HP-67 Card reader calibration – fine tuning



#6

Hi everybody,

Sometimes, I’ve troubles with my HP-67 to write on the magnetic cards. I guess, the “blanc card corner” contact is not very well tuned. Maybe, I must screw a little bit something in the golden plate inside the card reader, but what? Maybe could be a dirty contact or a broken soldering. Any ideas?

TIA,
Albert


#7

Hi, Albert;

I'm not sure if they are EXACTLY the same, but I had my own HP97 card reader with problems (the HP97 itself was a gift from an e-friend in Spain). In this case, after turning the calculator ON the card reader tried to pull a card and, after about one second, it stopped with a big error message in the display. I disassembled it and checked the thin golden plated 'blades' (is there a better name for this?) and saw that the one that senses card presence/insertion was touching the circuit board, as if a card was inserted all the times the calcualtor was turnned ON. I 'tunned' the sensing 'blade' by visual checking only, just leaving the smallest space between them and the contact in the circuit board while there is no card inserted. As there are three contacts I assume that the first one is for 'card insertion' and the other two are for 'card position' (ready to read/write) and 'protected card'. In all cases, they are closed one at a time when a card is being pulled.

I'd try to actually see if the distance between the golden-plated blade and the contact in the circuit board is the same as the other ones, and also if there is no dust on any of them. I have already disassembled many 82104A (HP41 card reader) and in this case the contacts have no adjustment, but I remember having one of them with bad-contact problems because of dust. My own HP97 card reader I didn't need to disassemble so far.

Please, let us know what happens. Also, wait for others to post; better ideas come from different places, and it's wise to be aware of as many as possible prior to go ahead.

Hope you succeed!

Luiz (Brazil)

Edited: 27 May 2005, 2:35 p.m.


#8

The procedure for setting up the 97 card reader is in the service manual, available on the MoHPC CD-ROM.

Basically, there are 3 contacts -- card inserted (to turn on the motor), card-at-head (to start reading/writing) and corner-clipped. The leaf contact has 5 screws through it, The 2 at the edge hold the contact in place (and should be tight), the other 3 each adjust one of the contacts.

IIRC the procedure is to connect a continuity tester (Ohmmeter, etc) across the PCB connections for each contact (with the reader fully assembled), screw in the adjusting screw until the contact just closes, then back off a specified amount (something like 1/8 of a turn)

That's fine for the 97, where you can get to the reader and the adjusting screws with it assembled. It's not good for the 67, where the contacts are on the keyboard PCB, and you can't get to the adjusting screws with it in place. I've found a good basic setting for the 67 (and 65 which is much the same) is to screw in the adjusting screw until the contact finger just starts to lift.

If necessary, push a card through by hand (or with the motor, disconnected from the PCB, running from a bench supply) and check the contacts switch correctly. YOu can find the connections on the keyboard - logic PCB pins, see my HP67 notes for the pinout (or get the HPCC schematic :-))

Before adjusting anything, clean the contacts _and the pads on the PCB_. Clean them with propan-2-ol and with a pencil eraser if necessary. I had a 97 reader that would not set up properly which turned out to be due to dirty contacts.


#9

Also, adjusting one contact will affect the adjustment of the others. You need to check the adjustments other repeatedly as you tweak each contact. The HP41 reader design was changed to get around this problem.


#10

There should be minimal interaction between the adjustments -- I've never found it to be a problem. I would check that the 2 fixing (as opposed to adjusting) screws are tight, and that there's no dust, etc, between the leaf contact and the reader chassis.


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