you'll see it's possible to happen. But if you simply insert the card reader and switch calcaultor to ON and you see BATT (low battery) indicator lit, than there is something wrong.

If it is actualy toasted, it is more likely to freeze calculator's operation (not even turnning it to off is possible) or not allowing it to turn ON. I had one that is probably turnning around the globe and it used to disrupt calculator operation. After plugging it in and switching calculator to ON, it was necessary to remove batteries because it was not even able to be turned OFF again.

Possible problems are scratched or magnetized head, open coils inside the head (this is impossible to repair) or bad contact somewhere (small daugtherboard, head wires). Also, check if wires are in correct order (I once did it and thought I lost my working unit...). Mechanical problems are more likely to force motor and produce strange noises; as your card passes fine, it is not an issue. Oh, yes; there are two small "flat springs", like metal strips (cooper?), one that alignes the card and another presses it to the head while it is pulled. You should check if they are correctly settled.

If you need more advice, let us know.

Success.

Luiz - (Brazil)

            
Very elegant causes
Message #3 Posted by Mike on 2 July 2003, 10:27 p.m.,
in response to message #2 by Vieira, Luiz C. (Brazil)

No offense but these are very elegent causes. It still amazes me that people always look for the more exotic causes before looking for the more simple causes. It's a Engineer thing, I guess.

I have a degree in Engineering and also have worked as a technician. I find this same phenomena with some of my Engineer coworkers when they try to troubleshoot electronics. They come up with the most exotic possible problems before looking for the simple ones. I always say, "look for a simple cause before lookig for a comlex cause."

In all the readers that I have ever repaired, I have never found any of these possible causes, to be the cause of any reader problem that I've tried to fix. Doesn't mean it's not possible but I've not seen them and I've repaired over 100 readers. The most likely causes of dirty head or bad cap or misadjusted eccentric isn't even mentioned.

My suggestion:

If there is no reason to believe the reader was bad and all that was done was to replace the drive rubber, then the most likely cause of problems are related to something you did. Possible causes 1) dirty head, 2) misadjusted eccentric or 3) contact problem.

If the reader was already bad, regardless of the drive wheel, then look for other problems. Bad capacitors can cause problems. I doubt very seriously that the head wires are in the wrong place, unless the person doing the repair remembers pulling them out.

Malfunction simply means the reader thinks the hardware is broken. Could be just about anything but start with the simple causes. I have removed these problems with as simple a step as adjusting the card tension.

                  
Re: Very elegant causes
Message #4 Posted by David Smith on 3 July 2003, 10:29 a.m.,
in response to message #3 by Mike

A dirty head or bad head wiring almost always causes the "CARD ERR" message and not MALFUNCTION. I would check the card sense leaf springs, the internal sense LED, and the reader to calculator contacts. Also make sure the motor is installed properly and is engaging the drive gear properly. Also the worm gear tip should be in its little hole.

                  
Re: Very elegant causes
Message #5 Posted by Gordon Dyer on 3 July 2003, 4:56 p.m.,
in response to message #3 by Mike

My card reader gave the CARD ERR message and it turned out to be an open circuit coil in the magnetic head.
Luiz helped me get a spare head from another reader which fixed it.
Is this very unusual? (I mean the fault, not Luiz help!!)

                  
Re: Very elegant causes
Message #6 Posted by Vieira, Luiz C. (Brazil) on 3 July 2003, 6:37 p.m.,
in response to message #3 by Mike

Hi, Mike; thank you for your comments.

Quote:
No offense but these are very elegant causes.

Iím not offended. (is the term "elegant" offensive somehow?)

Quote:
It still amazes me that people always look for the more exotic causes before looking for the more simple causes. It's a Engineer thing, I guess.

Iím an electrical engineer, and Iím not offended at all.

Quote:
In all the readers that I have ever repaired, I have never found any of these possible causes, to be the cause of any reader problem that I've tried to fix. Doesn't mean it's not possible but I've not seen them and I've repaired over 100 readers.

Iíve repaired three myself and helped others to repair I-donít-know-how-many; youíre experienced, thatís good.

Quote:
The most likely causes of dirty head (...)

I assume, maybe wrongly, that if someone has already opened the reader, removed the gunk, replaced the gummy wheel for O-rings or fuel tubes and tested it, then the head has probably been cleaned. If the card causes CARD ERR message when reading, I ask him to clean the head.

Quote:
(...) or bad cap (...)

I knew that bad caps could cause problems in card readers after reading some posts in here.

Quote:
(...) or misadjusted eccentric isn't even mentioned.

As I mentioned in another post, I used to think the exocentric was not to be touched. Anyway, as we have O-rings and fuel tubes, adjusting pressure is necessary. Also, I believe measuring current drain when pulling cards is an important reference to adjust the eccentric, do you agree?

Quote:
Malfunction simply means the reader thinks the hardware is broken.

This I did not understand. I used to take [MALFUNCTION], maybe wrongly (again), as generated by the firmware when the reader as a hole was not working properly.

Thank you, Mike; thoughtful and reasoning considerations are always welcome. I did not write this post till now because I did not have the time to elaborate the text.

Best regards.

