Texas TI-59: A tale in pictures

[albertofenini]

Hi Jose

Thanks for your reply
Will try to replicate and see what happens
But if it was disconnected how did you power it up ?
Take care Alberto

(03-26-2021 06:46 PM)jebem Wrote:  Hi Alberto,
I can't remember the exact procedure after all these years, but after reading my posts, I am quite confident that those readings were taken in open circuit, no load at all on each coil, when I was testing the motor and checking the coils impedance values, when the card reader assembly was disconnected from the main PCB. So I must have connected the gnd terminal of the scope probe to one coil wire, and the input scope probe to the other coil wire, checking each one of the four coils for a reading.

[jebem]

Hi Alberto,

I use a laboratory variable voltage power supply for that. These equipments can be bought at low cost these days at hardware electronics shops. My latest acquisition from a local shop goes from 1v to 15vdc and current limiting from 2amp to 0.1amp if my memory serves me well.

But you may take measurements in circuit as the internal impedance of the coils is very low compared with the imposed load of the input network used in the amplifiers. A small decrease in the signal is expected, as long as it is not much smaller than the nominal values indicated in the service manual.

[EdS2]

(11-15-2014 09:41 PM)jebem Wrote:  EDIT: Video showing the reading operation.

Just to note and capture a comment on that video:

Quote:George Carlson
10 months ago
The card used 4 tracks per side, four a total of 8 tracks. It recorded 2 bits at a time. Two of the tracks were for one bit, the other two tracks were for the second bit. For each bit there was a one's track and a zero's track. A flux reversal in the one's track indicated a one, a flux reversal in the zero's indicated it was a zero. In this way the data was self clocking and the card could be read at almost any speed. I was the guy who designed the machine TI used to write their pre-programmed cards. But that was a very long time ago.

[albertofenini]

Thanks to everyone !

I had seen that video, the original post is a very good reference for restoring the TI-59
The author, Jose, did a also a wonderful one for the SR-52 and thanks to that guide we have restored few SR-52

We usually do HP-65s and HP67s
In that case, we measure the resistance of the head coils and then we connect the card reader
to the main logic board

Also those heads have 5 cables, a ground (black) and a 4 colored cables, which are the ends of the
coils and these are connected to the amplifier into what is called RA, RB, WA, WB
which I guess stands for read channel A, read Channel B, write channel A, write channel B with
few capacitors there as well, all in all very similar to the TI architecture

To see what's wrong, when the calculator does not read or write , we look at waves between one of the 4 channels
and ground, not between the channels themselves (I don't know if I made myself clear)
based on those waves we can understand if the amplifier has a problem or what's is going on when
a card is passing thru, whether si for reading or writing

i was expecting the same here, that why I was surprised
nevertheless we will do some tests and publish the results

thanks again to everyone !
take care !