HP-67 Reads cards but does not write

[Trevor Gale]

(02-13-2024 09:47 PM)teenix Wrote:  With the switch leaf contacts, they should all be above the circuit board by the same distance. It is easy to try and adjust them and they become uneven. I'm not sure if the CRC chip is upset by this and causes R/W errors.

The short motor on time is due to the software. This usually happens when an error occurs, and the motor can speed up and run for a short time just as the card has passed through. As this seems to have occurred after you tried adjusting the switches, I'm wondering if this is due to the way the switches are adjusted, maybe it comes back to CRC timing.

The capacitor that seems to give card problems is marked on the diagram. If you decide to change it, then as John kindly mentioned, you may as well do them all.

The R/W head might need a cleaning also.

A couple of assembly tips,

When reassembling, make sure the keyboard assembly sits properly in the calculator before tightening the 6 screws. Sometimes the black plastic frame is not sitting properly (can rock back and forward a bit) and warps when tightened. This may affect the card reader.

Check the wiring at the top of the keyboard. These can fray if the disassembled calculator is moved too much and may limit battery current. My Classic Notes, page 44.

Lastly, be careful with the Power and Prgm/Run switches. The golden contacts can fall out causing a short on reassembly and when the battery is inserted can destroy the display Anode or Cathode drivers. I found this out the hard way.

cheers

Tony

Thanks again, Tony, for spending the time with all my queries.

I checked the tantalums with an ESR meter I have (also measures ESR at high frequencies so it's not just a cheap 'Eastern' box!) and they were okay so I put them back in circuit (I have to re-order a batch of components to refill my workshop 'spares'). I also re-checked the 'goldfinger' (sorry for the pun, I couldn't resist!) contacts for height and operation and they are okay.

I re-adjusted the eccentric spindle just a little again, and now this HP-67 *WRITES* fine, every time, but it will not read!!! It will not even read the card that it has just written - but it did write the card perfectly (on 2 different cards I tried) as they are perfecly readable with my HP-97 machine, both cards.

It is a kind of puzzle I have not encountered in many years of experience with the HP-67, HP-41's that I have - I'll admit that I have not yet put an oscilloscope on the CRC chip to check data waveforms but I somehow doubt that that would give me a good clue as to what is happening... after all, if it writing okay then it should be able to read the card especially one that has just been written by the same head in the same machine under the same conditions... Any more ideas?

Kind greeetings - Trevor.