HP-80 with bugs ... ?

[ThomasF]

(02-12-2024 10:21 PM)teenix Wrote:  It sounds like it is not resetting properly if it works properly after a keypress.
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The reset circuit is based on a couple of transistors, resistors and a capacitor, shown in the image.
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If it fails completely, Harald from the Forum may still have replacement CPU boards for the Classics.

Hi Tony!

Thanks for your insights! Even if I'm missing the image ...

Yes, I actually just bought a board from Harald in the case the old board should fail completely, but I still hope to be able to fix it - that is at least my goal now that I have a backup plan!

And you are right, after power on, the stack is full of NaN's and most operations (like RDN or X<>Y) results in a blinking "0." - guess that is the normal way of showing a NaN when detected by the HP80.
With a NaN in the display, I can also recognize the digits from the NaN when normalizing the number (ie after SHIFT 9 to show all decimals).

So, hopefully it is only something dodgy with the reset circuit, and I will try to find some description of - maybe this is part of you excellent Classic Notes?

Cheers,
Thomas