HP-65 - card reader with WB wave noisy - FIXED and RESTORED

[albertofenini]

Dear All
we tried in the past to repair one of our HP-65 with partial success
The unit is working, can read cards but cannot writes them and we discovered that WB wave is very noisy.
It was all described in this thread :
HP-65 more on the card reader
All the single components work if used in conjunction with other HP65 hardware but when put together in this unit we have this problem.
Since we received few days ago some parts including a keyboard PCB we wanted to try this one.
The keyboard is without Anode and Cathode driver which we have used to repair another HP65
However, we have connected the card reader assembly including the battery compartment,
we have connected the logic board and turned on.
Of course the display is off, but we can feed cards.
Using an ohmeter We have checked that PRGM switch works and so work the motor, HDS, WPS switches
Using the scope we have seen normal waves on both RA and RB channels
But WA and WB when the unit is set to PRGM/W and we feed a blank card are FLAT
Does anyone know if Anode and Cathode driver have any influence on recording a card ?
More generally, has anyone ever fixed a situation like this ?
As always thanks for help !!!!