HP-67 - 1612A03018 - Card Reader Advice Requested (was HP-67 - strange behavior)

[albertofenini]

Hi everyone, we have split the thread in two separate threads.

This thread will be about the restoration of the chassis 1612A03018 that originally had
a bad CPU board.

We substituted the board with a working board received from a donor, and we have tested
three types of card reader.

Out of the three card readers only one was found "compatible" and was the one HP-67 style
The other two, were HP65 style as can be seen in the pictures.

We have played a little with the variable resistor but it is very sensitive and at one point it was not
reading nor writing anymore, so we stopped playing ...

It also must be noticed that is the only card reader we have rebuilt we square o-ring, and even
in the past HP-67 restorations we have done it was the only way to make it work,
as both round o-ring or single piece of rubber didn't work out well.

We have also replaced the three capacitors on the card reader pcb and the one on the motor.

Now we are stuck at this point :

Reads well one sided cards
Write (well) one sided cards

Read well two sided cards
Write (apparently well) two sided card (we have been successfully only once)
but when we read back a double sided card, it goes well on the first side,
asks for the second side but is sounds "slippery" in the meaning that accelerate toward
the end of the reading of the recorded second side and gives an Error message.

What could it be to make the unit behave like this ?

Pictures and clips are here : HP-67 - 1612A03018

P.S. it's only us or also your bench looks like this at the end of a working session ?

(10-20-2019 03:17 AM)teenix Wrote:  Running from the battery does not provide any speed regulation, it will run as fast as the power available lets it.

The card reader has speed regulation built in so as to compensate for fluctuating battery voltages during normal operation.

This is controlled by the 4K64 resistor. Have you tried testing the value of this part?

Putting a 10K variable resistor may help. I am not sure if the speed input to card reader chip can handle directly to ground or battery so may be wise to keep the variable resistor set around mid way.

Also, I have heard replacing the 6uF power filter capacitor with a tantalum one can enhance the motor operation. The small cap on the motor terminals might also be a problem. I think it also is part of the control circuitry for speed feedback, or maybe just for filtering.

The 67/97 card read/write can deal with slow or fast cards up to a point. As long as the data fits on the card within its limits it should work. The 65 is different as the data transfers have to be sync'd to the CPU but may still work with different card speeds, but again, up to a point.

cheers

Tony

cheers

Tony