HP-67 Card reader woes



#5

Greetings all.

I have a 67 that appears to have some modest issues with the card reader. I spent the weekend trying to get the old girl (fella? seems like a sociology study) working again, and only met with limited success, and so I am hopeful that someone can help me further it along or help me decide if I need to send it off to fixthatcalc to do his magic on.

The problem is that the card is only pulled 1/2 way through, and then "error" is flashed on the display. By pressing Clx, the error message is cleared, and the card is then pulled through the rest of the way - indicating to me at least that the power is adequate for card performance. Thus far, I have examined a couple of other culprits:

1) The golden fingers may be bent too far. This is possible, however I am not sure; i) what they do and, ii) what the amount of bend is that they need.

2) I did not replace the sticky wheel, and I am not sure if this is the problem or not. I thought that the previous owner had done so, and this is why I did not pursue it with greater vigor. This will be the next step.

3) I noted also that the card reader head is very worn. It may be that the large number of cards it has seen may have had some negative impact upon it. Is there a way to tell if the card reader is within specs?


#6

The symptom of 'Error' after starting to move the card is very often due to problems with that finger contact.

To answer your questions :

1) The finger contact is lifted by plastic (nylon?) balls as the card moves through the reader. The ends of the fingers touch contacts on the back of the keyboard PCB.

There are 3 balls and thus 3 contact fingers. One lifts as the card is inserted to turn on the motor. The next lifts when the card is over the read/write head, and starts read/write. The last detects the cut-off corner of the card (it lifts later if the corner is cut) and is used for write protection.

I believe that if there's bad contact on these 'switches' then you get the 'Error'. In other words if one opens too early, or makes and breaks again due to too little contact pressure or dirt, you get thise problem.

2) You could try disconnecting the motor from the card reader PCB (note the polarity!) and run it from a 3V battery or similar. If that will pull the card through, the roller is probably OK.

3) There are ways of detecting wear in a magnetic head (often you
notice the drop in self-inductance of the head winding as the gap
gets worn larger), but I have no idea what the 'right' value for
a 67 head would be, or how far worn it can be before you have problems.

Over-use of the cleaning card will wear the head (to the extent that I never use this card, I take the machine apart and clean the head by hand). I've never found a head too worn to work, though.

I would start by cleaning (propan-2-ol, and if that doesn't work, a careful rub with an ink eraser) the contacts on the keyboard PCB and the ends of the finger contact. If that doesn't help, look at the fixing screws for the finger contact. The 2 at the end are for fixing it and should be tight. The other 3 are adjustments for each
'switch'. Try screwing them in _slightly_.

#7

Forgive me this simple quesion, but do you use a fully charged battery? I have similar problems when using the cardreader with AC adaptor and empty battery pack.

#8

If your drive roller has not been replaced, this could easily be your problem. While you have the mechanism apart, clean the head (and any other gunk in the reader) with isopropyl alcohol.


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