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HP 67/97 Card Reader - Dreato - 04-30-2021 04:46 PM
There are 4 nylon ball / reed switches used to control these card readers. 3 are identified - motor, heads, write protect. What is the 4th one for??
Thanks and Regards,
Dave
RE: HP 67/97 Card Reader - teenix - 04-30-2021 11:44 PM
(04-30-2021 04:46 PM)Dreato Wrote: There are 4 nylon ball / reed switches used to control these card readers. 3 are identified - motor, heads, write protect. What is the 4th one for??
Thanks and Regards,
Dave
The circuit layout on the May74 Journal Fig5 Page 6, shows a 4th switch as a motor inhibit, but I guess they decided they didn't need it. This was probably connected to the MI pin on the sense chip, which is tied to the switched battery voltage, so the motor is uninhibited. Same issues for the 67. The 97 looks like the MI pin has a delay before being switched high. Maybe the motor started briefly at turn on without it.
The circuit board pad that this 4th contact finger connects to goes nowhere so I guess now it is a spare part after you lose one of the others.
cheers
Tony
RE: HP 67/97 Card Reader - Dreato - 05-01-2021 12:10 AM
Thanks, Tony. Good information! You've relieved me of some of my ignorance.
Regards,
Dave