Texas TI-59: A tale in pictures

[albertofenini]

Hi Jose,

where did you connect the scope to measure that wave ?
Any specific point at the head terminals or at the LM324 or at the 594 ?
thanks for help !!!

(11-15-2014 09:41 PM)jebem Wrote:  Marcus and Gene,
Thank you for sharing your past experiences and knowledge.

I started with a Casio FX-29 (or a 31, I don't remember the exact model) but moved to HP RPN machines as soon as I get money for them, having owned a HP-25C, a HP-55, and a HP-67.
Texas was the "other side" and only recently I have acquired a few of them, as part of my new calculator collection that includes only four brands so far (HP, Casio, Texas and Elektronika).


Card Reader testing - Part I
While I wait to get a good keyboard replacement for my HP-59, I had a closer look to the card reader and did some testing.

DC Motor:
DC resistance: 2 ohm

Current consumption without load (Tol. +/- 10mA):
41 mA @3.0 VDC
52 mA @4.5 VDC

Current consumption under load (Tol. +/- 10mA):
113 mA @3.0 VDC
130 mA @4.5 VDC

4-Track Magnetic Tape Read/Write Head:
Read/Write heads resistance (Tol. +/- 1 ohm):
L1: 270 ohm, L2: 272 ohm, L3: 265 ohm, L4: 267 ohm

Read/Write heads inductance (Tol. +/- 5 mH):
L1: 60 mH, L2: 60 mH, L3: 60 mH, L4: 60 mH

Signal output using several prerecorded cards of unknown state:
Signal read directly at the read heads with a oscilloscope (Tolerance is high here, like 10%).
Amplitude: 9 mVpp
Wave shape: Clean, it looks good to me.The encoding looks like a basic pair of frequency signals using FSK or maybe PSK (Phase Enconding), but I couldn't find information about it.
Higher period: 1.25mS (800Hz)
Lower period: 2.50 mS (400Hz)

According to the service guide, the magnetic head output signal is about 3 to 4 mV peak, so my readings (9mV peak to peak) are probably within the required values for a good card reading.



EDIT: Video showing the reading operation.