HP 65 Card reader task

[teenix]

(01-27-2024 07:51 PM)jftman Wrote:  Ok.
How does 6v appear in these places?
Given that Vss and Vbs are less than 6v?

The switch mode power supply generates different voltages to run the calculator, somewhere around +6V, +8V and -12V.

Quote:In my case regarding the drop when the card has triggered the mtr pin 17,
It drops to 4-5 MV so, not zero but is functioning correctly? Should I be good in that area?

The voltage won't be exactly zero, but close.

Quote:My power supply is designed for Quartz watch current and voltage measurements. There are several current draw and base lines when the watch is in operation

Maybe it is better to run the calculator from a charged battery, perhaps taped in position. This will supply the proper voltage and current for the calculator operation.

Quote:When I do the readings on the sense chip, I don’t see 6v anywhere only the Vbs supplied, and it will drop as required when a card goes in.

I was incorrect with the 6V logic HI signal. These are the voltages measured on the sense board connector just after switch on.

VSS 6.3
RA 3.6 - varies reading a card
RB 3.6 - varies reading a card
WE 0.13 - LO = Read, HI = Write
(Unused pin) 1.27
WB 3.6 - varies writing a card
WA 3.6 - varies writing a card
BATT 3.6
MOTOR 3.6 - HI = Motor OFF, LO = Motor ON
GND

So
3.6V will be HI logic
0.13 will be LO logic

Quote:Are there any desoldering points to isolate the chip that allow more trouble shooting for the 2.5 volts on pin 1? Perhaps the four red and black on the pcb, but leave the head wires untouched.

You could disconnect the motor red wire and see if it changes when a card is in.

Quote:To swap out the entire board of course all these would be desoldered. I was trying to reason a way to remove a fault by separating the circuit, to look for restored normal conditions. Like a short, that may exist PAST the sense chip, or a ground that isn’t supposed to be there.

Apart from disconnecting the motor lead, the listed voltages should be there for a given card operation. If they are then I would suspect the sense chip, given that you said the motor is working. If there is a discrepancy then it might be an open circuit between the CPU board and the sense chip, most likely at the sense board connector.

Quote:(I am a retired telephone company repairman, HA).

Funnily enough I worked as an install technician for the phone company here back in the 70's and 80's. It was a good job back then :-)

cheers

Tony