HP-65 card reader problems

[coitboy2000]

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

[teenix]

(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

[coitboy2000]

Thanks Tony

I have rotated the cam in small increments over a full 360 deg. It does alter the current draw when I apply a voltage across the motor directly as expected. The main issue I think is that I cannot see any real voltage at the motor terminals when Insert a card ? The drive shaft does move axially but won't pull the card and I only measure some 50mv across the motor terminals ?

Richard

[teenix]

The motor voltage should appear on pins 1 and 3 of the sense chip. (3 being GND).

It is possible that the wiring to the sense board and charge pin terminals has been damaged where the insulation ends. Sometimes excessive movement can break most of the wires in the cables at this point and restrict current flow.

Check the connections to the sense resistor (4K64) near the top of the chip.

With the motor free running can it still run with a bit of friction applied, ie still produces torque?

Check that pin #11 on the sense chip goes to almost 0 volts when a card is inserted.

If all voltages and motor seem ok, then maybe the sense chip has failed. Do any parts feel warm to the touch?

cheers

Tony

[coitboy2000]

Thanks Tony

I will check everything you mention and let you know.

Cheers

Richard

[teenix]

(02-02-2020 09:44 AM)teenix Wrote:  Check that pin #11 on the sense chip goes to almost 0 volts when a card is inserted.

Apologies, that should have been pin #17.

Pin #18 should have constant 6V too.

If you don't have one, there is a circuit here...

http://www.hpcc.org/cdroms/schematics5.0...c/hp65.pdf

cheers

Tony

[coitboy2000]

Thanks Tony

I notice the red cap on the motor is damaged so hopefully that does not affect performance. Are HP-41 card reader motors a suitable replacement?

Richard

[teenix]

(02-04-2020 11:25 AM)coitboy2000 Wrote:  Thanks Tony

I notice the red cap on the motor is damaged so hopefully that does not affect performance. Are HP-41 card reader motors a suitable replacement?

Richard

I think it is just a dust cover. The sturdier inner plastic end plate has holes in it.

Sorry, I've never seen a HP-41 card reader so I don't know.

cheers

Tony

[coitboy2000]

I finally got an opportunity to check a few things.

The motor does have torque when a voltage is applied directly at the terminals.

The 4k64 resistor appears fine, i desoldered it and checked it. Continuity between it and yhe moyor is fine also.

When powered up and using pin 7 on the sense chip as ground i get the following voltages

Pin 1 0v
Pin 2 0v
Pin3 0v
Pin4 to pin6 1.4v
Pin8 to pin 10 1.4v
Pin11 0v
Pin 12 to pin14 3.85v
Pin15 3.6v
Pin16 3.9v
Pin17 3.7v
Pin18 3.9v
Pin19 6.2v
PIn20 3.9v

Not surr if this sheds anyblight on the matter. When insert a card i see a small increase in voltage to the motor of 60mv ?

Richard

[teenix]

The voltages seem to be ok, except that I measured the motor voltage (pin #1) on my scope to be be around 2.4V when it was running and 0 volts when off.

cheers

Tony

[coitboy2000]

Ok great

So what controls the voltage sent to the motor when a card is sensed ? That appears to be the issue.

Cheers

[teenix]

(02-16-2020 08:22 AM)coitboy2000 Wrote:  Ok great

So what controls the voltage sent to the motor when a card is sensed ? That appears to be the issue.

Cheers

When the card is detected in the slot by the CRC on the CPU board, it then sends a Logic LO signal to pin #17 of the sense chip which then outputs the motor drive voltage from pin #1. Some of this voltage is fed back to pin#2 through the 4K64 resistor to regulate the motor speed.

cheers

Tony

[coitboy2000]

Thanks Tony. Maybe its time to buy my first oscilloscope

[teenix]

(02-16-2020 10:21 AM)coitboy2000 Wrote:  Thanks Tony. Maybe its time to buy my first oscilloscope

You'll never regret it

A voltmeter will work for these measurements as they stay in that state while the card is in the slot, or at least until it times out if there is an error.

The Logic LO signal from the HDS to the CRC starts the process. This is on the CPU board connector pin #9. Pin #1 is marked on the board on the RHS looking down at it with the row of pins on the bottom.

cheers

Tony

[AndiGer]

Reading the thread I am thinking as it is not mentioned:
Did you check the motor switch closing when inserting a card? Carefully cleaned the contact?
It seems not so convenient to measure as on the 97 card reader with it's test points but should be possible ...
Andi

[teenix]

(02-16-2020 11:09 AM)AndiGer Wrote:  Reading the thread I am thinking as it is not mentioned:
Did you check the motor switch closing when inserting a card? Carefully cleaned the contact?
It seems not so convenient to measure as on the 97 card reader with it's test points but should be possible ...
Andi

Very good point. I mentioned this in previous post, but wasn't pursuing it earlier because of the mentioned symptom which I took to indicate that the motor was trying to move.

> The drive shaft does move axially but won't pull the card and I only measure
> some 50mv across the motor terminals

To be safe, remove the battery and CPU board, and with an ohm meter just measure from the keyboard pins, the pin I mentioned to GND. It should short when the card is inserted.

And my apologies, the CPU board pin #9 name is MTRS not HDS.
GND is pin #14.

cheers

Tony

[coitboy2000]

Good news. The reader is working perfectly. Bad news is all I did was dismantle it again for the 20th time, ran the motor for 15 sec with 3v directly, probed some of the logic board, and applied some upward pressure to the switch contact "fingers" incl the motor switch. Maybe it was thr switch contact after all.

Thanks everyone.

Richard

[AndiGer]

Thank you, Richard, for your feedback. Always good to know the advices here helped to repair another of our beloved calculators.
Andi

[teenix]

Good to see the problem turn out to be something simple in the end.

It doesn't take much for the switches to stop working, warped circuit board, bent contacts etc. Even though they might contact, the write protect also fails with those switches out of adjustment.

cheers

Tony