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

[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 !!!