HP97 The journey begins

[teenix]

Hi all,

I just found a potential problem with the 97, but I suspect there is only a very small chance it will actually happen.

There is a possibility that the print head is not in the home position when the calculator is switched on. Reasons for this could be, flat battery, switching off before printing finishes, etc.

If this is the case, then it will try to automatically home itself at switch on so it is ready for printing.

This is fine, but if the print head doesn't get detected as being home, the motor keeps on running continuously. The calculator still runs as normal, although you cannot print anything.

The problem is that if the print head can move, it will butt up against the printer casing and stall the motor. This may result in sheared teeth off the resin printer cog, or as I cannot see any current limiting circuitry, may burn out the motor or driver transistors.

This situation can occur (for example) if the home switch circuit does not work due to a fault or if due to maintenance, a white wire was left disconnected.

If a drive cog was broken then no risk of damage as the print head cannot move.

I haven't heard of this situation arising but you never know.

cheers

Tony