(02-02-2020 01:59 AM)coitboy2000 Wrote: Hi all
After several weeks of trying to get me HP-65 to read cards, including reading may threads and trying many things, I have not succeeded so decide now would be a good time to post something here.
My HP-65 works fine apart from the card reader. When I first got it a few months back I replaced the gummy wheel and the reader was working generally ok. Not 100% but it would read and write. It then stopped pulling the cards through for some reason.
I have tried/observed the following. Forgive my basic electronics understanding.
- several diameter silicon tubes but decided to stick with the tubing I know works in my HP-41 card readers.
- checked the capacitors(2x22uf) and (1x3.3uf) across the motor.
- soldered new motor wires and checked ground etc
- If I power the calculator from my bench top power supply (4.5v) the calculator draws about 120-130ma, if I insert a card I can see the motor shaft shift a small amount and the current draw increases to 165-170ma. It won’t pull the card though. If I measure the current at the motor it is about 15ma. I don’t see any real voltage across the motor red and white wires when the card appears to be sensed and the amp draw increases ? Odd ?
- if I power the card motor directly it pulls the card fine. With 1.5v it draws about 170ma from memory and with 3v it draws about 210-220ma when it pulls the card through.
Not sure what else to try. The fact that it was working makes me feel like a component has failed?
Any comments appreciated
Richard
Hi Richard
Here are some measurements...
My battery might be a little flat so your motor voltage may be a bit higher.
Voltage at card motor...
Idle close to 0V
Card reading 2.5V
Calculator current from battery...
0.00 displayed - 138mA
card read - 415mA
Because you changed the gummy wheel and therefore the drive diameter, the pressure from the new wheel to the card might have changed. You might have to adjust the cam which is the shaft for the helical gear.
cheers
Tony
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