HP-65 1333A04841 restoration it doesn't work anymore ...

[albertofenini]

Hi everyone, I’m restoring this unit but I definitely need some advice …
The unit was not in terrible conditions, but it had some oxidation on the card reader, on the keyboard pcb and on the cpu board
Gummy wheel to be done, but that was no surprise

After an initial cleaning it was working, although had this strange behavior: it never turned on at first try if it has been turned off since a while
You had to turn it off and then on again and it was working, after that you could turn it on and off with no problems
But if it was left off for a while, again, it needed a double try.
Also some times it was showing erratic behavior like in the video where after turning on it was showing a kind of a countdown
But at this stage it never showed erratic digits or partially lit segments

I cleaned the card reader pcb and the keyboard, and I did the gummy wheel with two glued o-ring
but at that time I didn’t want to bother the cpu board

The unit was reading and writing with no problems, I almost copied an entire standard pac

But, as you can hear in the videos, the noise of the card reader was not regular, it was like something was not centered,
As the noise was almost like a wave … nevertheless it was reading a writing without failures
I thought that after all gluing the o'ring could have caused some eccentricity

However, I didn’t like it, and this evening I tried to change the gummy wheel, at first with a small section of a silicone tubing
and later with two not glued o-rings

After I did this the unit was not reading anymore, although the card reader was now working smoothly as it should have been since the beginning

Then I swapped then this CPU board with a working one and I discovered that this configuration was reading with no
problems at all (though I didn’t test writing) while this CPU in another working chassis was still not reading

At this point I treated this CPU with water and vinegar and rinsed with isopropyl and let it dry well as I thought
that may be the oxidation on the CPU board I had seen was causing this problem

Sadly after that I haven't been able to get it working again, it only shows random digits totally meaningless as it can been seen in the last pictures
and it now needs several tries to turn on

What can I try or what can I check ?

Is reworking the board an option ?

I Have a set of spare ROMs, is this issue more a ROM or a Hybrid one ?

Thanks in advance for any help and take care !!

Pictures and videos can be seen here : HP-65 1333A04841