HP35 problem with a calculator, maybe due to a faulty charger

[aurelio]

(03-21-2021 06:52 PM)teenix Wrote:  

(03-21-2021 04:43 PM)aurelio Wrote:  Well, if the voltage on test point is the one expected it means maybe that the PSU works properly, so what would be the next step in the troubleshooting?
What does it mean that if I use any of the numeric keyes, the calculator turns off, while clicking on the functions the display shows numbers that vary, from time to time, with different criteria?

I would try swapping a known good CPU. If you feel this is too risky, then Harald may still have replacement Classic CPU boards which you can try instead.

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It may be a faulty ROM.

When the keys are scanned, a key code is generated and this value is used as an address offset in ROM so that the processor can execute the code for that key press. Very efficient.

If the keycode is invalid, the Program Counter could be set to an incorrect ROM location causing the code to run in error.

If one or more ROMs have failed then code execution will fail also.

When a key is pressed, the display is turned off before processing begins. It is possible the code is still running but in a dodgy loop that makes the calculator look dead.

cheers

Tony

Thank-you Tony and thank- you Harald and congratulations for the HP Classic upgrade kit - Multi Emulator project .......I missed it when it was published, a few years ago
I'll follow your advices and meanwhile I'm "playing" with the faulty board with the presumption of understanding something more.
Yes maybe when i press a digit key "the display is turned off [....] it is possible the code is still running but in a dodgy loop that makes the calculator look dead.", I checked the test points and found alll the values of the calculator "on" and this maybe is a confirm that there's not been a power reset...