HP-97 troubleshooting

[teenix]

Well done, good news.

That makes sense now. Wiring the switch incorrectly would mess things up.

The switch has two functions.

When pressed it pulls the CRC F1 flag line low which tells the microcode you want to start doing paper advances until the button is released.

When not pressed, that ground signal goes to the out of paper switch which is normally open circuit when there is paper in the printer. When the paper is removed, the out of paper switch shorts and places this ground onto the FWD drive signal from the PIK chip, effectively stopping the motor until it reverses.

It makes sense to wire it this way as the out of paper switch is prevented from stopping the motor when the paper advance switch is pressed without paper in.

Not sure why the excess current as you didn't mention the motor was running. Depending on the way the switch wring was the PIK and CRC pins could have been shorted, or shorted to ground which may have cause a problem.

Anyway, all seems good.


cheers

Tony