HP-67 - 1612S04538 - motor slow and wrong resistor value

[albertofenini]

Hi everyone, this was weird ...
It had the card reader motor running very slow, when connected and also when taken out it was barely running.
We used then a spare motor, but again when we connected it to the HP67 it was too slow to pull a card.
This HP67 is using an HP65 style card reader, we removed the resistor on top of the card reader and replaced it with a trimmer,
after some tests (this is when we used a different HP67 standard pac) we got it working in reading and writing.
We will need now to measure the trimmer value and replace it with a resistor.
BTW Has anyone ever opened a card reader motor and cleaned the inside ?
Pictures here : HP-67 1612S04538
As always, any advice is greatly appreciated,
Thanks for help !!!

[teenix]

(02-02-2020 10:13 PM)albertofenini Wrote:  BTW Has anyone ever opened a card reader motor and cleaned the inside ?

If the terminals are straight and clean the red cap should come off but is fragile.

However, I don't think the motor is designed to be serviceable. There is another clear plastic cover on the motor end that I am not sure can be removed without breaking it.

There are no carbon brushes in the motor. Instead there is a 5 segment commutator where the 2 power connectors rub against with small "fingers". If they are worn, I don't think they can be replaced. The motor coil connections may be broken but again I don't think they can be repaired easily.

Maxon made the motors originally by the look of it, but I haven't seen replacements. I have looked for 10,000rpm 3V motors with 1mm shaft and there are some around but no success so far with mechanical size and mounting screws.

Edit: It looks like Escap made motors as well. I think they are now called Portescap and they look to have promising models available.

cheers

Tony

[albertofenini]

Well, we worked a little on this unit but still is very unstable, let’s see if someone has an idea.
We replaced the trimmer, which measured 4.0 kohm, with the original resistor that measured 4.4 kohm and it worked fine.
That means it was able to read an entire standard pac although not the one we usually use for testing.
However, when we closed the unit with the back cover is started to act crazy.
Motor was going really slow and not pulling cards.
Removing the back cover put it back in working order.
We played a little with the screws, tightening or loosening the screws that keeps the back cover, including the two below the label, the we usually do not re-use.
We didn’t came to a conclusion though.
It is less stable than before but it started to read some of the cards of the previous standard pack.
However if the back cover is attached with the screws it “screws” the unit.
Only way to have it partially working is with a gummy and no screws.
We think is a problem of torsion, however the unit is in very good shape.
Of course we tried to tune the eccentric cam but with little to none results.
Any idea to share ??
Thanks for help !!!

[teenix]

(02-09-2020 09:16 PM)albertofenini Wrote:  Well, we worked a little on this unit but still is very unstable, let’s see if someone has an idea.
We replaced the trimmer, which measured 4.0 kohm, with the original resistor that measured 4.4 kohm and it worked fine.
That means it was able to read an entire standard pac although not the one we usually use for testing.
However, when we closed the unit with the back cover is started to act crazy.
Motor was going really slow and not pulling cards.
Removing the back cover put it back in working order.
We played a little with the screws, tightening or loosening the screws that keeps the back cover, including the two below the label, the we usually do not re-use.
We didn’t came to a conclusion though.
It is less stable than before but it started to read some of the cards of the previous standard pack.
However if the back cover is attached with the screws it “screws” the unit.
Only way to have it partially working is with a gummy and no screws.
We think is a problem of torsion, however the unit is in very good shape.
Of course we tried to tune the eccentric cam but with little to none results.
Any idea to share ??
Thanks for help !!!

Not sure what "gummy" means.

Hard to say, but have you checked that the keyboard is sitting properly in the front case. Sometimes it can go in without being properly seated. When screwed down, it can warp which will also warp the plastic card reader moulding. Maybe fitting the rear cover warps it a bit more just enough to cause the problem.

If this is the problem then the card reader won't be aligned properly to the card slots in the top case.

Have you checked the wiring from battery charger terminals to the card reader. If one has a bit of corrosion, it might go higher resistance when the back cover is fitted.

Is the eccentric cam adjustment ok?

cheers

Tony

[albertofenini]

Sorry, Tony I meant rubber band ...
I meant : when the unit is assembled with a rubber band and is out of the green front and back shells it works quite reliably.
This is a unit where all the plastic elements have been stripped and re-glued but it looks like everything is aligned.
We hope to have time over the next few days to do more tests, but the basics have been all checked.
No corrosion, no loose cables, no cold joints ...
Based on what happened wih an HP65 we are working on, it may be as well that the sense amplifier that is acting weird ...
You mentioned you wanted to make a replacement for the sense amplifier, how complex would it be ?
Take care !

[teenix]

(02-13-2020 12:54 PM)albertofenini Wrote:  Sorry, Tony I meant rubber band ...
I meant : when the unit is assembled with a rubber band and is out of the green front and back shells it works quite reliably.
This is a unit where all the plastic elements have been stripped and re-glued but it looks like everything is aligned.
We hope to have time over the next few days to do more tests, but the basics have been all checked.
No corrosion, no loose cables, no cold joints ...
Based on what happened wih an HP65 we are working on, it may be as well that the sense amplifier that is acting weird ...
You mentioned you wanted to make a replacement for the sense amplifier, how complex would it be ?
Take care !

It does sound like something is being twisted when assembled into the case. If the boards are placed into the front case they should not rock back and forth but should sit flat against the mounts built into the case. If they rock a bit then they will be bent out of true when screwed down.

(Tongue in cheek) I'm pretty sure about what needs to be done for a sense chip, but it would take time to come up with something useable.

cheers

Tony