HP-65 more on the card reader

[albertofenini]

Here we go with some results !!
Of the four units we were able to fix two of them.
Here is what we found.

S/N 1503S09967
This unit had a broken trace from pin 14 of the Amplifier, that's the motor pin.
I did the repair myself years ago, and while doing this some soldering material had short circuited
with the adjacent trace.
We found out this with the oscilloscope.
RA and RB where good, WA was good while WB was always at +4 volts, since it was in short circuit
with the motor trace.
Once cleaned the short it worked straight away.
Amplifier on this unit is : 1826-0158

S/N 1333A06154
This unit had the HDS switch always closed to ground.
In this case we simply used the multimeter.
The brass switch was too lifted up, we did a small adjustment with the screw and it started to work.
Amplifier on this unit is : 1826-0158

Then the failures ....

S/N 1511A01736
This unit had a pinch roller done with silicone tubing, we replaced this with two orings
It had a 1826-0322 controller
The HDS WPS switchs sequence is good, i.e it knows when a card is protected or not
However, RA & RB are good, it read all the cards at the first try
We have a good WA and a bad WB signal (see attached photo)
We tried then the following :
replaced the Amplifier with 1826-0158 : same result
replaced both 22K capacitors : same result
replaced the magnetic head : same result
replaced the resistor : same result
swapped the logic board with another one : same result ...
What can we test now ???

RA & RB 1511A01736 :    

WA & WB 1511A01736:    

S/N 1333A20538
This unit had the worm gear rebuilt
The HDS WPS switchs sequence is good, i.e it knows when a card is protected or not
It reads the cards 80% of the times
It never writes
However :
RA & RB are good
WA and WB are good
What could it possible be ?

RA & RB 1333A20538 :    

WA & WB 1333A20538 :    

For all of them we have tuned the eccentric cam
For all of them we cleaned the head

Any suggestion will be more than welcome !!!