Hp-41C card reader - dead

[teenix]

(05-21-2022 09:46 AM)Vintage63 Wrote:  I have also discovered that all the cables are not solderd onto the various PCBs but they are inserted in some sort of plugs. I have checked them and they are all plugged in correctly.
What does trigger the motor when the card is inserted?
Cards are inserted from the right, correct?
Not that inserting them from the left changes anything either.
Thank you
Marco

A lot of HP calculators had this arrangement, I guess for servicing. I doubt you would find connections like this these days. The only trouble is that they can corrode and give poor connections, but I think this is mostly due to the effects of battery corrosion which is not a problem in the reader module.

There are 2 contacts in the reader, one detects the card insertion and the other is for starting the read write process. There is also an optical sensor for the write protect switch.

If you don't have it already, this is the circuit for the HP82104.

http://www.hpcc.org/cdroms/schematics5.0...p82104.pdf

This will allow you to see the switch connections and if you have a multimeter you can test them when the card is inserted.

Insert from the right, and the card should feed out of the left side. It will make a difference because the switches are on the right side of the R/W head.

If you look at the connection holes in the PCB top, imagine them numbered left to right 1 - 5.

As you push the card in pins 4 and 5 will short, then as you push the card in further, pins 2 and 3 will short just as the card touches the drive wheel. The first one starts the motor running, the second starts the read write process. The write is allowed or inhibited depending on when the optical LED detects the card. This will occur later if the card is write protected with the corner cut off.

The card processes are controlled by the CPU chip on the circuit board. There is also a small ROM chip for the CPU instructions. Obviously if these are faulty the module won't work. You said the 41 displays correctly, so maybe the CPU is working.

There is also a motor driver based on a common 555 timer IC (1826-0180). Some of this circuit may be faulty also.

An oscilloscope can help with fault detection.

cheers

Tony