HP-65 goes on hold after reading a card

[Kostas Kritsilas]

(11-29-2020 07:49 AM)teenix Wrote:  

(11-29-2020 06:50 AM)Kostas Kritsilas Wrote:  I was told it was probably the read/write head or the wiring to it was at fault when I sent it out to have it repaired. The motor comes on, and pulls the card through well, it just doesn't read anything. All the keyboard functions work, and I can type in and run programs. Even though the card reader is pulling in the card, the display does not show any data has been read.

If you want to sell a spare read/write head, please let me know what you want for one. If you are willing to attempt a repair, please let me know what you would like to charge for that. I would very much like to have the calculator fully working, but cannot, due to vision issues, do the work myself.

You didn't mention card writing, but if it is the coils inside the head, (which would not be repairable), then I would assume the card cannot be written too as well, as these perform both read and write functions. The same for the external wiring to the sense board. If one is broken, then a read or a write will not succeed.

If it is the external wires, I'd be pretty sure like [kby] says, that the wires will most likely be broken where soldered into the circuit board, which is due to moving the board around too much putting stress at these points on the wires. Should be easy to spot and easy to fix. This is also a problem with the power wiring at the top of the key/display board.

For the same reason, it might be possible that the wires break at the point where they enter the epoxy in the R/W head. Repairs of this nature might still be possible, but a bit more fiddly as you would have to carefully dig the epoxy out around the wire end, solder wires back on and put more epoxy back on to secure them.

Hopefully all data checks were done with an oscilloscope to prove that the data is not actually appearing at the sense chip inputs and outputs.

cheers

Tony

I don't believe that the person attempting the repairs used an oscilloscope, as his background is in chemical engineering. He said he did inspect all the traces going into and out of the card reader ICs under magnification, and said they were fine, and verified them with a multi-meter.

He had some spare HP-65 card reader parts, and said that he tried to repair the unit with them, but then found out that the spare units themselves were bad. he also said that he would be putting his own spare HP-65s up on eBay as non-working units. he also said that the HP-67 heads are better in this regard, as they use a thicker, better insulated wiring between the board and PCB.

This is all I have on the repair process. The statements about the read/write head being bad, whether it was the leads going to the head, or the head itself, came from the person attempting to repair the unit. I can forward the relevant emails in direct messages if anybody would like to see them.