HP 97 restoration



#2

I have completed restoration of a HP 97 including that infamous idler gear and draw rolls for the paper and card reader drives and built a new battery pack. Everything in great except ...

The printed numbers are 'weak' at their bottom extremities. This suggests that there is insufficient backup toward the bottom. There doesn't appear to be any vertical adjustment of the print head. The pressure bar is not symmetrical. One edge is "v" shaped; the other is rounded. I don't know which position should be up or down but I have tried both with no apparent effect on the 'weak' bottom extremities. Can you offer any suggestions?

Bob Keller


#3

The V points downward.

The paper tear off bar must be in place for it to print properly, without it, the paper path does strange things and can cause light printing at the top or bottom of the line.

Have you checked the resistance of each print head resistor? Could be a bad head or driver transistors. The overall print intensity is set by R8 which can be anything from 34 to 196k.

All the details you'd ever want are in the 97 service manual on the MoHPC disk set. If you don't own one, it's time...


#4

The "v" is correctly down (thank you). The tear-off was is in place (thank you). The pixcels at the bottom appear to be there but don't print with enough intensity. Don't have the disks you refer to. Can you describe where these resistors are located and the resistance?


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