HP-65 goes on hold after reading a card

[albertofenini]

Hi Tony, Hi Everyone
we did a couple of tests, using the Biorithm Program which is 90 steps long

It reads ok from a card but if we examine the listing, after few steps a - minus appears at the right of the instruction code.
Usually this would mean that the end of the 100 steps memory has been reached, obviously this is not true.

The minus appears in multiple positions like at the 12th step, then at the 15th step, then in more positions but not in all the steps after the first appearance.

The unit goes on hold even just pressing RTN in the RUN mode after all the steps have been examined

We tried reading from different cards with the same result and if these cards
are used with a working unit everything runs ok.

If the program is inserted with the keyboard, everything goes well until about the step 70th,
after which more steps can still be keyed in but all will have the minus at the right of the instruction code.

Looks like not all the memory is working and can be used

Is there any possible fix ?
Is the problem in the Hybrid or somewhere else ?

Thanks for any possible hint !
Take care !

(11-18-2020 09:34 AM)albertofenini Wrote:  Hi Tony,

it's a behavior that few other HP-65s have shown in the past as well
Normally we have fixed this by swapping and mixing parts until they were working
Like it was a matter of finding a good match between the three main components,
the keyboard/display, the card reader and the logic

Certainly the keyboard/led plays a role in here, and we need to find out what it is
On the other side, on the keyboard/led there are only two active components, anode and cathode driver,
the two inductances for the led and the LC components ... not much to test ...

We where thinking to buy one of those portable microscope to look for bad traces, will see

There are not ICs getting warm and we are powering the units both via a rebuilt battery pack or via an external battery pack with a switch,
however the behavior seems not related to the kind of power source

We'll do more checks later today and we will let you knew
Thanks for the huge support !