collusions

Ecer come across a twisted pair _PCB track_? The HP9810 and HP9820 keyboard encoders need to feed a low level alanloge signal (the output of the keyboard sense loop) from the eddge commector to the keyboard itself to an analogue comparator cirucit at the other end of the encoder PCB. Fortunately the comaprator has differnetial inputs, the source of this signal is fully floating. I don't know if it depends on the version of the PCB, but the encoder in my HP9810 (and indeed in the other HP9810's I've worked on) uses a bit of twistwed pair wire for this. The HP9820 encoder has a pair of PCB tracks, They zig-zag over each other and go through the board (with vias), thus forming a twisted pair of conductors. It looks very odd... -tony