Repaired HP-97 card reader doesn't show any signs of life


Hi all,
I'm trying my hand at completely renewing a very battered - but working - HP-97 I had.
I managed to get everything going fine (actually it got it to be very nice looking) except for the card reader.

After repairing the clutch, cleaning the mechanism and putting the o-rings, it simply doesn't work, at all. It does not even try to start.

I measured the voltage coming from the ribbon cable and I get about 6V from the 1st and 3rd ribbon. So, the calculator is providing energy to the card reader. Also, the printer advance mechanism (the button on the right side of the printer is not connected, but I think that doesn't have absolutely nothing to do with this).

Any ideas? At least on how to check if the card reader is not simply dead? I remember there was a post some years ago about the voltage that could be measured in the printed circuit board of the card reader itself to test it, but I can't find it anymore.

Edited: 14 Feb 2013, 10:24 a.m.


This is the proper HP test method to test the card transport operation (from the service manual with my additions):

Start by verifying the motor works. Unsolder both motor wires from the circuit board and apply 3 vdc to the motor (red is +).

With no card, the no load current should be no higher than 50 ma. A good, well centered screw will run quietly at less than 20 ma. Anything higher than 50 ma is cause for investigation, the usual cause is the lead screw is off center or is not seated fully on the motor shaft. If the unit squeals, a small drop of plastic safe oil on the lead screw socket will usually fix it. This can also be a bad sign of motor bearing noise which I will not address here.

Now, allow a card to feed partially into the reader and grab the card and hold it. Adjust the eccentric for approximately 200 ma with the card stalled. If you cannot get the current under 300 ma, there is a problem - usually the rings are too large. The normal position is for the dot on the eccentric to be at the twelve o'clock position with the card path being right to left.

Once you know the motor works and eccentric adjusted, re-attach the motor leads to the board. With power off, measure resistance between the common point (PC hole closed to the M test point) and the PC locations marked M F H. They should be > 10k ohm.

Manually push a card into the reader leaving 10 mm exposed. This will put the card in position to activate all three switches. Measure resistance again, this time each point should measure less than one ohm. Most likely, you M contact is not closing correctly which why your motor does not turn on.

If a switch is not closed, remove the circuit board and carefully clean the board contact areas and the leaf switch ends. Remove the card and re-insert, this time watching for the switch ends to move upward as the card contacts the balls and push the switch(es) up. Re-assemble and re-test.

If you *must* adjust the switches, understand how they work so you do not do any damage. Turning the adjustment screws clock-wise raises the switch end. Since they are all on one plate, they do interact with one another. Remove the board again and adjust all screws counter-clockwise until each screw just touches the plate. Re-attach board and re-insert the test card. Now, start with the M test point and adjust the screw closest to the M point clockwise until the switch closes. Repeat for the F and H points. Remove the card and insure each switch is open. Re-insert the card and re-check. A change of just 1/8 of a turn is typically the range for each switch to close and open correctly. Be patient, work slowly making small changes until all three open and close properly.


Thank you Randy!

I can't get past the first steps though.
I took the motor out plugged it to a 3V battery and it did work indeed.

After re-solding it to the mechanism... nothing. No mater how much I try to put the card in and play a bit with the screws, there is absolutely no activity from the motor.

I've measured the resistance between the contacts in the + and - of the motor and it gives 12.5 ohm.

Also, can you tell me where to measure the current you talk about: "With no card, the no load current should be no higher than 50 ma"? Where should I measure this? And with the calculator plugged on and the card reader connected to the ribbon?


Do the switches operate correctly?

The current stated is the motor current. Measure current in series with the motor when it is connected to the 3 vdc power supply.


Hi Randy,Hi everyone,

sorry for jumping in this thread, but I couldn't resist asking a few hints on the HP65 card reader, and generally speaking about the HP card readers from HP65, HP67 and HP97.

I'm in the process of restoring an HP65.

I'm able to read a standard pac card, usually at the second or third try, I don't get any error message when I try to write on a blank card, but in no way I can get to re-read the card I have written.

What can I check ?

Could it be because of the eccentric badly positioned ?

Can you please post a picture of the eccentric ??

I read a lot about the positioning of the eccentric and I understand it plays a role in successfully restoring a card reader, but I can't figure out how to set it properly.

thanks again to everyone and sorry for jumping in



There is no magic for card reader rebuilding, one only has to follow the procedure in the HP97 service manual on the MoHPC dvd set.

The eccentric is set correctly when the motor draws 180 ma +/- 20 ma with a card that has been partially fed into the reader and then held so it is not ejected.

Did you use o-rings or tubing for your 65 repair?


Thanks Randy for the reply,

in this case I have used tubing, but I have the same problem with
other units, HP65 and HP67 where I have used o-rings.

I will measure the current values, are they the same than those of an HP-97 card reader ?

I understand the eccentric is the white nylon part, which remains almost hidden once the card reader is -reassembled.

I'll be on a busness trip till tuesday, but I will try to post some more pictures when I will be back.

My problem is that I can read pre-recorded cards (rarely at the first try), but I cannot get reader to write my onw cards.

This is pretty much the same problems I have on all the units where I have changed the gummy wheel, both with o-rings or tubing
thanks a lot for help, Alberto

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