Luiz (Brazil)

Edited: 3 July 2003, 9:47 p.m.

      
A simpler suggestion
Message #7 Posted by Renato on 2 July 2003, 11:11 p.m.,
in response to message #1 by John Smith

I would check if the fuel line tube used is not dragging the gear by rubbing against the inner sides of the gear case. I had that problem (low battery message) when i used two o-rings , but did not glue one ring to the other. As one slipped away from the correct position, it rubbed against the case - I guess it caused too high current drain.

It is possible to test card transportation by connecting a regular AA 1.5V battery to the motor terminals. I tried this, and could check for a smooth card transport before reassembling the inner parts.

Good luck and have fun.

Renato

            
Re: A simpler suggestion
Message #8 Posted by Stefan Hauschild on 3 July 2003, 3:00 a.m.,
in response to message #7 by Renato

The most common error during my repairs was a high current through the motor because of wrong o-rings or fuel line. If the pressure is not correct it may transport the card but the motor drains a higher current than normal and may go with external power connected (I test my repair before reassembling with external voltage to the motor) but not with power from the internal battery. The other reasons for errors that are mentioned often (misadjustment) never occured during my repairs because I only remove the two screws from the motor and try to clean the system and to replace the wheel from the top. Maybe I was lucky and the head wasnīt too dirty.

Good luck and best regards

Stefan

                  
Accepted average current drain??? (edited)
Message #9 Posted by Vieira, Luiz C. (Brazil) on 3 July 2003, 6:28 a.m.,
in response to message #8 by Stefan Hauschild

Hello, Stefan;

I thihk your approach is very interesting. Based on your figures, what's the acceptable curretn drain when the reader is pulling a card? I do not know if you have the figures in both situations, but I thought about both cases:

1- a 1.5Vcc battery directly connected to the pulling assembly (no electronics connected, just the motor) and
2- the complete set: calculator plus reader

When you measured current drain you probably did it with the complete set, right? Hve worst and best case, or average measurement? It would help (me) a lot.

(Added later:) As we a dealing with particular measurements, reading operation would be better than writing when measuring card-pulling current. If writing is considered, an extra small amount of current will be drained to record data.

Thank you.

Luiz (Brazil)

Edited: 3 July 2003, 6:44 a.m.

                        
Re: Accepted average current drain??? (edited)
Message #10 Posted by Stefan Hauschild on 3 July 2003, 10:30 a.m.,
in response to message #9 by Vieira, Luiz C. (Brazil)

Hi Luiz,

I did not make any current drain measurements. An indicator for higher current consumption for me was the "Battery Low" Indicator on an HP97. If the batteries are good and you only run out of power when pulling a card the motor draws to much current. Then I connected the motor only to a regulated power source and saw a significant increase of current consumption short before the system gets stuck. When it is stuck it takes more than 1A at 1,5V.

After disassembling/reassembling all was fine.

Perhaps when I have to refurbish my next card reader (there is one HP97 in the queue) I will make some exact measurements.

Best regards

Stefan

                        
Re: Accepted average current drain??? (edited)
Message #11 Posted by Ellis Easley on 3 July 2003, 10:46 a.m.,
in response to message #9 by Vieira, Luiz C. (Brazil)

Luiz, please read the extract from the PPC Journal v13n9p11 that I sent along with the HP41 rechargable pack schematic. It says 170 - 250 mA is the "average" current drain with the card reader motor on, with peaks of 1000 mA. Also it has a good explanation of why alkaline batteries can't run the card reader when they still have plenty of life to run the calculator alone.

                              
Thank you both, Stefan and Ellis...
Message #12 Posted by Vieira, Luiz C. (Brazil) on 3 July 2003, 12:10 p.m.,
in response to message #11 by Ellis Easley

Hi;

I repaired at least three card readers (gummy whell problem) after getting in contact with the HP Museum folks; before that, I had no clue about how to do it. All of them got ready and working 100%, but I was not aware of the fact things could be bad if pressure was too high or not enough over the pulling cam. I saw the excentric since the first time I disabssembled one card reader in the 80's, but I thought that one was for production-line adjustments and never touched it. If I reason about it, maybe I would find the reason.

Excessive current drain or sloopy card pulling action may be directly related to this adjustment, if the pulling gum "replacement" succeed. So, measuring current drain when card is being pulled is one good reference to adjust the excentric and make sure the card is being pulled and there no excesive pressure that will stress the small gears and fastly consume battery poewer. If More than, say, 250mA is measured, then it's time to adjust the excentric or to check for something else that may be wrong.

Thanks, guys; now I'll do that every time I get an 82104A reader (if any) to repair. Very good points, indeed.

Luiz (Brazil)

      
Re: 41CV Card Reader Repair Problem
Message #13 Posted by John Robinson on 4 July 2003, 3:06 a.m.,
in response to message #1 by John Smith

Hi John,

I have exactly the same problem with one of my readers, but I do also have a good reader. I swapped the mechanicals (motor, slot etc. ) as a whole from the good reader to the bad reader to find the bad reader still had the problem. I therefore deduced that the electronics in the bad reader was cactus.

If you discover that "MALFUNCTION" is due to another cause, I'd love to hear about it.

Cheers, John


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