HP-82104A Card Reader Repair Questions

[Hiwi]

Hi,
i always dismantle the reader and apply 3 V to the motor. I disconnect the cable to the PCB.
Then I measure the current. It should be about 200 mA. All from 180 to 240 should be fine.
When a card is inserted.

Before I adjust the idle current to a minimum, the worm gear should rotate smooth, the motor mount has influence on the current. Try to get it to a minimum. I suppose you have all cleaned thoroughly (the head, the roller etc.) and put a very small amount of lube (Mos2) on the gears and bronze bearings. The worm gear has a clutch, which has to be firm.

Then put a card in the slot and measure the current.
The card should be drawn evenly through the slot. If the silicon tube is too soft or not adjusted exactly (centered) the card does not go evenly through the slot. You can hear this.

Adjust the axle to the correct current. It is not a rocket science, the range is wide.

Try some more cards, because they have not all the same thickness.

This is all from the mechanical side. Tony has made a nice guide called the classic notes, you will find some very useful hints there.

I have replaced only very seldom tanatalums in the HP41 card reader. There is a 6.8uF tantalum on the sensor board, which may be faulty. But it is not a general solution for card reader problems.

On the bottom PCB, there is a small potentiometer, this would be my last advice to adjust the speed a little bit, try only with small rotations.

Double check all connections, measure the resistor of the maghead coils.

That is all for today :-)

Ralf