HP-41cx Card Reader rebuild question

[wheagy]

[attachment=1172]I'm rebuilding an HP-41 card reader due to the "gummy" deteriorated card feeder roller. It's working about 50%, but I'm having an issue, I think, with the part (small metal tab) outlined in red in this pic.
http://imgur.com/Q2QhwMy

This piece is flopping around somewhat loose and I'm not sure how it should fit. It appears to ride right above the read/write head when the unit is assembled, but I'm not sure if it's supposed to touch the head, hover just above it, or something else. When this part (metal tab) is in the plastic assembly, and I plug the reader into the HP-41cx, the reader motor immediately starts running, even with the HP-41 off, and eventually (after about 5 sec) just stops running. In this case it also will not allow the HP-41 to turn on either. If I leave the piece out of the plastic assemble - remove it), it seems to write a card, but when I try to read, I get a "CARD ERR" message. The piece does not appear to be electrically connected to any other part of the reader, so it seems like it might be for tension? But I'm not sure why the card reader mostly works when this piece is removed but not when it's installed.

Can anyone tell me the function of that part and how it should fit in the plastic housing?

Thanks,

Win

[Bill (Smithville NJ)]

Win,

Your post is a repeat of your post of Nov 1. There is no need to re-post questions. While I know you are eager to get an answer, double posting does not increase your chances of getting an answer and may actually discourage people from responding to you.

You may need to wait several weeks for the right person to read your post and have an answer. Other times, no-one has the answer.

Please give it a little time - not everyone here visits the forum on a daily or even weekly basis.

You may want to delete your earlier post and just leave this thread.

Bill

[jjb299]

OK, I just rebuilt one of these a few months ago and I remember that small metal tab. I recall it definitely sits loosely when you have it apart like that, but I forget exactly how it's supposed to fit when put together. I believe that tab lifts up when a card is inserted to bridge a circuit on the other side of the black plastic piece (again, I'm fuzzy on the details). However, the answer on how it operates might be in that black plastic wheel directly underneath the metal tab in your picture. Depress the black plastic wheel to see how the metal tab is affected. It should lever up the metal tab somehow. Put the white circuit board over top of it to see which circuit line its supposed to hit. You may have the metal tab in the wrong way as it is shown. Don't know for sure. Sorry for the vague answer.
-Justin

[wheagy]

That helps a bit, but there is no small wheel associated with that tab. The wheel below it lifts a metal contact on the other side of the plastic housing (and that contact connects to the circuit board. This particular tab, however, does not seem to be associated with any kind of electrical contact, except that it might touch the read/write head when no card is inserted. There's nothing on the other side of the plastic housing except a small piece of the tab...and this does not seem like it can contact the circuit board in any way. There does not even appear to be any contacts on the circuit board around this tab. It's possible something else was connected around this tab and it fell off when I disassembled the reader, but I don't remember seeing anything.

Thanks,

Win

[wheagy]

Here's one more follow-up. This pic
http://imgur.com/ZcUMjv0
is the other side of the plastic housing. The red oval marks the other side of the metal tab from the first pic. The blue is the other side of the small wheel below the metal tab. The green on the circuit board is the approximate location where the metal tab sits below the circuit board. There appears to be no contact with the circuit board..the circuit board sits about a 1/16" above the plastic housing. The long metal contacts that are moved by the small wheel and tab inside the card slot, seem to function normally and are not mechanically connected to the small metal tab in any way.

Again, for some reason, when that metal tab is in place, when I plug the reader into the HP-41, the motor begins to run for about 5-10 sec, then stops...even with the HP-41 turned off. If I take the metal tab out, the reader functions the way you would expect and appears to write cards, but I get an error when reading (could be that they are not being written properly I suppose). That small metal tab is a bit of a conundrum!

Thanks,

Win

[Bruce Larrabee]

Try this... If you look between the switch pcb and the switch plate you can see the two contact switches. With no card inserted the ends of the switches should be making contact with the pcb and nowhere else.

The switches have a little dimple down a little ways from their ends. Now, slowly insert a card. As you do the switches should rise up and the dimple should make contact with the pcb. This is what makes the motor turn on and off.

Okay that is a simplification, there is more to turning the motor on and off.

But by watching carefully you can see if the switches are functioning properly. They often are not. (For example getting stuck and doing something like you describe...)

If they are not working properly it is often because they have become bent or distorted. They can be repaired by being (carefully!) bent back to their original shape.

I'll try to check back and see if you have it fixed....

[wheagy]

Bruce,

Yes, I did check the longer "reed" type switches that are activated when the card slides through the track. They seem to function properly as far as I can see. They appear to be, however, completely separate from the small metal tab that sits above the read/write head. This tab appears to have no electrical connection to anything. My guess its that it provides pressure on the card as the card slides over the read/write head. The problem is that when this tab is in place, the card reader motor runs as soon as it is inserted into the HP-41cx (even with the 41 turned off). If I take the tab out, the card read appears to function correctly (motor only runs when card is inserted) but I get errors when trying to read the card. So I'm pretty sure this tab needs to be in place, exact when it is there, the unit does not work.

Thanks,

Win

[Bruce Larrabee]

Win - I think you are right about the card wrap spring (hp's name for the part you refer to) not having any electrical connection etc. And I can't explain why it would cause the reader to come on and stay on.

My advice is to check the action of the switches with a meter (assuming you haven't done so) to make sure the are not becoming stuck on. They almost have to be. And it's an easy test to make.

I mean if it's a mechanical problem this should determine that. And if it is electronic then at least you can investigate that.

I'm having a hard time imagining that the card wrap spring is causing this but then I've seen stranger things.

[Rsponholtz]

Did you have any luck tracking down your issue? I seem to be having a similar problem with my card reader: http://www.hpmuseum.org/forum/thread-4927.html