HP-67 Card Reader became very touchy

[Alevin]

(10-20-2023 12:57 AM)teenix Wrote:  

(10-20-2023 12:09 AM)Alevin Wrote:  After reassembling, the light squeal some time was heard disappeared.
. . . .

May be the lo-batt condition reduces the card speed and these makes easier to read the card?

Regards

The squeal can sometimes be the lubricant at the end of the drive shaft has dried out and the shaft is rubbing against the ball bearing at the end. Some molybdenum grease can help, Tamiya brand in small tubes available at hobby stores.

It could also be caused by a damaged coupler causing the motor shaft to oscillate back and forth, or the bearings in the motor have worn.

Maybe the normal battery condition is causing the card to move too fast through the reader and the HP software cannot keep up with reading it. The only way to alter the speed is to change the motor speed resistor value on the sense board.

If you have an oscilloscope, you can check the read data and make sure it has completed before the motor switch opens. The bit width is approximately 1mS (1KHz).

There are some additional service notes for the card reader near the end of the HP-97 service manual.

cheers

Tony

Thanks for your kind and patient advise.

Certainly the time of the card passthrough the card reader is different when battery pack is full charge (about 1,9 sec) or low charge ( about 2,3). - I will compare with the transit time on Hp-67 (even though they are not exactly the same stuff). (In Hp-65 its much smaller, about 1,2 secs). In my Hp-67 card reader repair, the speed was easy to modify, as it has a potentiometer, but it did not made difference regarding the reading errors.

In any case, I am considering to follow to modifying the R1 resistance.

But previously I am thinking in remove and check again the capacitance of the recently replaced C6 cap, as I measure a very low capacity (7 pF ?) once installed in the Logic PCB. Is not this strange? May be it was deteriorated during soldering or legs are in short.

More over, the indicated diode (CR5) in the pic attached, tested on the board is conducting in direct (700 Ohms) and inverse polarization (1.400 Ohms). Is this correct? The same happens is measuring the resistance on diodes on the main PCB in the area of the card reader (CR1, CR2, CR3, CR4)

PD. The info about idle gear experience with bronze and plastic materials has been upload to
https://www.hpmuseum.org/forum/thread-15...#pid178849

Regards

Ricardo