HP 65 - another card reader problem [Solved]

[AndiGer]

Lately I received a nice looking HP 65. Seems to work fine but the card reader.
I replaced the gummy wheel by O-rings. The card passes thru nice but with a squeezing sound (a thing I sometimes also have with a second unit that reads quite well).

But the real problem is the card in the reader seems not to be registered as the display doesn't turn dark during the card running thru.
It accidently happened to me with the second unit that there was an error when reading a card with blinking display: When I put the card into the slot during blinking display to my surprise it ran thru but no dark display as well.
So I conclude that a card is passed thru the reader when the motor switch is turned on with no regard of the calculator is in error state or not. Pure physical pass-thru of the card is just determined by the motor switch and the running motor without regard the calculator being in "ready-to-read" state.

Am I right here? Any similar observations anybody?
Any suggestions what to look for? (Currently no oszilloscope available.)

Traces of the card reader PCB are ok. Only two minor oxidations that do no harm to the traces, 0 Ohms measured.

[cds]

Hi there!

The symptoms you describe ring a bell for me ...

I hope to remember the details correct:
There are 3 contacts in the reader: One to detect when a card is inserted, one which detects the card beeing in reading position, and the 3rd to detect if the card left the reader again.
There should be also 3 screws to adjust them. Make sure all of them open/close as expected by cleaning and/or adjusting. Just use a simple multimeter to measure them.

Regards

Carsten

[AndiGer]

Hi Carsten,

Very good idea! Yesterday I disassembled the calculator and although looking clean I cleaned all the golden tongues of the reader and their counterpart on the keyboard PCB. Checked the contacts with a MM and were fine.
Today tested it and the card reader works! Although the cards give a squeaking sound when run thru.

Did not yet test writing :-)

Andi

[teenix]

(04-07-2019 03:16 PM)AndiGer Wrote:  I replaced the gummy wheel by O-rings. The card passes thru nice but with a squeezing sound (a thing I sometimes also have with a second unit that reads quite well).

It may be possible that the O-rings are slightly larger than the original wheel diameter and the eccentric cam might need adjusting to reduce the pressure on the card as it passes through the reader.

cheers

Tony

[AndiGer]

Will give it a try soon - and report
Andi